Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
CWS Home Additions & ADU: The San Francisco Owner’s Guide
A CWS home addition or ADU project in San Francisco typically runs $53,100 to $153,400 depending on square footage, foundation work, and whether you’re building up or out. We install and build CWS-compatible home additions and ADU projects, and most San Francisco owners discover they need this work when their existing space stops functioning: a garage that’s too damp for storage, a backyard that’s dead weight, or a growing family that’s outgrown a two-bedroom layout. The fix is rarely a patch. It’s a properly framed, permitted addition that adds real square footage and holds value.
You’ll hear a lot of contractors toss around square-footage ballparks that sound too good to be true. They usually are. In San Francisco, the real costs come from three places: seismic requirements, foundation work on sloping lots, and the permitting process itself. We’ll walk you through what actually drives the number before you sign anything.
Key Takeaways:
- Home additions in San Francisco run $53,100 – $153,400; ADU construction runs $106,200 – $259,600.
- The biggest cost drivers are foundation type, lot slope, and seismic detailing – not cabinet finishes.
- Every CWS addition or ADU project gets a written price before work starts and the 365-Day Done Right Promise in writing at close-out.
- We’re an independent San Francisco contractor, not affiliated with CWS – but we build additions and ADUs that meet or exceed the structural and seismic standards CWS owners expect.
Which CWS Projects This Applies To
CWS home additions and ADU projects aren’t a single product line. They’re site-built structures, which means the “compatibility” question is really about your lot, your existing foundation, and your local code requirements. If you own a CWS home in San Francisco, the addition or ADU has to tie into the existing structure correctly – wall alignment, roof pitch, foundation depth, and seismic connections all have to line up with what’s already there.
The first thing we check on any San Francisco CWS home is the foundation type. Older CWS homes in the Outer Sunset, the Richmond, and parts of the Excelsior were built on perimeter concrete or post-and-pier foundations. Newer ones often have slab-on-grade. That single detail changes the structural approach, the permit path, and the price by tens of thousands of dollars. The second thing we check is lot slope. San Francisco topography means a “simple” backyard ADU can turn into a retaining wall and drainage project fast.
When it comes to OEM versus aftermarket thinking – this applies more clearly to fixtures and finishes than framing. For structural work, there’s no such thing as an aftermarket floor joist. You spec lumber and steel to code. But for the parts of an addition that are replaceable – windows, doors, cabinets, counters, plumbing fixtures – you do have choices. We work with documented brands: KraftMaid and Wellborn cabinetry, Cambria and Silestone surfaces, Kohler and Moen fixtures, Therma-Tru doors, James Hardie siding. These aren’t guesses. They’re name-brand products with manufacturer specs and warranties that back up our own guarantee. Bradford Remodeling Co San Francisco is an independent service provider, not affiliated with CWS. That means we’re free to spec the right materials for the job instead of whichever brand a corporate office prefers.
Styles & brands we work with
Signs Your CWS Property Is Ready for an Addition or ADU
- Your family has outgrown the footprint, not the neighborhood. You’re not looking to move; you’re looking for another bedroom, a home office, or a second bathroom. The underlying cause is straightforward: the house didn’t grow, but the household did. An addition solves that without uprooting your kids from their school or your commute from your routine.
- The garage is too damp or too narrow for anything but junk. In the fog belt, garages that were never insulated or properly sealed collect moisture. You can convert that space into a legal ADU with proper waterproofing, insulation, and egress. The underlying cause of the dampness is usually a lack of vapor barrier and poor drainage, not some unfixable curse of the lot.
- Your backyard is dead weight. A flat or gently sloped San Francisco yard can hold a detached ADU from 400 to 800 square feet without killing the whole outdoor space. If the yard isn’t being used for anything except mowing and regret, that’s square footage waiting to earn rent or house a relative.
- You’re working from a kitchen or bedroom that was never designed for it. San Francisco homes built before remote work existed have rooms sized for sleeping and cooking, not video calls and spreadsheets. When the dining table becomes a permanent desk, the underlying problem is a missing room, not a missing filing cabinet.
- Rental income is the missing line in your budget. A legal, permitted ADU in San Francisco can rent for enough to offset a mortgage or fund a remodel. If you’ve run the numbers and the missing piece is a rentable unit, that’s a structural answer to an income question.
See the difference
Before
After
Before
After
Before
AfterReplacement Cost & What’s Included
Here’s the straight number range for San Francisco, and what sits inside it:
- Home Addition: $53,100 – $153,400
- ADU Construction: $106,200 – $259,600
- Garage Conversion: $35,400 – $94,400
- Kitchen Remodel (attached to an addition): $16,520 – $53,100
- Bathroom Remodel (attached to an addition): $10,620 – $33,040
What drives the range: foundation type (slab is cheaper than post-and-pier retrofit), lot slope (a flat lot is cheaper than one that needs retaining walls), seismic requirements (San Francisco is in Seismic Design Category D, which means more hold-downs, more strapping, more engineering), and finish level. A basic ADU with stock cabinets and laminate counters lands on the low end. A detached unit with Cambria or Silestone surfaces, custom KraftMaid cabinetry, and Kohler fixtures lands higher.
What’s included in our price: the written scope, the permit drawings, the structural engineering, all labor, all materials, debris removal, and the 365-Day Done Right Promise in writing at close-out. No change orders that weren’t discussed before the work began. No door-price adjustments. Curtis Lane reviews every scope document before it goes to the homeowner.
DIY or Call Us?
You can measure your lot, check your zoning, and sketch what you want. That’s useful homework. You can also pull your property’s permit history from the San Francisco Department of Building Inspection website to see what’s already on record. Those are safe, smart steps that save time.
What you should not do is swing a sledgehammer at a load-bearing wall, dig a foundation trench without a soils report, or run electrical or plumbing without a permit. In San Francisco, unpermitted work on an addition or ADU will bite you at resale, during an insurance claim, or when a neighbor files a complaint. Foundation and seismic work is also genuinely dangerous: a collapsed trench or a compromised bearing wall can kill. We carry the liability, the engineering, and the relationships with DBI and the planning department so you don’t have to learn those lessons the hard way.
Call us at (831) 610-5598 for a free estimate. We’ll walk the lot, talk through what’s realistic for your budget, and put the number in writing.
FAQs
Most home additions take 4 to 8 months from permit submittal to final inspection; ADUs typically run 6 to 10 months. The variable that slows everything is permit review time at DBI and the planning department, which we manage but cannot control. Call (831) 610-5598 and we’ll give you a realistic timeline for your specific scope.
Yes, in most San Francisco neighborhoods a garage conversion is legal if you meet the city’s ADU ordinance requirements, including ceiling height, egress, and seismic upgrades. Garage conversions run $35,400 – $94,400 and often move faster than new construction because the shell already exists. We’ll tell you during the first walk whether your garage qualifies.
No. We write the scope and the price before any work begins, and the only way a change order appears is if you add scope mid-project or a hidden condition emerges that we flag and get your approval on first. That’s the whole point of a written price: no surprises at close-out.
Yes. We pull all required permits, schedule the inspections, and carry the project through final approval. The written warranty you receive at close-out covers the work for a full year through our 365-Day Done Right Promise. Straight number, real scope, no surprises at close-out.
Call (831) 610-5598 for a free estimate on your CWS home addition or ADU in San Francisco.
Written by Curtis Lane, Owner, Bradford Remodeling Co – San Francisco, CA at Bradford Remodeling Co San Francisco, serving San Francisco and nearby areas.
