ADU.APP · ACCESSORY DWELLING UNIT PLANNING
Plan your ADU
with ADU.app.
ADU.app helps homeowners plan accessory dwelling units—small homes on the same property as a main residence. Estimate ADU costs, compare building options and prepare for local permits with free tools and guides.
Free planning tools · Estimates, not contractor quotes
SMALL HOME. BIGGER POSSIBILITY.
Plan an accessory dwelling unit, one decision at a time.
An accessory dwelling unit is a separate home on the same property as a main residence. ADU.app helps homeowners compare building approaches, estimate a complete project budget and prepare questions for local planning departments. Start with your property and intended use, then check costs and permits before committing to a design.
EXPLORE ADU.APP
From first question to a confident plan.
A focused set of tools and guides for the decisions that matter most.
Check your property
Identify the local permit authority. Ask about allowed uses, size, setbacks, access and utility capacity before paying for plans.
Explore 02⌂Compare ADU types
Compare a new detached home, an addition or a conversion against your space, privacy needs and existing structure.
Explore 03$Estimate the budget
Include design, fees, sitework and utilities as well as construction. Replace assumptions with complete written quotes.
Explore 04✓Prepare for permits
Confirm the required drawings, supporting reports, review steps and fees with the agency responsible for your address.
ExploreFIND YOUR FIT
A small home can take many forms.
Start with how you want to live, then choose the building approach that suits the property.
01Detached ADU
Example sizes: 450–1,200 sq ft · Rental income, family, long-term flexibility
Explore the type
02Attached ADU
Example sizes: 400–1,000 sq ft · Caregiving, guest space, close family living
Explore the type
03Garage Conversion
Example sizes: 300–700 sq ft · Smaller budgets and efficient footprints
Explore the typeADU KNOWLEDGE LIBRARY
Research the decisions behind the design.
Original, practical guides for homeowners comparing cost, permits, construction, layouts, and rental potential.
ADU Cost Guide
Understand the major costs of building an ADU, from design and permits to site work, utilities, construction, contingency, and financing.
Read guide 02ADU typesDetached vs. Attached ADU
Compare detached and attached ADUs by privacy, cost, construction complexity, utilities, property fit, rental use, and long-term flexibility.
Read guide 03ConstructionPrefab ADU Guide
Learn how prefab ADUs work, what factory construction includes, which site costs remain, and what to ask before choosing a modular or panelized home.
Read guide 04RegulationsADU Permit Checklist
Use this ADU permit checklist to research zoning, size, setbacks, utilities, fire access, drawings, fees, plan review, and final inspections.
Read guideLATEST ADU RESEARCH
Focused answers to the questions people search.
Current articles pair concise answers with transparent examples, practical checklists, comparison tables, and official sources.
California rulesCalifornia ADU Laws 2026
A homeowner-focused overview of California ADU laws in 2026, including the state framework, local review, property checks, permits, and official sources.
Read article
Cost planningADU Cost per Square Foot
Compare published San Diego ADU costs with transparent calculator examples. Understand construction-only vs. project budgets, exclusions and cost per square foot.
Read article
Small ADU budget500 Sq Ft ADU Cost
Build an early 500 sq ft ADU budget with transparent examples for detached, attached, garage-conversion, and prefab approaches.
Read articleLOCAL ADU RESEARCH
Start with the rules that shape your property.
State law creates the framework, but local agencies review the actual site. Use these location guides to organize the right questions before design begins.
PROJECT INSPIRATION
Ideas for different backyards and different lives.
Use the concepts to compare scale and character, then validate any direction against the property, rules and complete budget.
REGULATIONS, WITHOUT THE OVERWHELM
Know what to verify before design begins.
Confirm jurisdiction, allowable type, size, height, setbacks, access, utilities, parking and permit steps before committing to drawings.
Six questions for a stronger first conversation.
01 Is an ADU allowed on this property?
02 What size and height limits apply?
03 Which setbacks shape placement?
A CLEARER START
Questions homeowners ask first.
Use these basics as a starting point, then confirm property-specific requirements with qualified local professionals.
01What is ADU.app?+
ADU.app is an educational website with a free accessory dwelling unit cost calculator, building-type comparisons, planning guides and design ideas. It helps homeowners prepare questions and budgets; it does not supply contractor quotes or determine whether a property qualifies for an ADU.
02What does ADU stand for?+
Accessory dwelling unit—a secondary, independent residence located on the same property as a primary home.
03What can an ADU be used for?+
Common uses include multigenerational living, guest space, long-term rental income, a downsized owner residence, or flexible work and care space.
04How much does an ADU cost?+
The answer depends on size, type, access, utilities, site conditions, finishes, design, permitting, and local labor. Use the calculator for an early planning range.
05Do I need local approval?+
Usually, yes. Planning, building, utility, fire, environmental, and other approvals can apply. Always confirm current requirements with your local authority and licensed professionals.
SOURCES AND LIMITS
Know what your plan is based on.
ADU.app publishes educational guides and free planning tools with AI-assisted research and writing. No independent professional review is claimed.
The calculator uses published editorial assumptions, not verified construction prices for every city. Official planning sources help you check rules; choosing a location does not establish that an ADU is permitted on your property.
YOUR PROPERTY, REIMAGINED