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Sterling Home Additions & ADU: The San Francisco Owner’s Guide
Bradford Remodeling Co San Francisco designs and builds Sterling-compatible home additions and ADUs throughout San Francisco, with full-project pricing that typically runs $53,100 – $153,400 for a home addition and $106,200 – $259,600 for a detached ADU. We’re an independent contractor, not a Sterling dealer, which means we match the workload to your existing structure without steering you toward parts you don’t need. Most owners call us after a failed first attempt with another crew: a foundation that settled wrong, a roofline that doesn’t tie in cleanly, or an ADU shell that leaks at the wall-to-roof junction within the first rainy season.
When a home addition fails, the signs are rarely subtle. You’ll see cracking at the seam where the addition meets the original house, a floor that slopes toward the new foundation line, or moisture staining at the transition flashing. In San Francisco’s fog belt, particularly the Outer Sunset and Richmond districts, a poorly detailed transition between old and new framing pulls moisture into the wall cavity year-round. That’s not a cosmetic problem. That’s a structural one, and it’s the most common reason we’re called in to correct another contractor’s work.
Which Sterling Models This Applies To
Sterling’s home addition and ADU line spans three general classes: bump-out additions, full-room extensions, and freestanding accessory dwelling units. The compatibility question is less about a model number and more about how the original structure was framed and what the foundation will carry. San Francisco’s older housing stock, much of it balloon-framed with perimeter foundations, behaves differently under load than a modern platform-framed house. A bump-out on a 1920s Outer Sunset home needs a different transition detail than the same addition on a 1990s build in Noe Valley.
For OEM versus aftermarket material decisions, we treat the addition as a system, not a part swap. The sheathing, flashing, fasteners, and tie-downs all have to be compatible with the existing wall assembly. Sterling’s proprietary transition flashing is well-made, but we routinely substitute or supplement with GAF or James Hardie products where the existing roof or siding system demands a matched profile. That’s the difference between a written spec and guesswork. We document the material brands in the scope before work starts, so you know exactly what’s going on your house.
One compatibility catch worth knowing: San Francisco’s wind exposure and seismic requirements mean your addition’s hold-down hardware and shear wall specifications have to be calculated for your specific site, not pulled from a national template. A Sterling addition design that works in Sacramento may need different hardware in the Sunset or Twin Peaks. We run those numbers before the permit drawings go in, not after the inspector flags the rough-in.
Styles & brands we work with
Signs Your Sterling Home Additions & ADU Is Failing
- Cracking at the old-to-new wall junction. This indicates differential settlement or inadequate tie-in between the addition’s framing and the original structure. The two sections move at different rates, and the finish surface splits along the seam.
- Floor slope or bounce near the addition’s foundation line. A foundation that wasn’t sized for the soil conditions or that lacked proper drainage will settle unevenly. In San Francisco’s sandy western neighborhoods, undersized footings shift within the first two years.
- Water staining or soft drywall at the roof-to-wall transition. This is a flashing failure. Fog-driven moisture from the west side of the city works into any gap at the transition and sits inside the wall cavity.
- Doors or windows in the addition that stick or won’t latch. When the structural framing settles or racks, the openings go out of square. This is a structural signal, not a hardware adjustment.
- Persistent musty smell in the new space, even in dry weather. Moisture trapped in the wall cavity from improper vapor barrier or flashing detail will produce odor long before you see staining on the finished surface.
See the difference
Before
After
Before
After
Before
AfterReplacement Cost & What’s Included
In San Francisco, a full home addition runs $53,100 – $153,400, and an ADU build ranges from $106,200 to $259,600 depending on size, foundation work, utility runs, and finish level. The range is driven by square footage, site access, and what we find when we open the walls on the existing structure. A bump-out with a simple foundation runs at the lower end. A full ADU with a new service panel, trenching for sewer, and hardscape disruption runs at the upper end.
Every estimate is a written line-item price before we start. That includes demolition, dump fees, materials, rough-in, finish work, and the permit package. No numbers move at the door. The 365-Day Done Right Promise covers the completed work for a full year: if anything we built fails inside that window, we return and correct it at no charge. That’s not a verbal assurance. It’s a signed guarantee in your hand at close-out, next to the documented scope of work.
| Scope | San Francisco Installed Range |
|---|---|
| Home Addition (bump-out to full room) | $53,100 – $153,400 |
| ADU Construction (detached) | $106,200 – $259,600 |
| Garage Conversion | $35,400 – $94,400 |
| Kitchen Remodel (for reference) | $16,520 – $53,100 |
Call (831) 610-5598 and we’ll walk the site, run the numbers, and hand you a written price you can hold up against any other bid.
DIY or Call Us?
What you can safely check yourself: look for cracking at the transition seam, test the floor for slope with a level, and check the attic space above the addition for daylight coming through the flashing. These observations help us diagnose before we arrive. What you should not do is attempt to jack a settled foundation, pull apart wall framing, or re-flash a roof transition. Structural repair under load is dangerous. A compromised shear wall or improperly shored foundation can shift suddenly, and roof work on a steep San Francisco pitch with fog-slick surfaces is not a weekend project.
If you’re seeing movement, water, or cracking at the addition’s tie-in points, get a trained set of eyes on it. Curtis Lane has worked San Francisco’s older housing stock for over two decades, including gut-and-rebuild projects in the Outer Sunset where fog-driven moisture through balloon-frame walls taught us exactly how fast a bad transition detail becomes a structural problem. Call (831) 610-5598 and we’ll come out, assess the failure, and give you a straight number to fix it right.
FAQs
A properly built addition in San Francisco should last 50+ years structurally, but the failure point is almost always the transition between old and new construction, not the addition itself. In fog-exposed neighborhoods, that transition needs re-inspection every 5 to 7 years. If you’re seeing separation or moisture at the seam within the first two years, the original work didn’t meet the site conditions. Call (831) 610-5598 and we’ll correct it under a written guarantee.
Most failures can be repaired through targeted foundation work, re-flashing, and selective reframing without demolishing the entire addition. The decision comes down to whether the structural issue is localized or systemic. If the foundation was undersized across the whole footprint, repair costs can approach replacement on a small bump-out. We’ll give you both numbers in writing before you commit to either path.
A targeted correction, such as re-flashing a transition or repairing a settling corner, typically takes 1 to 3 weeks. A full foundation correction under an existing addition can run 4 to 8 weeks depending on access and permit timing in San Francisco. You’ll get a written timeline in the scope document, and we hold to it. Call (831) 610-5598 for a date-specific schedule.
We maintain relationships with local San Francisco suppliers for framing lumber, engineered beams, flashing, and the documented brand products we install, including James Hardie, GAF, Therma-Tru, and Kohler. That means most standard materials are on the truck or available same-week. For specialty items like custom-milled transition flashing or engineered hold-down hardware matched to your seismic zone, we order ahead and stage the material before the crew starts demo.
Straight number, real scope, no surprises at close-out.
If you’ve got a Sterling home addition or ADU that’s cracking, leaking, or moving, don’t wait for the next rainy season to test the flashing. Call Curtis Lane and the Bradford Remodeling Co San Francisco crew at (831) 610-5598 for a free estimate. We also work with KraftMaid, Cambria, and Silestone products for kitchen and bath work tied to the addition. Every job gets a written price before we start, and every finished project carries the 365-Day Done Right Promise in writing.
Written by Curtis Lane, Owner, Bradford Remodeling Co – San Francisco, CA at Bradford Remodeling Co San Francisco, serving San Francisco and nearby areas.
