Edit with
QuiPlans — Licensed Structural Engineers · PE-Stamped Plans in 25 States
QuiPlans — 7,000+ Homeowners Served · Join the QuiPlans Community
QuiPlans — Permit Success Guarantee · Plans Accepted by Building Departments
QuiPlans — Permit-Ready Plans from $1,997 · Free ADU Floor Plan Available
QuiPlans — Plans Delivered in Days — Not Months · No Architect Required
QuiPlans — 4.9/5 Average Rating · Trusted by Builders Nationwide
Everything you need to understand the ADU process — from zoning regulations and permits to construction, financing, and working with builders.
No fluff. No sales pitches. Just the knowledge you need to make informed decisions about your property.
The complete landscape of accessory dwelling units — types, legal context, and what they mean for your property.
An Accessory Dwelling Unit (ADU) is a self-contained living space on the same lot as a single-family home. It has its own kitchen, bathroom, sleeping area, and entrance — making it a fully independent dwelling, not just a room addition. ADUs are known by many regional names: granny flats (California), backyard cottages (Pacific Northwest), in-law suites (Northeast), casitas (Southwest/Texas), garage apartments, and laneway houses (Canada). Despite the different names, the concept is the same: a second, smaller home on your property. The key legal distinction is that an ADU is subordinate to the main house. It cannot be sold separately from the primary residence (in most states). It's part of your property, not a separate parcel.
1. DETACHED ADU — A standalone structure built in your backyard. This is the most common and flexible type. You can place it anywhere zoning allows, design it to match or contrast with your main house, and size it from 200–1,200 sqft. Typical cost: $100K–$250K. 2. ATTACHED ADU — An addition that shares at least one wall with your main house. Often built over a garage or as a wing extension. Less expensive than detached (shared foundation/wall), and can be ideal when backyard space is limited. Typical cost: $80K–$180K. 3. GARAGE CONVERSION — Transforming an existing attached or detached garage into living space. Often the most affordable path since the structure already exists. You're reusing the foundation, walls, and roof. Typical cost: $40K–$90K. Watch out: you may lose parking, and some cities require replacement parking. 4. JADU (Junior ADU) — A small unit (max 500 sqft) created within the existing footprint of your home. Think of it as converting a bedroom or wing into a self-contained unit. Lowest cost option. Typical cost: $30K–$80K. 5. BASEMENT ADU — Converting an existing basement into a livable unit. Requires egress windows, ceiling height clearance (usually 7ft minimum), and moisture management. Popular in older homes with full basements. Typical cost: $50K–$120K.
A detailed, realistic walkthrough of every phase — with timelines, costs, and what to expect at each stage.
Before spending a dollar on design, you need to answer: Can I legally build an ADU on my property? KEY TASKS: • Check your zoning — Look up your property on your city's zoning map. You're looking for whether ADUs are permitted, and if so, what restrictions apply (size, height, setback, parking). • Check your lot — Measure your lot size, existing coverage (house + driveway + garage), and available backyard space. Most cities cap total lot coverage at 40–60%. • Verify utilities — Can your existing water, sewer, electrical, and gas lines support a second unit? You may need to upgrade your panel or run new connections. • Check HOA rules — If you live in an HOA, review the CC&Rs. Some HOAs prohibit ADUs entirely (though state law may override this). • Order a feasibility report — A professional review of your property that checks zoning, setbacks, utility capacity, and buildable area. Costs $300–$500 and can save you from a $100K+ mistake. WHAT TO WATCH FOR: • Easements, utility lines, or drainage areas that reduce your buildable area • Setback requirements that may make your lot too small • Impact fees (some cities charge $5,000–$20,000 in school/traffic fees) • Soil conditions that may require expensive foundation work TYPICAL COST: $0–$500 (DIY research is free; professional feasibility report ~$350)
Once you've confirmed your property can support an ADU, the next step is getting plans drawn up. KEY TASKS: • Choose your ADU type — Detached, attached, garage conversion, or JADU. This affects everything from cost to timeline. • Select a floor plan — Either buy pre-designed plans (faster, cheaper) or hire an architect for custom design (slower, more expensive, but tailored to your lot). • Get structural engineering — If your plans need to be stamped by a Professional Engineer (PE), this is where that happens. Engineering includes foundation design, framing, lateral/wind/seismic analysis, and connection details. • Complete MEP plans — Mechanical, Electrical, and Plumbing drawings showing how utilities will be routed. • Energy compliance — Many states (especially California with Title 24) require energy calculations proving the unit meets efficiency standards. PLAN TYPES EXPLAINED: • Concept plans ($0–$300): Basic layout for visualization. Not for permits. • Architectural plans ($1,000–$3,000): Detailed drawings with dimensions, schedules, and elevations. Good for contractor bidding but NOT for permits. • Permit-ready plans ($1,300–$3,500): Architectural + structural + MEP, all PE-stamped. Ready to submit to the building department. TYPICAL COST: $1,300–$5,000 (pre-designed) or $8,000–$25,000 (custom architect) TYPICAL TIMELINE: 2–6 weeks (pre-designed) or 8–16 weeks (custom)
Real regulatory knowledge — setbacks, height limits, lot coverage, parking, owner-occupancy, and state-by-state differences.
Zoning is the set of rules your city uses to control what can be built where. For ADUs, the key zoning parameters are: • SETBACKS: How far the ADU must be from property lines. Typical: 4–5 ft side/rear, 20 ft front. Some cities allow reduced setbacks (0–2 ft) for detached ADUs under 800 sqft. • HEIGHT LIMITS: Maximum building height. Typical: 16 ft for one-story detached ADUs. Some cities allow 24–28 ft for two-story. JADUs and attached ADUs may follow the main house height limit. • LOT COVERAGE: Maximum percentage of your lot that can be covered by structures. Typical: 40–60% combined (main house + ADU + garage + any other structures). • MINIMUM LOT SIZE: Some cities require a minimum lot size (e.g., 5,000 sqft) to qualify for an ADU. • MAXIMUM ADU SIZE: Usually capped at 800–1,200 sqft for detached ADUs, or 50% of the main house's living area (whichever is smaller). These numbers vary by city. You must look up the specific zoning for your property — don't assume neighboring cities have the same rules.
Parking is one of the most common obstacles for ADU projects. Here's what to expect: CALIFORNIA (most permissive): • No additional parking required for ADUs within ½ mile of transit (bus or rail) • No parking required for ADUs within an architecturally/historically significant district • No parking required for garage conversions or JADUs (since you're not adding a new unit, just converting) • Otherwise: 1 off-street parking space per ADU bedroom (tandem spaces OK) TEXAS (varies by city): • Austin: No additional parking required for ADUs in most zones • Dallas: 1 space required per ADU • Houston: Varies by lot size and zone • Many suburbs: 2 spaces required FLORIDA: • State law allows local control; most cities require 1 space • No parking requirement if the property is within ¼ mile of a transit stop GENERAL TRENDS: • Parking requirements are being relaxed nationwide • Tandem parking (one car behind another) is usually accepted • Driveway spaces can count toward the requirement • If you're converting a garage, you may need to provide replacement parking WHAT TO CHECK: Look up your city's municipal code (usually online) and search for 'accessory dwelling unit' or 'secondary unit' or 'guest house.'
Real cost data by phase, size, and location — with the factors that drive costs up or down.
Here's what homeowners actually pay (2026 data, national averages): STUDIO / 400 SQFT: • Garage conversion: $40,000–$80,000 • New detached build: $80,000–$140,000 • High-cost markets (CA Bay Area, NYC): $120,000–$200,000 1-BEDROOM / 550 SQFT: • Garage conversion: $50,000–$95,000 • New detached build: $110,000–$190,000 • High-cost markets: $160,000–$280,000 2-BEDROOM / 750 SQFT: • New detached build: $150,000–$260,000 • High-cost markets: $200,000–$350,000+ These numbers include everything: design, permits, site prep, construction, and finishes. They assume mid-range finishes (not luxury, not budget). If you want luxury finishes, add 20–40%. If you're doing a lot of work yourself (owner-builder), you can save 15–30% on labor.
Understanding the cost breakdown helps you see where you can save: DESIGN & ENGINEERING (5–8% of total budget): • Plans: $1,300–$3,500 (pre-designed) or $8,000–$25,000 (custom architect) • Structural engineering: Included in permit-ready plans or $3,000–$8,000 separately • MEP engineering: $1,500–$4,000 (if separate) PERMITS & FEES (5–10%): • Building permit: $1,500–$5,000 • Impact/school fees: $0–$15,000 • Plan check fees: $500–$2,000 • Utility connection fees: $1,000–$10,000 SITE PREP & FOUNDATION (15–20%): • Grading/excavation: $3,000–$10,000 • Foundation: $8,000–$30,000 • Utility trenching: $3,000–$10,000 • Demolition (if applicable): $2,000–$8,000 CONSTRUCTION — SHELL (20–25%): • Framing: $10,000–$30,000 • Roofing: $4,000–$12,000 • Windows & exterior doors: $3,000–$8,000 • Siding/exterior: $4,000–$12,000 MEP SYSTEMS (15–20%): • Electrical: $5,000–$15,000 • Plumbing: $5,000–$15,000 • HVAC: $4,000–$10,000 INTERIOR FINISHES (20–25%): • Insulation & drywall: $5,000–$15,000 • Flooring: $3,000–$10,000 • Cabinets & countertops: $4,000–$15,000 • Paint & trim: $3,000–$8,000 • Fixtures & appliances: $3,000–$12,000
From HELOCs to construction loans to ADU-specific programs — which financing path is right for you.
A HELOC lets you borrow against your home's equity at a variable interest rate. HOW IT WORKS: • You're approved for a maximum credit line (typically up to 80–85% of your home's value minus your mortgage balance) • You draw funds as needed during construction • You pay interest only on what you've drawn during the draw period (usually 10 years) • After the draw period, you repay principal + interest over 10–20 years PROS: Flexible — draw only what you need. Interest may be tax-deductible if used for home improvement (consult your CPA). Relatively fast to set up (3–6 weeks). CONS: Variable interest rate (currently 8–10% as of 2026). Your home is collateral — if you can't repay, you risk foreclosure. Rates can increase over time. BEST FOR: Homeowners with significant equity (30%+), good credit (700+), and a plan to repay via rental income or refinancing after construction. TYPICAL COSTS: Origination fee ($0–$500), appraisal ($500–$800), annual fee ($50–$100).
Replace your existing mortgage with a new, larger mortgage and pocket the difference. HOW IT WORKS: • You refinance your home for more than you currently owe • The difference comes to you as cash at closing • You use that cash to fund construction • You repay the new, larger mortgage over 15–30 years PROS: Fixed interest rate (currently 6–7.5%). Long repayment term (up to 30 years). Lower monthly payments than a HELOC. CONS: You're resetting your mortgage — if you're 10 years into a 30-year loan, you're extending back to 30 years. Closing costs are 2–5% of the loan amount ($6,000–$20,000 on a $300K refi). You need sufficient equity (usually 20%+ after cash-out). BEST FOR: Homeowners who plan to stay long-term, have significant equity, and want the security of a fixed rate. Especially attractive if current mortgage rates are lower than your existing rate. TYPICAL TIMELINE: 4–8 weeks to close.
The technical side explained in plain English — plan types, PE stamps, structural engineering, and what's required for permits.
Not all plans are created equal. Here's exactly what each level includes and when you need it: LEVEL 1 — CONCEPT PLANS ($0–$500) What's included: Basic floor plan showing room layout, dimensions, and exterior elevations (front/side views). May include a simple 3D rendering. What it's good for: Visualizing the ADU on your property, getting rough contractor estimates, HOA architectural review, early budget planning. What it's NOT good for: Permitting, construction, or financing. A concept plan doesn't have the engineering, MEP, or detail needed to build from. LEVEL 2 — ARCHITECTURAL PLANS ($1,000–$3,000) What's included: Detailed floor plans with dimensions, door/window schedules, roof plan, building sections, exterior elevations, electrical layout, and cabinet layouts. What it's good for: Contractor bidding (much more accurate estimates), construction loan applications, material takeoffs. What it's NOT good for: Building permits. You still need structural engineering, energy calculations, and potentially MEP engineering. LEVEL 3 — PERMIT-READY PLANS ($1,300–$3,500) What's included: Everything in architectural plans PLUS structural engineering (foundation design, framing, lateral/seismic analysis, beam sizing), MEP plans (mechanical, electrical, plumbing layouts), energy compliance documentation, and a PE stamp. What it's good for: Submitting directly to your building department for a permit. This is the complete package. What it's NOT good for: Nothing — this is what you need to get permitted and build.
A PE stamp is the seal of a licensed Professional Engineer. It means a licensed engineer has reviewed and taken responsibility for the structural design. WHAT THE PE STAMP CERTIFIES: • The structural calculations are correct — beams, joists, and connections are sized to carry the required loads • The foundation design is appropriate for the soil conditions and structural loads • The design meets the International Building Code (IBC) and International Residential Code (IRC) • The lateral system (shear walls, hold-downs) can resist wind and seismic forces • The engineer assumes legal liability for the structural design WHY CITIES REQUIRE IT: • Building departments don't have the staff to independently verify every structural calculation • The PE stamp transfers liability from the city to the engineer • PE-stamped plans are reviewed faster because the structural review is already done • Some jurisdictions allow 'over-the-counter' permits for PE-stamped plans WHICH STATES REQUIRE PE STAMPS: Most states require a PE stamp for residential structures that include structural engineering (which ADUs almost always do). The specific requirements vary — some require stamps only for the structural drawings, others for the complete plan set. PE stamps are accepted in all 50 states, but the engineer must be licensed in the state where the project is located. A PE licensed in Texas cannot stamp plans for a California project.
A realistic look at the building phase — what to expect, how to manage it, and how to avoid costly mistakes.
Good preparation prevents 80% of construction problems: • CONFIRM PERMIT IS ISSUED: Never start construction before your permit is approved and issued. Starting without a permit can result in stop-work orders, fines, and having to redo work. • FINALIZE YOUR PLANS: Once the permit is issued, your plans are 'locked.' Any changes after this point require a change order (which costs money and time). Review every detail before submitting. • SELECT YOUR BUILDER: Get at least 3 bids from licensed contractors. Compare not just price but: timeline, experience with ADUs, references, license status, and communication style. • PREPARE YOUR PROPERTY: Move vehicles, clear access paths, mark utility locations (call 811 before digging), protect landscaping you want to keep, and set up a staging area for materials. • NOTIFY NEIGHBORS: Give neighbors a heads-up about construction timelines, working hours, and potential noise. This prevents complaints and keeps relations smooth. • SET UP TEMPORARY FACILITIES: Porta-potty ($150–$300/month), debris bin ($400–$800), water source for construction, temporary power if needed. • ESTABLISH COMMUNICATION: Decide how you'll communicate with your builder (weekly site meetings, text updates, project management software). Set expectations for response time and updates.
Here's what happens physically on your property during construction: WEEKS 1–2 (Site Prep & Foundation): • Excavator arrives — clears the site, digs trenches for foundation and utilities • Concrete forms are set, rebar placed, and foundation poured • You'll see: heavy machinery, dirt, trenches, concrete trucks • Inspections: Foundation pre-pour inspection, then concrete pour WEEKS 3–6 (Framing): • Carpenters frame the floor, walls, and roof • Windows and exterior doors installed • House wrap and sheathing applied • You'll see: the ADU taking shape — from slab to a closed-in structure • Inspection: Framing inspection (before insulation) WEEKS 7–10 (MEP Rough-In): • Plumbers, electricians, and HVAC installers run their systems through the walls and ceiling • This is the 'messy' phase — wires, pipes, and ducts visible everywhere • You'll see: lots of different trades coming and going • Inspections: Rough electrical, rough plumbing, rough mechanical WEEKS 11–13 (Insulation & Drywall): • Insulation installed in walls and ceiling • Drywall hung, taped, and finished • The ADU starts to look like an actual room • You'll see: a dramatic visual transformation from open framing to finished walls WEEKS 14–18 (Finishes): • Flooring installed • Cabinets, countertops, and fixtures installed • Paint and trim • Appliances set • You'll see: the final product coming together WEEKS 19–24 (Final): • Final MEP connections (fixtures, outlets, registers) • Punch list — walk-through to identify any remaining issues • Final inspections • Certificate of Occupancy issued • Clean-up and site restoration
How to find, vet, and manage the right contractor for your ADU project.
Not all general contractors are equipped to build ADUs. Here's how to find the right ones: WHERE TO LOOK: • Ask your city's building department — they see which builders do good work based on inspection results • Check with local ADU prefab manufacturers — they often have certified installer networks • Search your state's contractor license board for active, complaint-free GCs • Ask neighbors who've recently built ADUs — referrals are the most reliable source • Look for builders who specifically advertise ADU experience WHAT TO VERIFY: • License is active and in good standing (check your state's contractor license board website) • No complaints or disciplinary actions on record • General liability insurance (minimum $1M) • Workers' compensation insurance • Bond (required in most states — typically $15,000–$25,000) • At least 3 ADU projects completed in the last 2 years QUESTIONS TO ASK: • 'How many ADUs have you built in the last 12 months?' • 'What's your average timeline from start to Certificate of Occupancy?' • 'Do you handle permits, or do I?' • 'What's your payment schedule?' • 'Who manages the project day-to-day — you or a project manager?' • 'Can I see a current project under construction?' • 'What's your process for change orders?' • 'Do you warranty your work? For how long?'
Getting three bids is standard advice, but comparing them is where most homeowners get tripped up. Here's how to do it right: WHAT A GOOD BID INCLUDES: • Itemized breakdown by trade (site prep, foundation, framing, MEP, finishes) • Specific materials with brands, models, and quantities • Allowance amounts for items not yet selected (e.g., 'Flooring: $4,000 allowance') • Payment schedule tied to milestones • Project timeline with start and completion dates • Inclusions and exclusions clearly listed • Warranty terms RED FLAGS IN BIDS: • Vague line items ('Flooring: TBD') • One-line bids ('ADU construction: $180,000') • No timeline or payment schedule • Bid is 20%+ lower than others — usually means something is excluded • Pressure to sign quickly HOW TO COMPARE: 1. Create a spreadsheet with each bid as a column 2. List every scope item as a row (foundation, framing, electrical, plumbing, HVAC, drywall, flooring, cabinets, fixtures, paint, landscaping) 3. Enter the dollar amount or allowance for each item 4. Note what's included vs. excluded in each bid 5. Add a column for total, timeline, and warranty 6. The lowest bid isn't always the best — weigh completeness, timeline, and communication quality
Real pitfalls that cost homeowners thousands — learn from others' mistakes before you make your own.
1. NOT CHECKING ZONING FIRST: The #1 mistake. Homeowners buy plans or hire designers before confirming their city allows ADUs and understanding the specific requirements. Solution: Check your zoning before spending a dollar on design. 2. ASSUMING 'ADU-FRIENDLY' STATE LAW MEANS YOUR CITY ALLOWS IT: Even in California, local zoning still applies. State law says cities can't ban ADUs — but they can regulate size, setbacks, height, and parking. Solution: Check both state law AND local zoning. 3. IGNORING UTILITY CAPACITY: Your existing electrical panel, water meter, and sewer line may not support a second dwelling unit. Upgrading utilities can add $5,000–$15,000. Solution: Check utility capacity during feasibility, not after permits are submitted. 4. NOT ORDERING A SOIL REPORT: If your soil is expansive clay, sandy, or has a high water table, your foundation design changes. Discovering this during excavation means redesign and delays. Solution: Get a geotechnical report during the design phase. 5. OVERLOOKING HOA RULES: Even if your city allows ADUs, your HOA may prohibit them (unless state law overrides). Solution: Read your CC&Rs before starting.
6. BUILDING TOO SMALL OR TOO LARGE: An ADU that's too small may not meet your needs; one that's too large may exceed zoning limits or cost more than the return justifies. Solution: Think about your intended use (rental, family, office) and match the size to the purpose. 7. POOR WINDOW PLACEMENT: Windows affect natural light, privacy, ventilation, and views. A window facing a neighbor's fence or a wall eliminates value. Solution: Walk the site and think about sightlines from every window before finalizing the plan. 8. IGNORING OUTDOOR SPACE: The ADU isn't just the interior — residents need outdoor space for trash, storage, and relaxation. Solution: Include a small patio, trash enclosure, and landscape buffer in your site plan. 9. NOT PLANNING FOR STORAGE: ADUs are small, and storage is often overlooked. Solution: Include built-in storage, a small shed, or closet space in the design. 10. CHOOSING A PLAN THAT DOESN'T FIT YOUR LOT: A beautiful plan that doesn't respect your setbacks, slope, or utility locations is useless. Solution: Match the plan to your site, not the other way around.
A practical, step-by-step guide to assessing whether your lot can support an ADU — before you spend money.
This is the first and most important step. Here's exactly how to do it: 1. Find your property on your city's zoning map (usually available on the city planning department's website). 2. Identify your zoning designation (e.g., R-1, SF-1, RS-5). Write it down. 3. Search your city's municipal code for 'accessory dwelling unit' or 'secondary dwelling unit' or 'guest house.' 4. Read the requirements for your specific zoning designation. WHAT TO LOOK FOR: • Are ADUs permitted in your zone? (If the code says 'permitted by right' — great. If 'conditional use permit required' — harder but not impossible.) • Minimum lot size requirement (some cities require 5,000+ sqft) • Maximum ADU size (usually 800–1,200 sqft for detached) • Setback requirements (side, rear, front) • Height limits (usually 16 ft for one-story) • Lot coverage maximum (usually 40–60%) • Parking requirement (1–2 spaces, or exempt) • Owner-occupancy requirement • Number of ADUs allowed (1 is standard; some cities allow 2) If you can't find this information online, call your city's planning department. Ask specifically: 'I want to build a detached ADU on my property at [address]. What are the requirements?'
You need to know if your lot is big enough to fit an ADU while meeting setback requirements. WHAT TO MEASURE: • Total lot size (from your property survey or county assessor records) • Current lot coverage: footprint of your house + garage + any other roofed structures • Available backyard space: the area where an ADU could potentially go CALCULATE BUILDABLE AREA: • Maximum lot coverage × lot size = maximum total coverage allowed • Subtract current structure coverage = remaining coverage available for ADU • Example: 6,000 sqft lot × 50% max coverage = 3,000 sqft total. If your house + garage = 2,000 sqft, you have 1,000 sqft available for the ADU footprint. CHECK SETBACKS: • Measure from your property lines to the proposed ADU location • Ensure the ADU fits within the required setbacks • Example: If rear setback is 5 ft and side setback is 4 ft, and your backyard is 30 ft deep × 40 ft wide, your buildable area is (30 - 5) × (40 - 4 - 4) = 25 × 32 = 800 sqft DON'T FORGET ACCESS: • Can construction equipment reach the site? (Narrow side yards or gates may limit access) • Is there a path for utilities from the street to the ADU location? • Will the ADU block existing access to the backyard?
Understanding the financial returns of an ADU — rental income, property value, taxes, and break-even analysis.
Rental rates depend heavily on location, size, and finishes. Here are 2026 national averages: STUDIO (400 sqft): • Low-cost areas (rural, Midwest, South): $700–$1,200/month • Mid-cost metros (Austin, Denver, Atlanta): $1,000–$1,600/month • High-cost areas (SF Bay, LA, NYC, Seattle): $1,500–$2,500/month 1-BEDROOM (550 sqft): • Low-cost: $900–$1,400/month • Mid-cost: $1,200–$2,000/month • High-cost: $1,800–$3,000/month 2-BEDROOM (750 sqft): • Low-cost: $1,100–$1,700/month • Mid-cost: $1,500–$2,400/month • High-cost: $2,200–$3,500/month FACTORS THAT AFFECT RENT: • Private entrance (adds 10–20% to rent vs. shared access) • In-unit laundry (adds $50–$150/month) • Parking (dedicated space adds $50–$200/month) • Pet-friendly policy (adds $25–$75/month pet rent + pet deposit) • Quality of finishes (upgraded kitchen/bath adds 10–15%) • Outdoor space (private patio adds $50–$150/month) WHERE TO FIND LOCAL RENTS: Check Zillow, Apartments.com, Craigslist, and Facebook Marketplace for comparable rentals in your area. Search for 'studio' or '1-bedroom' within 1 mile of your address.
An ADU increases your property value — but how much depends on how it's valued. INCOME APPROACH (most common for ADUs): Appraisers calculate value based on the rental income the ADU generates. • Example: A 1-bedroom ADU renting for $1,800/month = $21,600/year • Using a 5% capitalization rate: $21,600 ÷ 0.05 = $432,000 added value • Using a 6% cap rate: $21,600 ÷ 0.06 = $360,000 added value • The actual value addition depends on local cap rates (typically 4–8%) REPLACEMENT COST APPROACH: Appraisers calculate what it would cost to build the ADU today. • Example: 600 sqft ADU at $250/sqft = $150,000 replacement cost • This often undervalues the ADU in high-rent areas COMPARABLE SALES APPROACH: Appraisers look at similar properties with ADUs that have recently sold. • This is less reliable because ADU comparables are scarce in many markets • Tends to undervalue ADUs because the comparison is imperfect STUDIES AND DATA: • UC Berkeley study: ADUs in California added an average of $100,000–$200,000 in property value • Zillow analysis: Homes with ADUs sold for 35% more than comparable homes without • National Association of Realtors: ADUs are increasingly valued by appraisers as the market matures PRACTICAL REALITY: In most cases, the property value increase exceeds or equals the construction cost. In high-rent areas, the value increase can be 2–3x the construction cost.
If after reading these guides you'd like professional support, here's what we offer — from free concept plans to full permit packages.
Download professionally designed ADU floor plans at no cost. See what fits on your property before spending a dollar on design or permits. Available in studio, 1-bedroom, and 2-bedroom sizes.
A licensed Professional Engineer reviews your specific property address for zoning compliance, setbacks, utility capacity, and buildable area. You get a written feasibility report confirming whether your lot can support an ADU.
Complete plan set: architectural + structural engineering + MEP + energy compliance, all stamped by a licensed Professional Engineer. Ready to submit to your building department for a permit.
Full-service option: PE-stamped plans PLUS site plan, drainage & grading plan, permit coordination, and unlimited revision support. We handle the permit submission process for you.
Engineering plans specifically for converting an existing garage into a livable ADU. Includes structural assessment, MEP design, and PE stamp.
Engineering support during construction — answering builder questions, reviewing structural deviations, and providing additional documentation as needed.
Our engineering team is happy to answer questions about your specific property — no obligation, no pressure.