A step-by-step guide to building an ADU in San Francisco, from feasibility and design through permits, foundation, framing, MEP rough-in and final inspection.
Building an ADU in San Francisco runs in twelve stages: feasibility, design, structural engineering, utility planning, permit review, site preparation, foundation, framing, MEP rough-in, insulation and drywall, finishes, and final inspection. The stages cannot be reordered, and the permit stage is the one most often underestimated.
Look at the lot, the access, the existing structure and the utility supply. Decide whether a garage conversion, an attached or a detached ADU makes sense here. This costs nothing and saves the most.
An architect produces a layout and permit drawings that work with the existing house and the constraints of the lot.
Anything carrying load gets engineered — foundation, framing, and any connection to or alteration of the existing structure.
Establish where water, sewer, gas and electrical will come from and whether the existing service has spare capacity. This is the item most often left too late.
Drawings go in. Review takes as long as it takes. Nothing should be ordered or scheduled on the assumption it will be quick.
Clearing, protection, access for materials and machinery. On a constrained San Francisco lot this can mean hand-digging and carrying spoil through the property.
Excavation, forms, reinforcement, inspection of the reinforcement, then the pour.
Floor, walls and roof. The structure goes up quickly compared with everything around it, which is why it feels like progress after a long paper stage.
All three run through open framing, then are inspected before anything is covered.
Insulation goes in after the rough-in passes. Drywall hung, taped and finished.
Kitchen, bathroom, flooring, millwork, fixtures and paint — the stage where the finish level chosen at the start shows up in the cost.
Final sign-off, snagging worked through, and the unit handed over.
Ask who is responsible for design, who is responsible for engineering, and who is responsible for construction — and get it in writing. Ask how changes are priced once work begins. Ask what happens if the permit takes longer than expected. Ask to see a written estimate with each trade as its own line rather than one lump sum.
What drives ADU cost in San Francisco and the San Francisco ADU permit process. To talk about a specific property, see ADU construction with Leafair.
A site visit and a feasibility check. Before drawings are paid for, someone should look at the lot, the access, the existing structure and the utilities, because those four things determine whether an ADU is straightforward or difficult on your property.
Design and engineering run for months before construction can start, permit review adds more, and construction depends on the type of ADU. Treat the permit stage as a real schedule item rather than a formality.
An ADU requires permit drawings, so yes in practice. Leafair is a licensed general contractor and refers clients to architects and structural engineers it works with rather than offering design services it is not qualified to provide.
Leafair will walk the site, talk through what is realistic, and give you a written estimate priced line by line. Estimates are free.
