ADU & Construction Glossary

A

ADU (Accessory Dwelling Unit)

A secondary housing unit on a single-family residential lot, also known as in-law units, granny flats, or backyard cottages. ADUs provide independent living facilities including a kitchen, bathroom, and sleeping area.

Attached ADU

An ADU that shares at least one wall with the primary dwelling. Often created through additions or converting existing attached spaces like garages.

Accessory Structure

A building that is subordinate to and located on the same lot as the main building, such as a detached garage, shed, or workshop.

Amperage (Amps)

A unit of electrical current measuring the flow of electrons through a conductor. Residential panels typically range from 100-400 amps.

Architect

A licensed professional who designs buildings and structures, prepares construction documents, and may oversee construction. In California, architects must be licensed by the California Architects Board.

Architectural Drawings

Technical drawings that illustrate building design, including floor plans, elevations, sections, and details used for construction and permitting.

As-Built Drawings

Drawings that document the actual constructed conditions of a building, reflecting any changes made during construction from the original plans.

Attic

The space between the ceiling of the top floor and the roof. May be unfinished or converted into living space depending on height and access requirements.

Awning

A roof-like cover extending over a window, door, or patio to provide shade and weather protection. Can be fixed or retractable.

Air Barrier

A material or assembly that controls air leakage into and out of the building envelope. Critical for energy efficiency and moisture control in wall and roof assemblies.

Air Handler

The indoor component of an HVAC system that circulates conditioned air through ductwork. Contains the blower, filter, and often the evaporator coil.

Anchor Bolt

A bolt embedded in concrete foundations to secure the sill plate and connect the wood framing to the foundation. Required by code at specific intervals.

Appraisal

A professional assessment of property value, often required for financing. ADUs typically increase property values but appraisal methods vary by market.

AFCI (Arc Fault Circuit Interrupter)

An electrical safety device that detects dangerous arcing conditions and disconnects power to prevent fires. Required in bedrooms and other living areas by current codes.

Asphalt Shingles

The most common residential roofing material, made of fiberglass mat coated with asphalt and mineral granules. Available in various styles and fire ratings.

Assessor

A government official who determines property values for tax purposes. ADU construction may trigger reassessment of the new improvement value.

Accessible Design

Design features that accommodate people with disabilities, including wider doorways, grab bars, and barrier-free entries. May be required or voluntary in ADU construction.

ADA (Americans with Disabilities Act)

Federal law requiring accessible design in public accommodations. While residential ADUs are generally exempt, accessibility features can expand usability and market appeal.

B

Backflow Preventer

A plumbing device that prevents contaminated water from flowing backward into the clean water supply. Required at irrigation connections and certain plumbing fixtures.

Balloon Framing

A wood framing method where wall studs run continuously from foundation to roof, common in older construction. Now largely replaced by platform framing.

Baseboard

Molding installed at the base of walls where they meet the floor, covering the joint and protecting walls from damage.

Beam

A horizontal structural member that carries loads from the floor or roof to vertical supports like columns or walls. Common types include engineered lumber, steel, and glulam.

Bearing Wall (Load-Bearing Wall)

A wall that supports structural loads from above, such as floors, roofs, or other walls. Cannot be removed without providing alternative structural support.

Berm

An earthen mound or embankment used for landscaping, drainage control, or noise reduction. Sometimes used around structures for energy efficiency.

Blueprints

Traditional term for construction drawings, named for the blue-tinted reproduction process historically used. Now refers to any set of construction documents.

Building Code

Regulations governing the design, construction, and occupancy of buildings to ensure safety. California uses the California Building Standards Code (Title 24).

Building Department

The local government agency responsible for reviewing building plans, issuing permits, and conducting inspections to ensure code compliance.

Building Envelope

The physical barrier between the conditioned interior and unconditioned exterior, including walls, roof, windows, doors, and foundation. Critical for energy efficiency.

Building Permit

Official approval from the local building department authorizing construction work. Required before starting most construction projects.

By-Right

Development that is permitted under zoning without requiring discretionary approval such as variances or conditional use permits. California ADU laws establish by-right approval for qualifying ADUs.

Batt Insulation

Pre-cut sections of fiberglass or mineral wool insulation designed to fit between standard framing spacing. Available in various R-values and thicknesses.

Blocking

Short pieces of lumber installed between framing members to provide nailing surfaces, transfer loads, or prevent twisting. Required at specific locations by code.

Board Foot

A unit of lumber measurement equal to 144 cubic inches (12" x 12" x 1"). Used for pricing and estimating lumber quantities.

Bond (Construction)

A financial guarantee ensuring completion of work or payment of obligations. Types include performance bonds, payment bonds, and license bonds.

Building Area

The total covered footprint of a building measured at ground level. Used in lot coverage calculations and setback determinations.

Building Height

The vertical distance from grade to the highest point of the roof. California limits ADU height to 16 feet for detached units, with exceptions for specific configurations.

Built-Up Roof (BUR)

A flat roofing system consisting of alternating layers of bitumen and reinforcing fabrics, topped with gravel or a cap sheet. Durable but heavy.

Bump-Out

A small addition that extends a room beyond its original footprint, typically 2-4 feet. Often used to add space for bathrooms or kitchens in ADU conversions.

Butt Joint

A connection where two members meet end-to-end without overlapping. Requires additional fastening or support compared to overlapping joints.

C

CALGreen

California Green Building Standards Code (Part 11 of Title 24), the first state-mandated green building code in the US, establishing requirements for sustainable construction.

Cantilever

A projecting beam or floor structure supported only at one end, commonly used for bay windows, balconies, or extended floor sections.

Casement Window

A window hinged on the side that opens outward like a door, typically operated by a crank mechanism. Provides excellent ventilation and egress capability.

Caulking

Flexible sealant material applied to joints and gaps to prevent air and water infiltration. Essential for weatherproofing around windows, doors, and penetrations.

Ceiling Height

The vertical distance from the finished floor to the finished ceiling. Building codes typically require minimum 7-foot ceiling heights for habitable rooms.

Certificate of Occupancy (CO)

Document issued by the building department confirming that a building complies with codes and is safe for occupancy. Required before moving into a new ADU.

Change Order

A written amendment to the construction contract documenting changes to the scope, schedule, or cost of work. Should be signed by both owner and contractor.

Circuit Breaker

An automatic electrical safety device that interrupts current flow when it exceeds safe levels, protecting wiring and preventing fires.

Cladding

The exterior finish material applied to walls for weather protection and aesthetics. Includes siding, stucco, brick veneer, and panel systems.

Cleanout

An accessible opening in a drainage system allowing for pipe cleaning and inspection. Required at changes in direction and at regular intervals.

Code Compliance

Meeting all applicable building codes, zoning ordinances, and regulations. Essential for obtaining permits and certificates of occupancy.

Column

A vertical structural member that transfers loads from beams or floors to the foundation. Can be wood, steel, or concrete.

Conduit

Protective tubing for electrical wiring, providing physical protection and allowing wire replacement. Types include EMT, rigid metal, and PVC.

Construction Documents

The complete set of drawings and specifications used for construction and permitting, including architectural, structural, mechanical, electrical, and plumbing plans.

Construction Loan

Short-term financing for building projects, typically disbursed in draws as construction progresses. Often converts to permanent financing upon completion.

Contractor (General Contractor)

A licensed professional who manages construction projects, hires subcontractors, and ensures work is completed according to plans and specifications. In California, must hold a CSLB license.

Conventional Construction

Traditional site-built construction using standard framing methods, as opposed to modular or prefabricated construction.

Conversion ADU

An ADU created by converting existing space within the primary dwelling or an accessory structure, such as a garage, basement, or attic.

Crawl Space

A shallow, unfinished space between the first floor and ground, allowing access to utilities. Must be properly ventilated and vapor-protected.

CSLB (Contractors State License Board)

The California agency that licenses and regulates the construction industry, protecting consumers and ensuring contractor competence.

Concrete

A composite building material made from cement, aggregate, and water. Used for foundations, slabs, and structural elements with various strength specifications.

Concrete Block (CMU)

Concrete masonry units used for foundation walls, retaining walls, and structural elements. May be reinforced with rebar and grout for added strength.

Condensation

The process where water vapor becomes liquid on cold surfaces. Proper insulation and vapor barriers prevent condensation-related damage in wall and roof assemblies.

Copper Pipe

Metal tubing used for water supply lines, valued for durability and corrosion resistance. Types include M, L, and K with varying wall thicknesses.

Corner Bead

Metal or plastic trim installed on drywall corners to create straight, durable edges. Covered with joint compound for a finished appearance.

Cost Estimate

A detailed projection of construction costs based on plans and specifications. Typically includes materials, labor, permits, and contingency allowances.

Counter Flashing

Metal flashing embedded into walls or chimneys that overlaps base flashing to prevent water infiltration at roof intersections.

Cripple Stud

Short studs installed above and below wall openings to maintain framing layout and provide nailing surfaces for sheathing and finishes.

Crown Molding

Decorative trim installed at the junction of walls and ceilings. Adds architectural detail and can conceal imperfect corners.

Curb Appeal

The visual attractiveness of a property from the street. ADU design should complement the main house and maintain neighborhood character.

Curing

The process by which concrete hardens and gains strength. Proper curing requires moisture and temperature control for optimal results.

Cut Sheet

A manufacturer's product specification sheet detailing dimensions, performance, and installation requirements. Required for permit review of many products.

Curtain Wall

A non-structural exterior wall, typically glass and aluminum framing. Less common in residential but sometimes used in modern ADU designs.

Custom Home

A uniquely designed and built residence. Custom ADUs offer design flexibility but typically cost more than prefabricated or standard plans.

Cycle Time

The total duration from permit application to certificate of occupancy. Varies by jurisdiction and project complexity.

D

Deed Restriction

A limitation on property use recorded in the deed, which may restrict ADU construction. Some California laws override certain deed restrictions for ADUs.

Demolition Permit

Authorization required before demolishing or removing structures. May involve asbestos testing and utility disconnection requirements.

Design Review

A local process evaluating the aesthetic and architectural aspects of proposed construction. California limits subjective design review for ADUs.

Detached ADU

A stand-alone ADU that is separate from the primary dwelling, not sharing any walls. California allows detached ADUs up to 1,200 square feet.

Developer Fee

Charges imposed by local governments to fund infrastructure and public facilities. California limits impact fees for ADUs under 750 square feet.

Dormer

A roofed structure projecting from a sloped roof, containing a window and providing additional headroom and natural light in attic spaces.

Downspout

A vertical pipe carrying rainwater from gutters to ground level or drainage system. Proper sizing and placement prevents foundation damage.

DWV (Drain-Waste-Vent)

The plumbing system that removes wastewater and sewage while providing ventilation to prevent siphoning of trap seals and sewer gas entry.

Drywall (Gypsum Board)

Panel material made of gypsum plaster pressed between paper sheets, used for interior walls and ceilings. Standard thickness is 1/2" for walls and 5/8" for fire-rated assemblies.

Ductwork

The system of channels distributing heated or cooled air from HVAC equipment throughout a building. May be sheet metal, flexible, or fiberglass duct board.

Duplex

A building containing two separate dwelling units, either side-by-side or stacked. SB 9 allows lot splits that can create duplex opportunities on single-family lots.

Dead Load

The permanent, static weight of building materials and fixed equipment. Includes framing, roofing, flooring, and mechanical systems.

Deck

An outdoor platform typically made of wood or composite materials, attached to or adjacent to a building. Requires permits when elevated above grade.

Deflection

The bending of structural members under load. Building codes limit deflection to prevent cracking of finishes and ensure occupant comfort.

Dense Pack Insulation

Cellulose or fiberglass insulation installed at high density to reduce air movement and increase R-value. Common in retrofit wall insulation.

Detail Drawing

An enlarged drawing showing specific construction assemblies or connections at a larger scale than plan drawings for clarity.

Dimensional Lumber

Standard-sized lumber used for framing, such as 2x4, 2x6, and 2x12. Actual dimensions are smaller than nominal due to drying and planing.

Double-Hung Window

A window with two sashes that slide vertically, allowing ventilation from top or bottom. Both sashes may tilt inward for cleaning.

Drainage

The system for removing water from roofs, foundations, and sites. Proper drainage prevents flooding, foundation damage, and moisture problems.

Drip Edge

Metal flashing installed at roof edges to direct water away from the fascia and into gutters. Required by code on most roof installations.

Dry Rot

Wood decay caused by fungi, despite the name requiring moisture. Must be removed and replaced before new construction work.

Drywell

An underground structure that collects and disperses stormwater into the ground. May be required for drainage from ADU roofs and paving.

Dual Zone HVAC

A heating and cooling system with separate controls for different areas. Allows independent temperature control for ADU and main house.

Due Diligence

Thorough investigation before a major decision or purchase. Includes researching zoning, utilities, and feasibility before committing to an ADU project.

Dwelling Unit

A building or portion of a building designed for residential use, with independent living facilities. Each ADU is a separate dwelling unit.

Damper

A valve or plate controlling airflow in ductwork or chimneys. Manual or automatic dampers balance HVAC distribution and prevent backdrafting.

Daylight Harvesting

Using natural light to reduce artificial lighting needs. Strategic window placement and light shelves maximize daylighting in ADUs.

Decibel (dB)

A unit measuring sound intensity. Building codes specify maximum noise levels for HVAC equipment and sound transmission between units.

E

Easement

A right to use another's property for a specific purpose, such as utilities or access. ADUs typically cannot be built within easements.

Eave

The lower edge of a roof that projects beyond the wall, providing weather protection and architectural detail. Depth affects setback measurements in some jurisdictions.

Efficiency Unit

A small dwelling unit with combined living/sleeping space and kitchen facilities. California allows efficiency ADUs as small as 150 square feet.

Egress

A means of exiting a building, particularly in emergencies. Bedrooms require egress windows meeting minimum size and sill height requirements.

Electrical Panel

The main distribution point for electrical circuits in a building, containing circuit breakers or fuses. ADUs may require a subpanel fed from the main panel.

Electrical Permit

Authorization for electrical work, typically obtained separately from or as part of the building permit. Required for new circuits, panel upgrades, and significant modifications.

Elevation (Drawing)

An architectural drawing showing the vertical face of a building from the exterior. Elevations document exterior materials, window placement, and height relationships.

Energy Code (Title 24 Part 6)

California's building energy efficiency standards, among the most stringent in the nation. Affects insulation, windows, HVAC, lighting, and solar requirements.

Engineer

A licensed professional who designs structural, mechanical, electrical, or civil systems. Structural engineers are often required for ADU foundation and framing design.

Engineered Lumber

Manufactured wood products designed to be stronger and more stable than solid lumber, including LVL, I-joists, glulam beams, and LSL.

Excavation

The process of digging and removing earth for foundations, utilities, or grading. Requires proper shoring, drainage, and soil disposal.

Exhaust Fan

A ventilation device that removes indoor air to the outside, required in bathrooms and kitchens for moisture and odor control.

Exterior Finish

The visible outer surface materials of a building, including siding, stucco, paint, and trim. Must be compatible with local fire hazard severity zones.

ENERGY STAR

A US EPA program certifying energy-efficient products and buildings. ENERGY STAR appliances and windows help meet California's energy code requirements.

Encroachment

When a structure extends beyond property lines or into easements, setbacks, or public right-of-way. May require encroachment permits or removal.

Environmental Review

Analysis of a project's environmental impacts under CEQA (California Environmental Quality Act). Most ADUs are exempt from environmental review.

Equity (Home Equity)

The difference between a property's market value and outstanding mortgage balance. Often used to finance ADU construction through HELOCs or cash-out refinancing.

Erosion Control

Measures to prevent soil loss during and after construction, including silt fences, straw wattles, and vegetation. Required in many jurisdictions.

Escrow

A neutral third party that holds funds and documents during real estate transactions. Construction escrow accounts may be used for progress payments.

Evaporative Cooler (Swamp Cooler)

A cooling system that uses water evaporation to lower air temperature. Effective in dry climates and more energy-efficient than refrigerant-based air conditioning.

Expansion Joint

A gap between building elements allowing movement from thermal expansion, settling, or seismic activity without causing damage.

F

Fascia

The vertical board at the edge of a roof, covering rafter ends and providing a surface for gutter attachment. Material and size affect aesthetics and durability.

Feasibility Study

A preliminary analysis determining whether an ADU project is possible on a specific property, considering zoning, setbacks, lot coverage, and utility capacity.

Fee Simple

Complete ownership of real property, including the right to build, modify, or transfer. The most common form of property ownership for ADU projects.

Fire Blocking

Materials installed to prevent the spread of fire within concealed spaces such as wall cavities and soffits. Required at specified locations by building codes.

Fire Rating

The duration that building elements can resist fire, expressed in hours. Affects wall, floor, and roof assembly requirements, especially near property lines.

Fire Sprinklers

Automatic fire suppression system that releases water when activated by heat. California requires sprinklers in new ADUs when the primary dwelling has them.

Fireplace

A structure for containing fire, typically with a chimney or direct vent. Gas fireplaces are common in ADUs due to efficiency and air quality regulations.

Flashing

Sheet metal or membrane material installed at roof intersections, penetrations, and wall connections to prevent water intrusion. Critical for weatherproofing.

Floor Area Ratio (FAR)

The ratio of total building floor area to lot area, used to regulate building density. Many California cities exempt ADUs from FAR calculations.

Floor Joist

Horizontal framing member that supports floor loads, spanning between foundation walls, beams, or bearing walls. Sizing depends on span and load requirements.

Floor Plan

A drawing showing the horizontal arrangement of rooms, doors, windows, and fixtures as viewed from above. Essential for permit applications and construction.

Footing

The widened base of a foundation that distributes building loads to the soil. Size and reinforcement depend on soil conditions and structural loads.

Foundation

The structural system transferring building loads to the earth. Common types for ADUs include slab-on-grade, raised floor (crawl space), and pier/post foundations.

Framing

The structural skeleton of a building, typically wood or steel studs, joists, and rafters. Platform framing is standard for residential construction.

Furring

Thin strips of wood or metal attached to walls or ceilings to create an air space, level surfaces, or provide attachment for finish materials.

Fenestration

The arrangement and design of windows, doors, and other openings in a building. Critical for natural lighting, ventilation, and energy performance.

Fiber Cement Siding

Exterior cladding made from cement, sand, and cellulose fibers. Durable, fire-resistant, and available in various profiles mimicking wood or masonry.

Field Change

A modification to construction plans made during building. May require plan revision approval from the building department.

Final Inspection

The last building department inspection verifying all work is complete and compliant with approved plans and codes. Required before certificate of occupancy.

Finish Schedule

A document specifying materials and colors for surfaces including flooring, paint, tile, and fixtures in each room of a building.

Fire Hazard Severity Zone

State-designated areas of high wildfire risk requiring specific construction materials and vegetation management. Affects ADU requirements near wildland areas.

Fixed Window

A window that does not open, used primarily for light and views. Cannot serve as emergency egress but offers better energy efficiency and lower cost.

Flat Roof

A roof with minimal slope, typically less than 2:12 pitch. Requires specialized waterproof membrane roofing systems and proper drainage.

Floor Drain

A plumbing fixture in floors allowing water drainage. Required in laundry rooms, mechanical spaces, and shower areas without curbs.

Floor Leveler

Self-leveling compound used to create flat surfaces over uneven subfloors. Essential when installing tile or hardwood over concrete.

Flue

A pipe or channel carrying combustion products from appliances to the exterior. Proper sizing and installation are critical for safety.

Fluorescent Lighting

Lighting technology using gas-discharge tubes. Being replaced by LED for energy efficiency but still found in older buildings.

Flush Mount

A light fixture mounted directly against the ceiling with no gap. Appropriate for low ceiling heights common in some ADUs.

Foam Insulation

Spray-applied or board insulation made of polyurethane or polystyrene. Provides high R-value and air sealing in a single application.

Forced Air

A heating and cooling system using ductwork to distribute conditioned air. Common but requires space for ducts that may not fit in compact ADUs.

Formwork

Temporary molds that shape poured concrete until it cures. Forms may be wood, metal, or plastic; some are reusable.

Frame Wall

A wall constructed of dimensional lumber studs. Standard residential construction allowing for insulation within the wall cavity.

Freestanding (ADU)

A detached ADU separate from the primary dwelling. May have different height allowances and setback requirements than attached units.

French Door

A pair of glass-paned doors hinged on opposite sides. Popular for ADU entries and patio access, providing light and visual connection.

Frost Depth

The depth at which ground freezes in winter, affecting foundation depth requirements. California's mild climate allows shallower foundations.

Full Bath

A bathroom with toilet, sink, and bathtub or shower. Required for ADUs; the shower may substitute for a bathtub in accessible design.

Furnace

A heating appliance that warms air for distribution through ducts. Gas furnaces are being phased out in favor of heat pumps in new California construction.

G

Gable

The triangular portion of a wall between the edges of intersecting roof slopes. Gable roofs are common for ADUs due to simplicity and attic space.

Garage Conversion

Converting an existing garage into living space, often an ADU. California law prohibits requiring replacement parking when converting garages to ADUs.

General Contractor (GC)

A licensed contractor who oversees construction projects, coordinates subcontractors, and is responsible for completing work according to contract specifications.

Geotechnical Report

A soils engineering study analyzing ground conditions to determine appropriate foundation design. May be required on hillsides or in areas with poor soils.

GFCI (Ground Fault Circuit Interrupter)

An electrical safety device that shuts off power when it detects current leakage, preventing electrocution. Required in kitchens, bathrooms, and outdoor locations.

Glulam (Glued Laminated Timber)

Engineered wood made by bonding layers of lumber with adhesive, creating large, strong beams suitable for long spans and architectural exposure.

Grade

The ground level around a building, or the slope of land for drainage. Finish grade should slope away from foundations to prevent water infiltration.

Grading Permit

Authorization for significant earthwork including excavation, fill, and drainage modifications. Required for projects exceeding specified volume or depth thresholds.

Granny Flat

A colloquial term for an ADU, originally referring to small homes built for aging parents. Now used interchangeably with ADU, in-law unit, and guest house.

Green Building

Construction practices that reduce environmental impact through energy efficiency, sustainable materials, water conservation, and healthy indoor environments.

Greywater

Wastewater from showers, sinks, and laundry (not toilets) that can be recycled for landscape irrigation. California allows greywater systems with proper permits.

Gross Floor Area

The total floor area within the outside perimeter of a building, including all stories. Different from net or livable floor area which excludes walls and utility spaces.

Gutter

A channel at the roof edge that collects and directs rainwater to downspouts. Proper sizing and maintenance prevents water damage and foundation issues.

Gas Line

Piping that supplies natural gas or propane to appliances. Installation requires permits and inspection due to safety concerns.

Gazebo

A freestanding, open-sided outdoor structure. Unlike ADUs, gazebos are not habitable and have different permit requirements.

Girder

A large beam that supports other beams or floor joists, typically running perpendicular to joists. Common in raised floor foundations.

Glazing

Glass installed in windows and doors. Types include single, double, and triple pane with various coatings for energy efficiency and safety.

Gravel

Crushed stone used under foundations, around drainage systems, and as a landscaping material. Various sizes for different applications.

Ground Fault

An unintended electrical path between a current-carrying conductor and ground. GFCI devices detect ground faults and interrupt power to prevent shock.

Grounding

Connecting electrical systems to earth for safety, directing fault currents away from people and equipment. Required by electrical codes.

Guest House

A secondary dwelling traditionally without a full kitchen, used for guests. Many former guest houses now qualify as ADUs under California law.

Galvanized Steel

Steel coated with zinc for corrosion resistance. Used for framing, connectors, and exterior applications. Avoid contact with copper to prevent electrolysis.

Gasket

A sealing material between surfaces to prevent air or water leakage. Used around doors, windows, and mechanical connections.

Gauge

A measurement of thickness for metal and wire. Lower gauge numbers indicate thicker material. Critical for structural components and wiring.

Generator Panel

An electrical panel with transfer switch capability for connecting a backup generator. Useful for ADUs in areas prone to power outages.

Glass Block

Translucent masonry units used for walls allowing light while maintaining privacy. Common for bathroom windows and accent walls.

Glue Laminated Beam

An engineered beam created by laminating dimensional lumber with structural adhesive. Strong, stable, and can span long distances.

Gooseneck

A curved pipe fitting or fixture neck. Common in plumbing fixtures and electrical conduit transitions.

Grab Bar

A safety bar for support in bathrooms, required for accessible design. Blocking must be installed in walls during framing for secure mounting.

Granite

Natural stone used for countertops, flooring, and exterior applications. Durable but requires sealing and is heavier than engineered alternatives.

Greenboard

Moisture-resistant drywall formerly used in wet areas. Now largely replaced by cement board and fiberglass-faced products for tile substrates.

Greenhouse

A glass or plastic-enclosed structure for growing plants. Not habitable space; has different permit requirements than ADUs.

Ground Cover

Low-growing plants used for landscaping. May be required in landscape plans as part of ADU permit conditions.

Ground Rod

A copper-clad steel rod driven into the earth for electrical system grounding. Required depth and number depend on soil conditions.

Ground Wire

The bare or green-insulated conductor providing a safe path for fault currents. Required in all modern electrical installations.

Grout

Cement-based material filling joints between tiles. Available in sanded and unsanded varieties; sealing prevents staining and water penetration.

H

Habitable Space

Space used for living, sleeping, eating, or cooking. Has specific requirements for ceiling height, light, ventilation, and egress distinct from storage or utility areas.

Hardscape

Non-plant landscaping elements including patios, walkways, driveways, and retaining walls. Affects drainage, lot coverage calculations, and permeable surface requirements.

Header

A horizontal structural member spanning door and window openings, transferring loads around the opening to adjacent studs or posts.

Heat Pump

An HVAC system that moves heat between indoor and outdoor environments for both heating and cooling. Highly efficient and increasingly required in California new construction.

HELOC (Home Equity Line of Credit)

A revolving credit line secured by home equity, commonly used to finance ADU construction. Offers flexibility with variable interest rates.

Hip Roof

A roof where all sides slope downward to the walls, with no vertical ends. More stable in high winds than gable roofs but with less attic space.

HOA (Homeowners Association)

A private organization that governs a residential community. California law limits HOA ability to prohibit ADUs but allows reasonable architectural standards.

Hold Harmless Agreement

A contract provision protecting one party from liability for another's actions. Sometimes required by cities for non-conforming ADU conditions.

House Wrap

A synthetic material applied to exterior walls behind siding, providing weather resistance while allowing moisture vapor to escape. Common brands include Tyvek.

HVAC (Heating, Ventilation, Air Conditioning)

The building systems that provide thermal comfort and indoor air quality. ADUs may use mini-splits, through-wall units, or central systems.

Hanger (Joist Hanger)

Metal bracket that supports the end of a joist or beam where it connects to another member. Required for code-compliant framing connections.

Hazardous Materials

Substances that pose health or environmental risks, including asbestos, lead paint, and some chemicals. Testing may be required before renovation work.

Hearth

The floor area in front of and beneath a fireplace, made of noncombustible material. Size requirements vary by fireplace type and local codes.

HERS Rating

Home Energy Rating System index measuring building energy efficiency. California requires HERS testing and verification for new construction compliance.

Hillside Lot

Property on sloped terrain requiring special engineering for foundations, drainage, and structural support. May have additional permit requirements.

Hollow Core Door

A lightweight interior door with a hollow center. Not suitable for fire-rated or exterior applications; solid core doors required where fire rating is needed.

Horizontal Bracing

Structural elements resisting lateral forces in the horizontal plane, including floor diaphragms and roof diaphragms that transfer loads to vertical resisting elements.

Hurricane Clip (Tie)

Metal connector securing roof framing to wall framing, preventing uplift from wind forces. Required in many jurisdictions and by insurance.

Half Bath

A bathroom with only a toilet and sink, no shower or bathtub. Also called a powder room. May be adequate for studio or one-bedroom ADUs.

Handrail

A graspable rail along stairs or ramps for support. Building codes specify height, size, and return requirements for safety.

Hardwood Flooring

Solid or engineered wood flooring prized for durability and appearance. Engineered hardwood is often preferred for ADUs due to stability over concrete.

HRV (Heat Recovery Ventilator)

A ventilation device that transfers heat from exhaust air to incoming fresh air, improving energy efficiency while maintaining indoor air quality.

Heating Degree Day

A measure of how cold a location is, used for energy calculations. Higher values indicate greater heating needs.

Heel Height (Truss)

The vertical distance from the top plate to the top of a truss at the eave. Greater heel height allows more insulation at roof edges.

Heritage Tree

A protected tree due to age, size, or species. May limit ADU placement and require special permits or mitigation for removal.

Hidden Fastener

Mounting hardware that is not visible in the finished installation. Used for decking, siding, and trim for cleaner appearance.

HET (High Efficiency Toilet)

A toilet using 1.28 gallons per flush or less, compared to the 1.6 gallon federal standard. Required by CALGreen for new construction.

Historic District

A designated area with special protections for historic character. ADUs in historic districts may face additional design review requirements.

Holddown

Metal hardware anchoring shear walls to foundations, resisting uplift from lateral forces. Size and spacing specified by structural engineer.

Hood (Range Hood)

A ventilation device over cooking surfaces to remove smoke, heat, and odors. Must exhaust to the exterior per code.

Hose Bibb

An outdoor faucet for connecting garden hoses. Frost-proof models are recommended; location affects landscape irrigation access.

Hot Mop

A waterproofing method using hot asphalt applied to shower pans and built-up roofing. Traditional but still effective technique.

Housing Element

A required component of California city and county general plans addressing housing needs. ADU-friendly policies help meet housing element goals.

I

Impact Fees

Charges imposed on new development to fund public infrastructure. California exempts ADUs under 750 sq ft from impact fees and limits fees for larger ADUs.

In-Law Unit

A common term for an ADU, originally referring to housing for extended family members. Now used interchangeably with ADU, granny flat, and accessory apartment.

Inspection

Official examination of construction work by building department staff to verify code compliance. Required at specific stages including foundation, framing, and final.

Insulation

Material that reduces heat transfer through the building envelope. Types include fiberglass, cellulose, spray foam, and rigid board, with R-value indicating thermal resistance.

Interior ADU

An ADU created within the existing space of a primary dwelling, such as converting a basement, attic, or portion of the house.

I-Joist

Engineered wood framing member with top and bottom flanges connected by a vertical web, resembling the letter I. Used for floors and roofs.

Infiltration (Air)

Uncontrolled air leakage into a building through cracks and openings. Reduces energy efficiency and can cause moisture problems.

Inlet (Plumbing)

A point where water enters a fixture or system. Inlet valves control water flow to toilets, water heaters, and other fixtures.

Insurance (Construction)

Coverage protecting against construction risks including liability, property damage, and workers' compensation. Contractors must carry appropriate insurance.

Interior Partition

A non-load-bearing wall that divides interior spaces. Can be added, moved, or removed without structural modifications.

Irrigation System

A system for watering landscaping, including sprinklers, drip systems, and controllers. May require separate permits and backflow prevention.

Isometric Drawing

A three-dimensional representation showing plumbing or electrical systems without perspective distortion. Used to clarify complex assemblies.

Ice Dam

Ice buildup at roof edges preventing drainage, causing water backup. Prevention requires proper attic insulation and ventilation.

I-Joist

An engineered wood product with an I-shaped cross section, used for floor and roof framing. Lighter and often stronger than solid lumber joists.

In-Fill

Construction on vacant or underutilized lots in developed areas. ADUs represent a form of in-fill development within existing neighborhoods.

Infiltration

Uncontrolled air leakage through gaps in the building envelope. Reduces energy efficiency and comfort. Measured by blower door testing.

Inlet

An entry point for water, air, or other substances. Includes storm drain inlets, fresh air intakes, and water supply connections.

Inspection Card

A document posted on the job site recording required inspections and their results. Must be visible and accessible to inspectors.

Interior Designer

A professional who plans interior spaces for function and aesthetics. May help with ADU finish selections, furniture layout, and color schemes.

Interlock

A safety device preventing improper operation. Includes electrical interlocks for generator panels and mechanical interlocks for HVAC systems.

Island (Kitchen)

A freestanding counter unit in a kitchen. May include seating, storage, and appliances. Requires careful planning in compact ADU kitchens.

J

JADU (Junior ADU)

A small ADU of 500 sq ft or less created within the walls of an existing single-family home. Must have separate entrance and efficiency kitchen; bathroom may be shared.

Jamb

The vertical side pieces of a door or window frame. Door jambs include hardware locations for hinges, strike plates, and weatherstripping.

Joist

A horizontal structural member supporting floors or ceilings, spanning between beams or bearing walls. Spacing is typically 12", 16", or 24" on center.

Junction Box

An electrical enclosure where wires are connected and spliced. Must remain accessible and covered with appropriate rated covers.

Jack Rafter

A short rafter that runs from a hip or valley rafter to the ridge or wall plate, not spanning the full roof.

Jack Stud (Trimmer)

A shortened stud that supports the ends of headers over door and window openings. Works with king studs to transfer loads.

Joint Compound

Material used to fill seams between drywall panels and cover fastener holes. Applied in multiple coats and sanded for a smooth finish.

Joint Tape

Paper or fiberglass mesh tape embedded in joint compound to reinforce drywall seams and prevent cracking.

K

Kilowatt (kW)

A unit of electrical power equal to 1,000 watts. Solar panel systems are rated in kilowatts, and electrical service capacity is often expressed in kW.

Kitchen

A room or area for food preparation with cooking appliances, sink, and storage. Full ADUs require complete kitchens; JADUs may have efficiency kitchens without full-size ranges.

Knee Wall

A short wall, typically under 4 feet, often found in attic conversions where the roof slope meets the floor. Creates usable space under low ceilings.

Key (Lock)

ADU entrances require independent locking systems. Consider whether to share master key systems with the primary dwelling.

Kick Plate

A protective metal plate at the bottom of a door to prevent damage from foot traffic. Common on commercial doors and accessible entries.

King Stud

Full-length studs on either side of an opening that run from the bottom plate to the top plate, supporting header loads.

Knob and Tube Wiring

An obsolete electrical wiring method using ceramic insulators. Must be replaced during renovations and not covered with insulation.

L

Lateral Load

Horizontal forces acting on a structure, primarily from wind and earthquakes. Resisted by shear walls, diagonal bracing, or moment frames.

Lath

The base material for stucco or plaster, traditionally wood strips but now typically metal mesh (expanded metal lath) or self-furring wire.

LEED (Leadership in Energy and Environmental Design)

A green building certification program rating projects on sustainability criteria including energy, water, materials, and indoor environmental quality.

Lien

A legal claim against property as security for payment. Contractors and suppliers can file mechanics' liens for unpaid work or materials.

Lintel

A horizontal member spanning an opening in masonry construction, similar to a header in wood framing. May be steel, precast concrete, or reinforced masonry.

Load-Bearing

A structural element that supports weight from above, including walls, beams, and columns. Removal or modification requires structural engineering.

Lot Coverage

The percentage of a lot covered by buildings and impermeable surfaces. Zoning codes set maximum lot coverage, though ADUs often receive exemptions or allowances.

Lot Line

The legal boundary of a property parcel. Setbacks are measured from lot lines, and construction typically cannot cross them without easements.

Low-E Glass

Window glass with a microscopically thin metallic coating that reflects radiant heat, improving energy efficiency. Required by California energy code for most applications.

LVL (Laminated Veneer Lumber)

Engineered lumber made from thin wood veneers bonded together, used for headers, beams, and rim boards. Stronger and more stable than solid lumber.

Landscape Plan

A drawing showing proposed vegetation, hardscape, and irrigation. May be required for ADU projects in some jurisdictions, especially in drought-prone areas.

Lap Siding

Horizontal siding where each board overlaps the one below. Available in wood, fiber cement, and vinyl. Classic appearance suitable for many ADU styles.

Ledger Board

A horizontal framing member attached to an existing structure to support floor or deck joists. Must be properly flashed and fastened per code.

Legal Nonconforming

A use or structure that was lawful when established but no longer complies with current regulations. May be allowed to continue with restrictions on expansion.

Licensed Contractor

A construction professional holding a valid state license. California requires CSLB licensing for contractors on projects over $500.

Light Fixture

An electrical device for mounting and powering light sources. Selection affects energy efficiency, lighting quality, and code compliance.

Live Load

Variable weight from occupants, furniture, and movable objects. Building codes specify minimum live load requirements for structural design.

Loft

A raised platform or partial floor within a room, often used for sleeping in compact ADUs. Height and access requirements vary by code.

M

Main Panel

The primary electrical distribution panel in a building, receiving power from the utility and distributing it to branch circuits. May need upgrading for ADU electrical loads.

Manufactured Housing

Factory-built homes constructed to federal HUD standards, distinct from modular homes built to local codes. Not typically permitted as ADUs in most jurisdictions.

Mechanical Permit

Authorization for HVAC system installation and modification. May be separate from or included in the building permit depending on jurisdiction.

Meter

A device measuring utility consumption. ADUs may share meters with the primary dwelling or have separate meters, affecting billing and utility connections.

Mini-Split

A ductless HVAC system with an outdoor compressor and one or more indoor air handlers. Popular for ADUs due to efficiency, compact size, and easy installation.

Ministerial Approval

Permit approval based on objective standards without discretionary judgment. California requires ministerial ADU approval within 60 days for compliant applications.

Modular Construction

Building method where sections are manufactured off-site and assembled on the property. Must meet the same codes as site-built structures and is increasingly popular for ADUs.

Moisture Barrier

Material that prevents water vapor transmission, installed in crawl spaces, under slabs, and within wall assemblies to prevent condensation and moisture damage.

Mold

Fungal growth resulting from moisture problems, causing health issues and structural damage. Prevention requires proper ventilation, drainage, and moisture control.

Multifamily

A building containing multiple dwelling units, such as apartments, condos, or townhouses. California ADU laws also apply to multifamily properties with specific provisions.

Manhole

An access point in underground utility systems. May be required for sewer connections depending on depth and local requirements.

Mansard Roof

A roof with two slopes on each side, the lower slope being steeper. Creates usable attic space and distinctive architectural character.

Masonry

Construction using brick, stone, concrete block, or similar units. Used for foundations, walls, chimneys, and decorative elements.

MEP (Mechanical, Electrical, Plumbing)

The building systems that provide comfort, power, and water. MEP design is critical for ADU functionality and code compliance.

Meter Base

The mounting equipment for an electric meter. ADUs may require a separate meter base or connection through a subpanel.

Miter Joint

A joint formed by cutting two pieces at matching angles, typically 45 degrees, to form a corner. Common in trim and molding work.

Moment Frame

A structural system using rigid beam-column connections to resist lateral forces. Allows open floor plans without diagonal bracing.

Mortar

A mixture of cement, sand, and water used to bind masonry units. Different types are specified for various applications and exposures.

Mullion

A vertical or horizontal member dividing a window or door into sections. May be structural or purely decorative.

N

NEC (National Electrical Code)

The standard for safe electrical installation in the United States, adopted with modifications by most jurisdictions. Updated on a three-year cycle.

Natural Light

Daylight entering through windows and skylights. Building codes require minimum glazing area (typically 8% of floor area) for habitable rooms.

Noncombustible

Materials that will not ignite, burn, or release flammable vapors. Required for certain applications, especially near property lines or in fire-prone areas.

Nonconforming

A structure or use that was legal when built but doesn't meet current zoning requirements. Existing nonconforming setbacks may be allowed for ADU conversions.

Nail Gun (Pneumatic Nailer)

A power tool that drives nails using compressed air. Essential for efficient framing and finish work. Different types for different nail sizes.

Nail Plate

A metal plate installed over studs to protect wires and pipes from nail or screw penetration. Required by code where utilities run near the face of framing.

Natural Gas

A fossil fuel delivered by pipeline for heating, cooking, and hot water. New California construction increasingly requires all-electric design.

Net Zero

A building that produces as much energy as it consumes annually, typically through solar generation and high efficiency. A goal for sustainable ADU design.

New Construction

Building a structure from the ground up, as opposed to renovation or conversion. New construction ADUs must meet current code requirements.

Noise Ordinance

Local regulations limiting noise levels and construction hours. ADU construction must comply with restrictions on work hours and noise levels.

O

Occupancy

The classification of building use (residential, commercial, etc.) and the number of people permitted. Residential occupancy codes apply to ADUs.

On Center (OC)

Measurement from the center of one framing member to the center of the next. Standard stud spacing is 16" OC, though 24" OC is common in some applications.

Open Floor Plan

A layout with minimal walls between living areas, popular in ADUs to maximize perceived space. Requires careful attention to structural support and mechanical systems.

OSB (Oriented Strand Board)

Engineered wood panel made from compressed wood strands, used for sheathing and subflooring. Performance is similar to plywood at lower cost.

Outlet

A point in the electrical system where current is taken to supply equipment. Receptacle outlets must be installed per NEC spacing requirements.

Overhang

Roof extension beyond the exterior wall, providing shade and weather protection. Depth affects solar heat gain and rain protection at windows and doors.

Owner-Builder

A property owner who acts as their own general contractor. Requires signing a disclosure acknowledging responsibilities and may affect insurance and financing.

Occupant Load

The calculated number of people a space can accommodate, used for determining egress, plumbing fixtures, and ventilation requirements.

Offset

A horizontal change in direction of a plumbing drain line. Requires proper fittings and may need additional cleanouts for maintenance access.

One-Hour Rated

A wall or floor assembly that can resist fire for one hour. May be required for ADUs within certain distances of property lines.

Operable Window

A window that can be opened for ventilation. Building codes require operable windows in bedrooms for emergency egress and in living spaces for natural ventilation.

Overlay (Zoning)

Additional zoning regulations applied to specific areas such as historic districts, hillsides, or transit corridors. May affect ADU requirements.

P

Panelized Construction

A building method using pre-assembled wall, floor, and roof panels manufactured off-site. Faster than stick-built and more customizable than modular.

Parcel

A legally defined piece of real property. ADUs must be located on the same parcel as the primary dwelling unless the parcel is subdivided under SB 9.

Parking

Off-street vehicle storage. California prohibits parking requirements for ADUs near transit, in historic districts, or when converting existing structures.

Passive Solar

Design strategies that use building orientation, windows, and thermal mass to collect and store solar energy without mechanical systems.

Patio

An outdoor living area typically at ground level, made of concrete, pavers, or other paving materials. Generally does not require a building permit unless covered.

Pedestal Foundation

A foundation system using isolated concrete piers to support the structure, often used for additions and ADUs to minimize site disturbance.

Permit

Official authorization from government agencies to perform construction work. ADU projects typically require building, electrical, plumbing, and mechanical permits.

Permit-Ready Plans

Pre-designed ADU plans that meet common code requirements and can be submitted for permit with site-specific modifications. Reduces design time and costs.

Pier

A vertical foundation element that transfers loads deep into the soil, used when surface soils are inadequate. May be drilled concrete, driven piles, or helical piers.

Plan Check

Review of construction documents by the building department for code compliance. California limits ADU plan check time to 60 days.

Platform Framing

Standard wood framing method where each floor is built as a separate platform, with wall studs extending only one story. The most common residential framing system.

Plumbing Permit

Authorization for plumbing work including water supply, drainage, and fixtures. May be obtained separately or as part of the building permit.

Plywood

Engineered wood panel made from thin veneer layers bonded with alternating grain directions. Used for sheathing, subflooring, and structural applications.

Point of Connection

The location where a new utility service connects to existing infrastructure. ADU utility connections may tap existing house services or require new connections.

Post and Beam

A structural system using vertical posts and horizontal beams to create open floor plans without load-bearing walls. Popular for modern architectural designs.

Prefabricated (Prefab)

Building components manufactured off-site and assembled on location. Includes modular units, panelized systems, and pre-built components. Growing segment of ADU market.

Primary Dwelling

The main residential structure on a property, to which an ADU is accessory. California ADU laws require a primary dwelling to exist or be proposed concurrently.

Property Line

The legal boundary of a parcel. Setbacks are measured from property lines, and structures typically cannot encroach without easements or variances.

PV System (Photovoltaic)

Solar panels that convert sunlight to electricity. California requires solar on most new construction, including some ADUs, depending on size and energy use.

Parapet

A low wall extending above the roof line. Common on flat-roofed buildings, providing edge protection and concealing rooftop equipment.

Parge Coat

A thin cement plaster applied to masonry or concrete surfaces for smoothing, waterproofing, or decoration.

Partition Wall

A non-load-bearing wall dividing interior spaces. Can be easily modified or removed without affecting structural integrity.

Passive House

An energy-efficiency building standard emphasizing airtight construction, continuous insulation, and heat recovery ventilation. Achievable for high-performance ADUs.

Patio

An outdoor living area, typically paved, at ground level. May be included in ADU designs for outdoor access and additional living space.

Paver

Interlocking concrete, brick, or stone units for paving driveways, patios, and walkways. Permeable pavers can help with stormwater management.

Peck Test

Exploratory excavation to determine soil conditions before foundation design. May reveal underground obstacles or inform engineering decisions.

Pedestal

A support post for raised flooring or deck systems. Adjustable pedestals simplify leveling over uneven surfaces.

Pergola

An outdoor structure with open-beam roof, providing partial shade. Often included in ADU landscape design for outdoor living space.

Perlite

Volcanic glass expanded by heat, used as lightweight insulation fill or aggregate in concrete. Provides thermal and acoustic benefits.

Phase (Electrical)

The type of electrical power service. Residential is typically single-phase; some large properties have three-phase service.

Pier

A vertical support column, often of concrete, extending from footings to support floor framing. Common for raised floor foundations.

Pilot Hole

A small-diameter hole drilled before inserting a screw, preventing wood splitting. Essential for hardwoods and near board edges.

Pitch Pocket

A metal flashing container filled with sealant around roof penetrations. Common detail for pipes, conduits, and supports on flat roofs.

Plan Check

The review of construction drawings by the building department for code compliance before permit issuance. California limits ADU plan check times.

Plate Height

The distance from the floor to the top plate of a wall, determining rough ceiling height. Standard is 8 feet; higher plates create roomier spaces.

Plenum

An air-handling space in HVAC systems, such as the chamber in furnaces or the space above dropped ceilings used for air distribution.

Plug Load

The electrical power consumed by devices plugged into outlets. Energy modeling considers plug loads in addition to fixed equipment.

Pocket Door

A door that slides into a wall cavity rather than swinging open. Saves floor space in compact ADU layouts.

Q

Quarter Round

Molding with a quarter-circle profile, often used at the base of baseboards to cover gaps between the baseboard and floor.

Quality Control

Systematic processes ensuring construction meets plans and specifications. Includes inspections, testing, and documentation throughout the project.

Quoin

Decorative stone or brick blocks at building corners, providing visual accent. May be genuine masonry or simulated with stucco or foam.

R

R-Value

A measure of thermal resistance in insulation materials. Higher R-values indicate better insulating performance. California energy code specifies minimum R-values by climate zone.

Rafter

A sloped framing member extending from the ridge or hip to the wall plate, supporting roof sheathing and loads. Sized based on span, spacing, and load requirements.

Raised Floor

A floor elevated above grade on piers or a short foundation wall, creating a crawl space beneath. Provides utility access and flood protection.

Rear Setback

The required distance between a structure and the rear property line. California allows ADUs within 4 feet of rear property lines when meeting height limits.

Rebar (Reinforcing Steel)

Steel bars embedded in concrete to increase tensile strength. Size, spacing, and placement are specified by structural engineers based on loads and codes.

Receptacle

An electrical outlet for plug-in devices. NEC requires receptacles at specific intervals, near counters, and in bathrooms, garages, and outdoor locations.

Rental Income

Revenue from renting an ADU, which can help offset construction costs and mortgage payments. Lenders may consider projected rental income for ADU financing.

Retaining Wall

A structure that holds back soil at different elevations. Required on sloped sites and may need engineering and permits depending on height and location.

Ridge

The highest point of a roof where two slopes meet. Ridge height often determines overall building height for setback and zoning calculations.

Rim Joist

The perimeter joist at the edge of a floor system, enclosing the ends of floor joists. Important for insulation and air sealing at the floor-wall junction.

Riser

The vertical portion of a stair step. Building codes specify maximum riser height (typically 7 3/4") and require uniform risers in a flight of stairs.

Roof Pitch

The slope of a roof expressed as rise over run (e.g., 4:12 means 4 inches of rise per 12 inches of horizontal run). Affects drainage, attic space, and aesthetics.

Rough-In

Installation of mechanical, electrical, and plumbing systems within walls and floors before covering with finish materials. Requires inspection before closing up.

Radiant Heating

A heating system using panels or tubing in floors, walls, or ceilings to radiate heat. Provides comfortable, even heat distribution without ducts.

Rain Screen

A wall system with an air gap between siding and sheathing, allowing drainage and drying of moisture that penetrates the cladding.

Rake

The sloped edge of a gable roof, running from eave to ridge. Rake trim protects the exposed roof edge and provides architectural detail.

Range Hood

A ventilation device over a cooking surface that removes smoke, grease, and odors. Required in ADU kitchens and must vent to the exterior.

Return on Investment (ROI)

The financial gain relative to investment cost. ADUs typically provide strong ROI through rental income and property value increases.

Revision (Plan)

Changes to approved plans requiring review and approval by the building department. Major revisions may incur additional fees and review time.

Right of Way

Land reserved for public use such as streets, sidewalks, and utilities. Structures cannot typically be built in the public right of way.

Romex (NM Cable)

Non-metallic sheathed cable used for interior residential wiring. Contains insulated conductors and ground wire within a plastic jacket.

Roof Drain

A drain installed in a flat roof to remove water, connected to an internal drainage system or scupper. Requires regular maintenance.

S

SB 9 (California Senate Bill 9)

California law (2022) allowing lot splits and duplexes on single-family lots in urban areas, potentially enabling up to four units per parcel when combined with ADUs.

SB 13 (California Senate Bill 13)

2019 California law that reduced ADU development barriers, including eliminating owner-occupancy requirements and limiting impact fees for smaller ADUs.

Schematic Design

The initial design phase establishing overall project scope, size, and character through basic drawings and diagrams before detailed design development.

Scope of Work

A detailed description of work to be performed under a contract, including materials, methods, and outcomes. Essential for accurate bids and avoiding disputes.

Septic System

An on-site sewage treatment system using a tank and leach field. ADUs on septic properties may require system evaluation and potential upgrades.

Setback

The required distance between a structure and property lines. California limits ADU setbacks to 4 feet from side and rear property lines for compliant projects.

Sewer Lateral

The underground pipe connecting a building's drainage system to the public sewer main. ADUs may connect to existing laterals or require new connections.

Shear Wall

A wall designed to resist lateral forces from wind and earthquakes through rigid sheathing and proper fastening. Essential for structural stability.

Sheathing

Structural panels (plywood or OSB) attached to framing to provide rigidity and a surface for exterior finishes. Also provides lateral bracing for walls.

Shed Roof

A single-slope roof, simple to construct and popular for modern ADU designs. Allows for clerestory windows and easy drainage.

Short-Term Rental

Renting property for less than 30 days, typically through platforms like Airbnb. Many California cities restrict or prohibit short-term ADU rentals.

Siding

Exterior wall cladding providing weather protection and aesthetics. Types include wood, fiber cement, vinyl, and metal. Some require fire-resistant materials near property lines.

Sill Plate

The lowest horizontal member of a wall frame, anchored to the foundation. Must be pressure-treated or naturally decay-resistant when in contact with concrete.

Single-Family

A zoning classification for properties with one primary dwelling unit. California ADU laws primarily apply to single-family zoned properties.

Site Plan

A drawing showing the property boundaries, existing and proposed structures, setbacks, utilities, and other site features. Required for ADU permit applications.

Skylight

A window in the roof providing natural light and, in some designs, ventilation. Requires proper flashing and may contribute to required light and ventilation.

Slab-on-Grade

A concrete foundation poured directly on prepared ground, serving as both foundation and floor. Common for ADUs due to cost-effectiveness and accessibility.

Slope

The incline of land, expressed as ratio or percentage. Steep slopes affect ADU feasibility, foundation design, drainage, and access requirements.

Smoke Detector

A device that detects smoke and sounds an alarm. Required in each bedroom, outside sleeping areas, and on every level of an ADU. May need to be interconnected.

Soffit

The underside of an overhanging element such as a roof eave. Provides ventilation for attic spaces and protects rafter ends from weather.

Soils Report

A geotechnical study analyzing soil conditions to determine appropriate foundation design. May be required for hillside sites or areas with problematic soils.

Solar Ready

Design features facilitating future solar panel installation, including conduit pathways, electrical panel capacity, and unobstructed roof area.

Span

The horizontal distance between supports for a structural member. Span tables in building codes specify allowable spans based on member size, spacing, and loads.

Specifications

Written descriptions of materials, products, and workmanship standards supplementing construction drawings. Part of the complete construction documents.

Square Footage

The area of a space measured in square feet. ADU size limits vary by jurisdiction, with California setting a state minimum of 850-1,200 sq ft depending on bedroom count.

Stormwater

Rainwater runoff from roofs and paved surfaces. New impervious area may trigger stormwater management requirements including retention or treatment.

Structural Engineer

A licensed professional who designs structural systems for buildings, ensuring they safely resist loads. Required for most ADU projects in California.

Stucco

A cement-based exterior plaster applied over lath, popular in California for durability and fire resistance. Requires proper flashing and weep screeds.

Stud

Vertical framing member in walls, typically 2x4 or 2x6 lumber or steel. Standard spacing is 16" or 24" on center depending on structural and insulation requirements.

Subcontractor

A specialty contractor hired by the general contractor for specific work such as electrical, plumbing, HVAC, or roofing. Must be properly licensed.

Subfloor

The structural floor sheathing installed over floor joists, providing a base for finished flooring. Typically plywood or OSB panels.

Subpanel

A secondary electrical panel fed from the main panel, distributing power to circuits in a portion of the building. Common for ADU electrical service.

Sump Pump

A pump that removes water collected in a sump basin, typically in basements or crawl spaces prone to flooding. Helps keep foundations dry.

Survey

A professional measurement and mapping of property boundaries and features. May be required to verify setbacks and property line locations for ADU permits.

Scuttle

An access opening to an attic or roof, typically covered by a removable panel or hatch. Required for access to attic spaces and equipment.

Service Panel

The main electrical distribution panel containing the main breaker and branch circuit breakers. Location and capacity are key factors in ADU electrical design.

Shim

A thin wedge used to fill gaps and level or plumb components during installation. Made of wood, plastic, or metal depending on application.

Shoe Molding

A small molding at the junction of the baseboard and floor, covering expansion gaps and providing a finished appearance.

Shutoff Valve

A valve that stops water or gas flow to fixtures or appliances. Individual shutoffs are required at each fixture for isolation during repairs.

Sister (Framing)

To attach a new framing member alongside an existing one for reinforcement. Common repair technique for damaged joists or studs.

Sleeper

Wood strips laid over concrete to create a nailing surface for finish flooring. Provides a level surface and allows for insulation beneath.

Smart Home

Technology integration for automated control of lighting, HVAC, security, and appliances. Increasingly popular in modern ADU design.

Snap-In (Plumbing)

A pipe support or clamp that clips onto framing members without tools. Simplifies installation of plumbing supply and drain lines.

Soaker (Flashing)

Metal flashing pieces interwoven with roofing material at wall-to-roof junctions. Prevents water infiltration at critical transitions.

Sole Plate

The bottom horizontal member of a wall frame, resting on the subfloor or sill plate. Also called the bottom plate.

Space Planning

The organization of interior spaces for optimal function and flow. Critical for efficient ADU layouts that maximize limited square footage.

Spandrel

The triangular space between the curve of an arch and the surrounding structure. Also refers to panels between floor levels on multi-story buildings.

Spec Home

A house built on speculation without a specific buyer. Prefab ADU manufacturers often display spec units to showcase their designs.

Splice

A connection joining two structural members or wires end-to-end. Requires proper technique and, for electrical, appropriate junction boxes.

Split System

An HVAC system with separate indoor and outdoor components connected by refrigerant lines. Includes mini-splits popular for ADUs.

Sprinkler System (Fire)

An automatic fire suppression system. May be required for ADUs in certain conditions, such as those attached to the primary dwelling.

Stack Effect

Air movement in buildings due to temperature differences between inside and outside. Warm air rises, creating pressure differences that affect ventilation.

Staging Area

A designated space on site for storing materials and equipment during construction. Planning staging is important for ADU projects with limited space.

T

Tankless Water Heater

An on-demand water heating system that heats water only when needed, saving space and energy. Popular choice for ADUs due to compact size.

Temporary Power

Electrical service established for construction purposes before permanent service is installed. Provides power for tools and equipment during building.

Title 24

California Building Standards Code, including energy efficiency (Part 6), CALGreen (Part 11), and accessibility requirements. ADUs must comply with applicable sections.

Top Plate

Horizontal framing member at the top of wall studs. Double top plates are typical in load-bearing walls; single plates may be used in non-bearing walls.

Topography

The shape and features of land surfaces, including elevation changes. Affects ADU placement, foundation design, drainage, and construction costs.

Tract Map

A recorded document showing the division of land into lots. May contain conditions or restrictions affecting ADU construction.

Tread

The horizontal portion of a stair step. Building codes specify minimum tread depth (typically 10") and require uniform treads in a flight of stairs.

Trim

Finish moldings applied to interior and exterior surfaces, including baseboards, door and window casings, crown molding, and corner boards.

Truss

A prefabricated structural frame typically used for roofs and floors, composed of wood or steel members in a triangulated configuration. Faster to install than stick-built framing.

T-Bar Ceiling

A suspended ceiling system using T-shaped metal tracks to support acoustic tiles. Provides easy access to utilities above but reduces ceiling height.

Takeoff (Quantity)

The process of measuring quantities of materials needed from construction drawings. Used for cost estimating and ordering materials.

Tempered Glass

Heat-treated glass that breaks into small, safer fragments. Required in locations prone to impact, including doors, near bathtubs, and low windows.

Thermostat

A device controlling HVAC systems to maintain desired temperature. Programmable and smart thermostats help meet California energy code requirements.

Threshold

The strip at the bottom of an exterior door providing a seal against weather. Accessible designs require low thresholds (1/2" maximum).

Tie-Down

Metal hardware connecting walls to foundations to resist uplift forces. Required by building codes, especially in high-wind and seismic zones.

Tile

Ceramic, porcelain, or stone units for floors, walls, and countertops. Requires proper substrate preparation and waterproofing in wet areas.

Tongue and Groove

An interlocking joint system where one board's projecting edge fits into an adjacent board's groove. Used for flooring, paneling, and decking.

TPO Roofing

Thermoplastic polyolefin membrane roofing for flat roofs. Energy-efficient white surface and heat-welded seams make it popular for modern ADUs.

U

U-Factor

A measure of heat flow through building materials, the inverse of R-value. Lower U-factors indicate better insulating performance. Used for window ratings.

Underfloor

The space beneath a raised floor, providing access for utilities and requiring proper ventilation and vapor barriers in crawl space configurations.

Underlayment

A layer between the structural substrate and finish material, such as roof felt under shingles or plywood under finished flooring.

Unpermitted Construction

Work done without required permits, creating liability and complications for future sales or modifications. May need to be legalized before adding an ADU.

Urban Lot Split

A subdivision process created by SB 9 allowing qualifying single-family parcels in urban areas to be divided into two lots, each potentially hosting additional units.

Utility Connection

The point where building systems connect to public utilities (water, sewer, electric, gas). ADU connections may be new or tap existing service.

Ufer Ground

An electrical grounding system using rebar in concrete foundations. Provides excellent grounding and is required in new California construction.

Unfinished Space

Areas without interior finishes such as attics, crawl spaces, and garages. Conversion to habitable space requires finishing and may create ADU opportunities.

Universal Design

Design principles creating spaces usable by all people regardless of age or ability. Includes wider doors, lever handles, and accessible bathrooms.

Upzoning

Changing zoning to allow more intensive use or higher density. California's ADU laws effectively upzone single-family properties for accessory units.

V

Valley

The internal angle where two roof slopes meet, channeling water to gutters or downspouts. Requires careful flashing to prevent leaks.

Vapor Barrier

Material that resists moisture vapor diffusion through walls, floors, and ceilings. Placement depends on climate; in California typically on the warm side of insulation.

Variance

An exception to zoning regulations granted when strict compliance creates undue hardship. California's ADU laws reduce the need for variances by establishing statewide standards.

Vent Stack

A vertical pipe in the plumbing system that extends through the roof, allowing air into the drainage system and releasing sewer gases safely.

Ventilation

The exchange of indoor and outdoor air to maintain air quality. Required in habitable rooms, bathrooms, and kitchens through operable windows or mechanical systems.

VHFHSZ (Very High Fire Hazard Severity Zone)

Areas designated as having extreme fire risk, requiring enhanced fire-resistant construction. May affect ADU materials, roof covering, and exterior finish choices.

Value Engineering

The process of analyzing a design to reduce costs while maintaining quality and function. Common in ADU projects to meet budget constraints.

Vanity

A bathroom cabinet with a sink, providing storage and counter space. Compact vanities are essential for efficient ADU bathroom design.

Vent

An opening or pipe allowing air movement. Includes plumbing vents, attic vents, and exhaust vents, each with specific code requirements.

Vinyl Flooring

Synthetic flooring material available in sheets, tiles, or planks. Water-resistant, durable, and affordable, making it popular for ADUs.

Volt

A unit of electrical pressure. Residential circuits are typically 120 volts; heavy appliances like dryers and ranges use 240-volt circuits.

W

Water Heater

An appliance for heating domestic water. ADUs may have dedicated water heaters (tank or tankless) or share systems with the primary dwelling.

Water Meter

A device measuring water consumption. California prohibits requiring separate water meters for ADUs, allowing shared service with the primary dwelling.

Water Service

The pipe connecting a property to the public water main. ADUs typically tap into existing service; new connections may require upsizing.

Waterproofing

Treatments and materials preventing water penetration into building assemblies. Critical for foundations, below-grade walls, and wet areas like bathrooms.

Weatherstripping

Sealing material applied around doors and windows to prevent air and water infiltration. Essential for energy efficiency and comfort.

Weep Screed

A metal flashing at the bottom of stucco walls that allows moisture to drain while providing a clean termination point above grade.

Wiring

Electrical cables and conductors in a building. Most residential wiring is nonmetallic sheathed cable (Romex) in protected locations or conduit where exposed.

Work Triangle

A kitchen design concept measuring the distance between refrigerator, sink, and range. Optimal layout keeps the total distance between 13 and 26 feet.

Wainscoting

Wood paneling or other material covering the lower portion of walls. Provides protection and decorative detail in traditional or transitional designs.

Warranty

A guarantee of work quality and materials. Contractors provide workmanship warranties; manufacturers warranty products. Document and understand coverage.

Water Pressure

The force of water in supply lines, measured in PSI. Adequate pressure (40-80 PSI) ensures proper fixture operation; pressure regulators may be needed.

Wet Wall

A wall containing water supply and drain lines, typically serving bathrooms and kitchens. Back-to-back wet walls reduce plumbing costs.

Window Schedule

A document listing all windows with sizes, types, locations, and specifications. Required for energy code compliance and permit applications.

Wire Gauge

The size of electrical wire, with lower numbers indicating larger wire. Common residential gauges are 14, 12, and 10 AWG for 15, 20, and 30-amp circuits.

Wood Frame Construction

Building using dimensional lumber for structural framing. The dominant construction method for residential buildings including ADUs in California.

X

X-Bracing

Diagonal cross-bracing that provides lateral stability to structural frames. Common in steel construction and under raised floors.

Xeriscaping

Landscaping designed to minimize water use through drought-tolerant plants and efficient irrigation. Encouraged or required in many California jurisdictions.

Y

Yard

In zoning terms, the open space between a building and property lines. Front, side, and rear yards are defined by setback requirements.

Yoke (Electrical)

The metal frame holding electrical switches and receptacles in an outlet box. Also called a strap or mounting bracket.

Z

Zero Lot Line

Construction that extends to the property line with no side setback. Typically requires fire-rated wall construction and may be allowed for certain ADU configurations.

Zoning

Local regulations dividing land into districts with specific permitted uses and development standards. California ADU laws override some local zoning restrictions.

Zoning Clearance

Verification that a proposed project complies with zoning regulations. Often required before or concurrent with building permit approval.

Zone (HVAC)

A section of a building with independent temperature control. ADUs typically constitute a single zone with dedicated HVAC equipment.

Z-Flashing

Metal flashing with a Z-shaped profile used at horizontal joints in siding to direct water away from wall assemblies.