ADU Housing Glossary

Last reviewed: November 1, 2026. Your comprehensive guide to ADU terminology

General ADU Terms

Accessory Dwelling Unit (ADU)

A secondary residential unit on the same property as a primary home, often used for rental or family housing. For example, a backyard cottage can serve as an ADU for tenants.

Junior Accessory Dwelling Unit (JADU)

A junior ADU is no more than 500 square feet of interior livable space, built within a single-family home. It's perfect for elderly relatives, like converting a bedroom into a compact studio.

ADU Zoning Regulations

Local laws governing where and how ADUs can be built, including size or parking rules. Some areas require one parking space per ADU.

ADU Permits

Official approvals needed to legally construct an ADU. A building permit ensures compliance with safety codes, for instance.

ADU Plancheck Fees

Fees for reviewing ADU plans to meet local standards. These are paid before construction starts and vary by city.

ADU Permit Fees

Costs for obtaining construction permits, covering administrative expenses. These differ depending on the jurisdiction.

ADU Impact Fees

Charges that help pay for public facilities. As of November 1, 2026, an ADU with 750 square feet of interior livable space or less is not charged an impact fee. A larger ADU is charged in proportion to the main home. Utility connection charges are not impact fees (Gov. Code §66311.5). Starting January 1, 2027, SB 1117 (Cervantes), Chapter 809, Statutes of 2026 keeps the no-fee rule for an ADU of 750 square feet of interior livable space or less, and for a junior ADU of 500 square feet or less. On a lot with up to two ADUs, an impact fee on a larger ADU is still charged in proportion to the main home, and only on the square feet above 750. A lot with more than two ADUs keeps today's proportional rule on the whole unit. The change applies to charter cities. It does not set a dollar amount, and connection charges stay separate. Local ordinances have to follow it on that date. Ask your city before you budget a fee. The March 2026 HCD handbook does not cover this bill yet. See the 2026 law update.

ADU Parking Requirements

A city cannot require more than one space per ADU or bedroom, whichever is less, and cannot require parking within a half-mile walk of public transit or for an ADU inside existing space (Gov. Code §§66314 and 66322). The other exemptions, including car share and a converted garage, are in the setback and parking guide.

ADU Pedestrian Access

Requirements for safe, accessible pathways to the ADU. This could mean adding a sidewalk to the entrance.

ADU Property Tax Implications

The impact of an ADU on property taxes, which may rise with added value. A $100,000 ADU could increase taxes based on local rates.

Utilities and Connections

ADU Water Utility Connection

Linking the ADU to the water supply for clean water access. It might tie into the main house's water line for simplicity.

ADU Sewer Utility Connection

Connecting the ADU to the sewage system for waste disposal. This ensures compliance with health standards.

ADU Electric Utility Connection

The electrical setup for the ADU, either linked to the main house or separate. It's like wiring a small apartment.

ADU Gas Utility Connection

Connecting to gas for heating or cooking. This powers appliances like stoves in the ADU.

Separate Utility Meters for ADU

Individual meters to track ADU utilities separately. This allows tenants to pay their own electric bills, for example.

ADU Utility Upgrades

Improvements to existing utilities to support the ADU. Upgrading an electrical panel might be needed for added demand.

ADU Water Heater

A dedicated unit providing hot water for the ADU. A tankless heater saves space and energy.

ADU Internet Connection

Setting up internet access for the ADU, often via Wi-Fi or a separate line. This ensures tenant connectivity.

ADU Stormwater Management

Systems to handle runoff from the ADU, like gutters. This prevents flooding on the property.

ADU Utility Trenching

Digging trenches to install underground utility lines. This connects water or power to a detached ADU.

Construction Methods and Materials

Wood-Frame ADU Construction

Using wood as the main structural material. It's cost-effective and widely used in residential building.

Modular ADU Construction

Building the ADU off-site in sections for quick assembly. A pre-made shed delivered in a day is an example.

Pre-Fab ADU Construction

Using pre-manufactured units installed on-site. It's like ordering a ready-made tiny home.

Slab Foundation

A concrete base supporting the ADU. It's common in stable-soil areas, like a concrete patio.

Crawl Space Foundation

A raised foundation with space underneath for maintenance. It's like a deck with storage below.

Asphalt Shingle Roofing

Affordable roofing made from asphalt-fiberglass material. It's standard on many suburban homes.

Metal Roofing

Durable, weather-resistant roofing from metal sheets. It resembles barn-style roofs.

Vinyl Siding

Low-maintenance exterior cladding in various colors. It's like plastic panels on modern homes.

Structural Insulated Panels (SIPs)

Pre-made panels with foam insulation for walls and roofs. They're like insulated sandwich boards for efficiency.

ADU Windows and Doors

Selecting energy-efficient windows and secure doors. Double-glazed windows cut heat loss, for instance.

Costs and Financing

ADU Construction Costs

Total expenses for building an ADU, including labor and materials. A 600-square-foot unit might cost $200,000.

ADU Architect Fees

Charges for designing the ADU, often a percentage of costs. Illustration only: a basic design might cost $10,000.

ADU City Fees

Fees for permits and inspections by the city. Illustration only: these might total $5,000 for processing.

ADU Financing (HELOC)

A Home Equity Line of Credit to fund the ADU. It's like a credit card backed by your home.

ADU Rental Income

Earnings from renting the ADU to offset costs. Illustration only: a tenant might pay $2,000 monthly.

ADU Grants

Government funds aimed at ADU costs. CalHFA's ADU Grant reimbursed up to $40,000 in pre-development costs, but the latest round was fully allocated on December 28, 2023 and is not open as of October 22, 2026.

ADU Tax Credits

Incentives reducing tax liability for building an ADU. Energy-efficient ADUs might qualify.

ADU Investment Returns

Financial gains from the ADU, like rental income or value increase. Illustration only: it could yield a 5% return annually.

ADU Financing (Construction Loan)

A short-term loan for building, later converted to a mortgage. It's like a bridge loan for projects.

ADU Financial Incentives

Rebates or waived fees to encourage ADU building.

Legal and Regulatory

Legalizing Unpermitted ADUs

Obtaining permits for an unapproved ADU retroactively. This might involve adding fire safety features.

ADU Structural Support

The framework ensuring the ADU's stability per codes. Load-bearing walls are key for two-story units.

ADU Tax Implications

How an ADU affects taxes, including rental income reporting. A $24,000 yearly rental might increase tax obligations.

ADU Laws and Regulations

Legal rules governing ADU construction. California allows ADUs on single-family lots, for example.

ADU Setbacks

How far the unit sits from a lot line. For a new ADU, a city cannot require more than 4 feet from the side and rear lot lines. A conversion inside existing walls does not take a new setback (Gov. Code §66314). Height, the 800-square-foot floor, and parking are in the setback and parking guide.

ADU Size Limits

A detached ADU cannot exceed 1,200 square feet. A city also cannot set a maximum below 850 square feet of interior livable space, or below 1,000 square feet if the ADU has more than one bedroom (Gov. Code §§66314 and 66321).

ADU Parking Requirements

The statewide cap is one space per ADU or per bedroom, whichever is less. Several situations, including a half-mile walk to public transit, require zero spaces. See the setback and parking guide.

ADU Owner-Occupancy Requirements

A city cannot require the owner to live on the property for an ADU (Gov. Code §66315). A JADU requires owner occupancy only when it shares sanitation facilities with the main home (Gov. Code §66333).

ADU HOA Rules

Homeowners Association restrictions on ADUs. They might limit rentals or require design approval.

ADU Encroachment Permits

Permits for ADUs extending beyond property lines. This applies to building over a shared driveway.

Design and Planning

ADU Site Assessment

Evaluating the property for ADU feasibility. It checks lot size and zoning suitability.

ADU Architectural Design

Designing the ADU's layout and look. A small open-plan studio fits tight lots well.

ADU Floor Plans

Diagrams showing the ADU's layout. A 400-square-foot unit might include a kitchen and bedroom.

ADU Energy Efficiency

Features reducing energy use, like insulation. LED lights save power in small spaces.

ADU Accessibility

Design for disability access, like ramps. ADA-compliant bathrooms aid seniors.

ADU Sustainability

Eco-friendly materials and practices. Solar panels cut energy costs sustainably.

ADU Permitting Process

Steps to get construction permits. This includes submitting plans and attending reviews.

ADU Feasibility Study

Analysis of practicality and benefits. It weighs costs against rental income potential.

ADU Elevation Drawings

External views of the ADU's design. They show window and door placement.

ADU Material Selection

Choosing durable, cost-effective materials. Vinyl siding is low-maintenance, for example.

Maintenance and Upkeep

ADU Maintenance Tasks

Routine upkeep like gutter cleaning. Annual roof checks prevent leaks.

ADU Pest Control

Preventing infestations with sealing or traps. Termite control protects wood structures.

ADU Roof Maintenance

Keeping the roof intact, like replacing shingles. Post-storm inspections catch damage early.

ADU Landscaping

Maintaining outdoor areas around the ADU. Adding shrubs boosts curb appeal.

ADU Exterior Painting

Painting to protect against weather. Refreshing stucco every few years maintains appearance.

ADU HVAC Maintenance

Servicing heating and cooling systems. Annual filter changes keep air quality high.

ADU Plumbing Maintenance

Checking pipes and fixtures for issues. Fixing leaks prevents water waste.

ADU Electrical Maintenance

Inspecting wiring and outlets for safety. Replacing old switches avoids hazards.

ADU Window Cleaning

Keeping windows clear for light and looks. Annual cleaning enhances efficiency.

ADU Gutter Maintenance

Clearing debris from gutters to prevent overflow. This protects the foundation.

Interior Design and Finishes

ADU Kitchen Design

Planning a functional kitchen in limited space. A compact island adds storage.

ADU Bathroom Design

Creating a practical bathroom layout. A walk-in shower suits small units.

ADU Flooring Options

Choosing durable flooring like hardwood. Laminate offers a budget-friendly alternative.

ADU Lighting Design

Arranging lights for function and mood. Pendant lights work well in kitchens.

ADU Painting and Wall Finishes

Selecting paint or wallpaper for walls. Neutral tones brighten small spaces.

ADU Storage Solutions

Maximizing space with built-ins or shelves. Under-bed storage fits tight rooms.

ADU Countertop Materials

Picking durable surfaces like quartz. It's low-maintenance for kitchens.

ADU Cabinetry

Installing cabinets for storage and style. White cabinets open up small areas.

ADU Window Treatments

Adding blinds or curtains for privacy. Blackout shades help with sleep.

ADU Interior Doors

Choosing doors for space and design. Pocket doors save room in tight spots.

Safety and Security

ADU Fire Safety Features

Installing detectors and extinguishers. Kitchen smoke alarms reduce fire risks.

ADU Security Systems

Using alarms or cameras for safety. A smart doorbell monitors visitors.

ADU Emergency Preparedness

Planning for crises with exits and kits. A first-aid kit is a basic must-have.

ADU Smoke Detectors

Devices alerting to smoke or fire. Placing one in each bedroom is standard.

ADU Carbon Monoxide Detectors

Sensors for detecting CO gas. They're vital near gas appliances.

ADU Exterior Lighting

Lights deterring intruders and aiding visibility. Motion-sensor lights are effective.

ADU Locks and Deadbolts

Securing doors with strong locks. Deadbolts add extra protection.

ADU Fire Escape Plan

A mapped route for safe evacuation. It includes two exits per room.

ADU Window Security

Reinforcing windows against break-ins. Locks or bars enhance safety.

ADU Fencing

Adding a fence for privacy and security. A 6-foot fence deters trespassers.

Marketing and Rental

ADU Short-Term Rentals (Airbnb)

Renting the ADU briefly via platforms like Airbnb. Some areas limit stays to 30 days.

ADU Long-Term Rentals

Leasing the ADU for extended periods. Illustration only: a year-long lease might be $2,000 monthly.

ADU Property Management

Handling rentals, repairs, and tenants. A manager simplifies tenant screening.

ADU Rental Pricing

Setting rent based on market rates. A 500-square-foot ADU might fetch $1,800.

ADU Tenant Screening

Checking backgrounds for reliable renters. Credit checks ensure payment reliability.

ADU Marketing Strategies

Promoting the ADU via listings or signs. Online platforms like Zillow attract tenants.

ADU Lease Agreements

Legal contracts outlining rental terms. They specify rent and maintenance duties.

ADU Occupancy Limits

Rules on how many people can live in the ADU. A 400-square-foot unit might cap at two.

ADU Rental Insurance

Insurance covering rental-related risks. It protects against tenant damage.

ADU Open House

Hosting events to showcase the ADU. A weekend showing can attract renters.

Professionals and Services

ADU General Contractors

Professionals overseeing the ADU construction process, coordinating all trades. They manage everything from permits to final inspections, for example.

ADU Architects

People who draw ADU plans. They check that the design meets building codes and the owner's needs.

ADU Structural Engineers

Engineers verifying the ADU's structural integrity. They might design load-bearing elements for safety.

ADU Mechanical Engineers

Specialists designing HVAC and plumbing systems. They ensure efficient heating and cooling.

ADU Electrical Engineers

Professionals planning the electrical layout. They size circuits for appliances safely.

ADU Inspectors

Officials checking the ADU for code compliance. They review framing and electrical work.

ADU Subcontractors

Specialized workers like plumbers or roofers. They handle specific construction tasks.

ADU Construction Managers

Overseeing the build's timeline and budget. They coordinate subcontractors for efficiency.

ADU Designers

Creating interior or aesthetic plans. They select finishes and layouts for appeal.

ADU Permit Expediters

People who help file permit paperwork with the local building department.