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Tremron Home Additions & ADU: The San Francisco Owner’s Guide
A Tremron home addition or ADU in San Francisco typically runs $53,100 to $153,400 installed, depending on foundation work, square footage, and whether we’re tying into existing utilities or trenching new lines. We plan, permit, and build Tremron-compatible additions and accessory dwelling units start to finish, and we stock the common framing, flashing, and connection materials on the truck so a site visit doesn’t stall on a missing strap or hanger. Most owners call us after realizing their existing structure is pulling away at the connection point, or after a city inspector flags the original build for non-compliant shear transfer.
This page covers what fails first on San Francisco additions and ADUs, what a rebuild or repair actually costs, and what we check before we ever hand you a written price. If you have a Tremron structure that is leaning, separating, or showing water at the tie-in, you’re in the right place.
Which Tremron Models This Applies To
Tremron manufactures segmental retaining wall and paver systems more than traditional wood-framed additions, so when a San Francisco homeowner asks us about a “Tremron addition,” they’re usually describing an attached room, sunroom, or ADU built on a Tremron block foundation or retaining system. The failure point is almost never the block itself. It’s the connection between the Tremron wall system and the wood framing above it, or the drainage behind the wall that was never installed correctly in the first place.
How to identify what you have: Look for the manufacturer stamp on the back face of any exposed block, or check the original permit drawings if you have them. Tremron’s Dublin and San Rafael product lines are common in Bay Area builds. The block dimensions will tell us what we’re working with, but the critical spec is the wall height and the soil behind it. A 4-foot retaining wall holding back saturated clay behaves completely differently than a 2-foot decorative course. The compatibility gotcha most people miss: Tremron block is not a structural foundation for a habitable addition unless the original engineer specified it and the county approved it. We regularly see freestanding Tremron walls that were later “converted” into ADU foundations with no permit and no engineering. That is the first thing we check.
On the aftermarket side, there is no meaningful “OEM vs aftermarket” decision for the block itself. Tremron block is Tremron block. The decisions that matter are the grout, the rebar schedule, the drainage aggregate, and the connection hardware, and those are spec’d by an engineer, not a catalog.
Styles & brands we work with
Signs Your Tremron Home Addition or ADU Is Failing
- Separation at the tie-in. The wall or addition pulls away from the main house by a quarter inch or more. This is almost always a shear connection failure: the original build used toe-nails instead of approved straps and hold-downs. In San Francisco’s wind and seismic conditions, that connection is the first thing to go.
- Water staining at the base of the wall. Fog-driven moisture moves through older balloon-frame walls in the Outer Sunset and similar neighborhoods, and if the Tremron wall has no weep holes or crushed-rock drainage behind it, hydrostatic pressure builds and pushes water through the joint. You’ll see efflorescence, dark staining, or actual seepage.
- Diagonal cracks at the corners. Cracks that run at a 45-degree angle from a window or door corner usually mean differential settlement. The Tremron foundation section may be moving at a different rate than the original slab, especially where the soil was over-excavated and backfilled without compaction.
- Sticking doors or windows inside the addition. This is a deflection problem. The framing above the Tremron wall is racking because the connection points are rotating. In San Francisco’s soft-story and hillside conditions, that rotation only gets worse through a wet winter.
- Rot at the sill plate. Untreated lumber sitting directly on block wicks moisture out of the masonry. We find this on nearly every older Tremron-based addition in the Richmond and Sunset districts. The fix requires lifting or shoring the structure, replacing the sill, and installing a capillary break.
See the difference
Before
After
Before
After
Before
AfterReplacement Cost & What’s Included
Here is the straight number for San Francisco:
- Sill plate replacement and re-anchoring: $5,310 – $14,160
- Shear connection retrofit with new hold-downs and straps: $8,260 – $21,240
- Drainage correction behind a Tremron wall (excavate, add aggregate and drain, re-compact): $4,130 – $12,980
- Full tear-out and rebuild of a failed Tremron addition: $53,100 – $153,400
- New ADU construction on engineered Tremron foundation: $106,200 – $259,600
What moves the number is access, soil conditions, and whether we are working around your family or doing a full vacate. Every price we give in San Francisco is written before work begins, with the parts, labor, and permitting broken out line by line. No numbers move at the door. If the engineer requires a change during construction, the change order is written, signed, and priced before we pick up a tool. That is The Garrison Standard, and it is non-negotiable.
Every completed job carries the 365-Day Done Right Promise. If the connection fails, the drainage clogs, or the framing shifts inside that year, we come back and correct it at no charge. You get that in writing before we start, and a signed copy in your hand when we close out.
DIY or Call Us?
You can safely check a few things yourself: look for daylight between the addition and the main house, check for water staining after a rain, and note whether doors that swung fine last year are sticking now. Write down what you see, take photos, and keep a log. That helps our site visit.
What you should not do is start jacking, shoring, or drilling into a Tremron wall that may be under load from a hillside or a second story sitting on top of it. A retaining wall can fail suddenly when the soil behind it is saturated, and a misjudged cut can put thousands of pounds of earth and framing into motion. This is genuinely dangerous work, not a weekend project. If you are seeing separation, cracking, or movement, call (831) 610-5598 and let Curtis Lane walk the site with you. The estimate is free, and you’ll get a straight answer on scope before you spend a dime.
FAQs
A properly engineered Tremron-based addition with correct drainage and connection hardware should last 50 years or more on the structural side, and we’ve seen well-built examples in the Sunset holding fine after 40. What kills them early, every time, is water. In San Francisco’s fog belt, walls without capillary breaks and drainage rot from the bottom up within 10 to 15 years. Call (831) 610-5598 for an inspection if your addition is over a decade old and you’ve never checked the sill.
Yes, in most cases. Sill replacement, shear retrofits, and drainage correction are routine repairs we do without tearing the whole structure down. A rebuild is only necessary when the framing above has racked so far that the wall is no longer plumb or the foundation itself has settled beyond what an engineer will certify. We’ll tell you which one you’re looking at after a site visit, not a guess over the phone.
A sill replacement or shear retrofit typically runs 5 to 10 working days. A full addition rebuild or new ADU runs 3 to 8 months depending on permitting and scope. We give you a written timeline with the written price, and we hold to it. Call (831) 610-5598 for a schedule estimate on your specific job.
We stock the common connection hardware, sill plates, anchors, drainage pipe, and aggregate on the truck, so most repair site visits can start the same day. Tremron block itself is ordered from the local San Rafael or Dublin yard as needed. We also work with KraftMaid, Cambria, and Silestone for interior finish materials on ADU projects, so the whole scope stays under one written contract.
Written by Curtis Lane, Owner, Bradford Remodeling Co – San Francisco, CA at Bradford Remodeling Co San Francisco, serving San Francisco and nearby areas.
