Design & Construction

From Plans to Permits to Build

This is where your ADU project goes from spreadsheet to reality. Design and construction is the longest, most expensive, and most variable phase of the process. The decisions you make here — build method, floor plan, finishes, contractor management — determine whether your project hits the numbers you modeled in RISE or blows through them.

Build Method: Three Paths

Path 1: Stick-Built (Traditional Construction)

What it is: Conventional on-site construction. A crew frames walls, installs systems, and finishes the unit piece by piece on your property.

Best for: Custom designs, complex sites, garage conversions, and projects where the ADU needs to match the main dwelling's architectural style.

Pros:

• Maximum design flexibility — any layout, any size, any configuration
• Easier to navigate plan check because the construction method is familiar to inspectors
• Can work around site constraints (odd-shaped lots, slopes, existing trees, tight access)
• Local contractors are readily available

Cons:

• Longest construction timeline (3–6 months for a conversion, 4–8 months for ground-up)
• Most vulnerable to weather delays, labor shortages, and material cost fluctuations
• Quality depends heavily on your specific contractor and crew

Cost range: $150–$350/sq ft depending on market, scope, and finishes

Path 2: Prefab / Modular

What it is: The ADU is manufactured in a factory and delivered to the site as one or more modules. Site work (foundation, utility connections) is done in advance, and the unit is craned or trucked into place.

Best for: Ground-up detached ADUs on lots with adequate access for delivery, investors who want speed and cost predictability.

Pros:

• Faster construction timeline (factory build can happen while site work is underway)
• More predictable pricing — factory controls costs better than field construction
• Consistent quality — factory conditions eliminate weather variables
• Some manufacturers handle design, permitting, and installation as a package

Cons:

• Delivery access is critical — you need a clear path for a crane or flatbed truck to reach the site
• Less design flexibility — you're choosing from the manufacturer's options
• Foundation and site work are additional costs not included in the manufacturer's base price
• Some jurisdictions treat modular differently than site-built for permitting purposes
• Lender financing may vary — confirm with your lender that they'll finance a prefab ADU

The "all-in" reality: Prefab manufacturers often advertise prices like "$99,000 for a 500 sq ft ADU." The actual all-in cost after foundation, site prep, utility hookups, permits, delivery, crane, and finishing work is typically 40–60% higher than the advertised base price. Budget accordingly.

Cost range: $120–$280/sq ft all-in (including site work, foundation, delivery, and hookups)

Path 3: Conversion (Garage, Shed, Interior)

What it is: Transforming an existing structure into a permitted dwelling unit. The scope ranges from minor interior work (JADU) to significant structural modification (full garage conversion with new foundation work).

Best for: Investors seeking the lowest cost and fastest timeline. Properties with existing structures that are structurally sound and reasonably sized.

Pros:

• Lowest cost path to a completed ADU
• Fastest timeline — the shell already exists
• Least site disruption — you're working within an existing footprint
• May qualify for simplified permitting in some jurisdictions

Cons:

• Limited by the existing structure's size, layout, and condition
• May uncover hidden issues (foundation problems, water damage, inadequate electrical) once demolition begins
• Ceiling height, natural light, and layout constraints can limit the finished product's appeal

Cost range: $60–$200/sq ft depending on condition of existing structure and scope of work

Designing Your ADU

Floor Plan Principles

Whether you're designing a 400 sq ft studio or a 1,200 sq ft two-bedroom, these principles maximize livability and rental value:

Open layouts: In small units, every square foot matters. Open kitchen-living areas feel larger and are more functional than chopped-up rooms. Use furniture placement, not walls, to define zones.

Functional kitchens: Even a studio ADU needs a real kitchen — not a kitchenette with a hot plate. Full-size refrigerator, four-burner range or cooktop, adequate counter space, and a sink. This is what separates a rentable unit from a glorified hotel room.

Natural light: Maximize windows. Small units feel small when they're dark. Building codes require minimum window area for habitable rooms (typically 8% of floor area), but go beyond the minimum. Tenants will pay more for a bright unit.

Storage: The number one complaint from tenants in small units is lack of storage. Build in closets, kitchen pantry space, and consider creative solutions like lofted storage or built-in shelving.

Separate entrance: The ADU should have its own dedicated entrance that doesn't require walking through shared space or past the main dwelling's windows. Privacy for both the ADU tenant and the main home occupants is essential.

Outdoor space: Even a small patio or deck significantly increases an ADU's appeal and rent potential. A 6x8 patio with a fence costs very little and adds meaningful value.

Design for Your Target Tenant

Long-term renters: Prioritize storage, in-unit laundry (or hookups), and a functional kitchen. Neutral finishes that are durable and easy to maintain.

Short-term rental / Airbnb: Prioritize aesthetics, outdoor space, and a "wow factor." Higher-end finishes, good lighting, and a design that photographs well. Consider furnishing the unit.

Specific demographics: If your market's ADU demand is driven by graduate students, single professionals, or senior adults, design accordingly. Senior tenants may value ground-floor living and wider doorways. Students may prioritize desk space and high-speed internet infrastructure.

Finish Level and Budget

Don't over-build. The finish level should match the market, not your personal taste.

Standard / rental grade: Laminate or LVP flooring, painted cabinets, laminate countertops, standard fixtures. This is appropriate for most long-term rental ADUs. Cost-effective and durable.

Mid-range: LVP or tile flooring, soft-close shaker cabinets, quartz countertops, upgraded fixtures and lighting. Appropriate for higher-rent markets or short-term rental units where aesthetics affect nightly rates.

High-end: Custom tile, premium cabinetry, stone countertops, designer fixtures. Rarely justified for an ADU unless you're in a luxury market and the rent premium covers the additional cost. Run the numbers before you upgrade — a $15,000 kitchen upgrade needs to generate at least $150–$200/month in additional rent to justify itself over a 10-year hold.

The Permitting Process

Pre-Application (Optional but Recommended)

Many cities offer pre-application meetings or over-the-counter consultations where you can:

• Confirm ADU feasibility for your specific lot
• Discuss development standards and design requirements
• Get informal feedback on your preliminary plans
• Identify potential issues before you invest in full architectural plans

Cost: usually free or a small fee ($100–$500). Time: 1–4 weeks to schedule.

Plan Submission

Once your architect has completed the construction drawings, you submit to the city's building department for plan check. The submission typically includes:

• Architectural plans (floor plan, elevations, sections, site plan)
• Structural engineering (foundation, framing, lateral design)
• Mechanical plans (HVAC layout)
• Electrical plans
• Plumbing plans
• Title 24 energy compliance (California) or equivalent energy code documentation
• Site plan showing setbacks, lot coverage, utility connections
• Application forms and fees

Plan Check Review

The building department reviews your plans for code compliance. Timelines vary dramatically:

• Fast markets: 2–4 weeks (over-the-counter in some jurisdictions for ADUs)
• Average markets: 4–8 weeks
• Slow markets: 8–16 weeks (Los Angeles, San Francisco, and other high-volume cities)

You will likely receive "plan check comments" — a list of required corrections or additional information. Your architect addresses these and resubmits. Each round of corrections adds 2–4 weeks. Minimize rounds by having an experienced local architect who knows what the city wants to see.

Permit Issuance

Once plans are approved and all fees are paid, the permit is issued. You can now begin construction. The permit is typically valid for 12–24 months (varies by jurisdiction). If construction hasn't started or isn't progressing, the permit can expire.

Inspections During Construction

The city will require inspections at key milestones:

• Foundation (before pouring concrete)
• Framing (before closing walls)
• Rough mechanical, electrical, and plumbing (before insulation and drywall)
• Insulation and energy compliance
• Final inspection

Schedule inspections in advance. Failed inspections cost time — your crew may not be able to work until the correction is made and re-inspected. A good contractor anticipates inspection requirements and has the work ready.

Certificate of Occupancy

After the final inspection passes, the city issues a certificate of occupancy (CO). This is the document that says the unit is legal, safe, and habitable. You need the CO to:

• Rent the unit legally
• Get an appraisal based on the completed ADU
• Refinance the property
• Sell the property with the ADU represented as a legal unit

Construction Management

The Draw Schedule

If you're using a construction loan (which you should be for most ADU projects), your lender releases funds in "draws" as construction progresses. A typical draw schedule:

How it works:

1. Contractor completes a milestone
2. You (or your contractor) submit a draw request to the lender
3. The lender sends an inspector to verify the work is complete
4. The lender releases the draw amount
5. You pay the contractor

This process protects you (you only pay for completed work) and the lender (funds are disbursed proportional to progress). Revolution Realty Capital's draw process is designed to be fast — our inspections are typically scheduled within days of the draw request, not weeks.

Budget Management

Track every dollar. Maintain a running budget that compares actual costs to your original estimate for every line item. Update it after every draw, every material purchase, and every change order.

The contingency is not a bonus. Your 15–20% contingency exists to absorb surprises — not to be spent on upgrades. Common surprises that eat contingency:

• Foundation issues discovered after demolition
• Electrical panel upgrade required by the inspector
• Plumbing rerouting due to unexpected conditions
• Additional fire separation requirements
• Material price increases between bid and purchase

If you spend your contingency on granite countertops instead of holding it for unknowns, you'll be scrambling when a real surprise hits.

Change Order Management

Change orders — modifications to the original scope of work — are where budgets go to die. Manage them aggressively:

• Get every change order in writing with a specific cost before approving
• Understand the difference between an owner-requested change (your choice) and a field condition change (necessary)
• Track the cumulative impact of change orders on your total budget and timeline
• If change orders are pushing your total cost above what RISE says is profitable, stop and reassess before continuing

Timeline Management

Construction timelines slip. It's not a question of if, but how much. Build buffer into your RISE model and manage actively:

• Weekly check-ins with your contractor (on-site, not by phone)
• Ask for a detailed schedule with milestones and target dates at the start
• Track progress against that schedule weekly
• Address delays immediately — don't wait and hope they'll catch up
• Every week of delay adds carrying costs (interest, taxes, insurance, utilities) that eat your profit

The ADU Construction Timeline (Realistic Estimates)

Add the permitting phase to get your full timeline from project start to CO. These ranges assume no major delays. In your RISE model, use the upper end of the range plus one month of buffer.