James Hardie Garage Conversion ADU: The San Francisco Owner’s Guide
Most James Hardie garage conversion projects in San Francisco don’t fail because the framing gives out. They fail because the siding, trim, and flashing details were never matched to the way this city actually weathers a building. We stock and install James Hardie siding, HardieTrim boards, and flashing systems for garage conversion ADUs across San Francisco, with typical siding replacement and repair work running $2,800 to $11,500 depending on exposure, height, and how much of the original install has to come apart. Homeowners usually discover the problem the same way: a soft spot near the bottom edge of a wall, paint that won’t stay stuck, or water showing up inside after a heavy marine-layer week. If you’re reading this because someone told you your James Hardie siding “doesn’t need maintenance” and now it’s failing anyway, you’re in the right place.
Which James Hardie Models This Applies To
Garage conversions in San Francisco typically use one of three James Hardie lines: HardiePlank lap siding, HardiePanel vertical siding, or HardieTrim boards. The compatibility gotcha that trips up most homeowners is this: HardiePlank and HardiePanel are not interchangeable in the same wall assembly without re-flashing the transition. If your original garage conversion used HardiePanel on the street-facing wall and someone patched a section with HardiePlank, the lap joint traps water differently, and it will fail. You can identify what you have by measuring the exposure: HardiePlank comes in 4-inch, 5-inch, 6-inch, and 7-inch exposures, while HardiePanel is a 4×8 or 4×10 sheet with a smooth or stucco texture. The product code is printed on the back of the board. If you can read it, write it down. If you can’t, pull a piece that’s already loose and look at the cut edge. As for OEM versus aftermarket: James Hardie doesn’t sell through third-party “equivalent” brands. What we stock on the truck is genuine James Hardie material ordered through authorized distribution. Aftermarket flashing, however, we buy selectively, because some of the imported metal flashing sold in the Bay Area is thinner than the 26-gauge minimum we want to see on a garage conversion that faces the fog and salt air off the Pacific.
Signs Your James Hardie Garage Conversion ADU Is Failing
- Paint peeling at the bottom 12 inches of the wall. This is usually trapped moisture behind the siding, not paint failure. James Hardie’s fiber cement is dimensionally stable, but if the installer buried the bottom edge below grade or ran the starter strip wrong, water wicks up and pushes the paint off from behind.
- Dark staining or fungal growth at corner trim junctions. HardieTrim boards at outside corners are the first place a garage conversion leaks. The issue is almost always a missing or improperly lapped flashing behind the trim, not the HardieTrim itself.
- Visible gaps between siding courses that widen in dry weather. Fiber cement expands and contracts with moisture. In San Francisco’s damp-winter/dry-summer cycle, boards installed too tight in August will open up by January. The fix is often removing and reinstalling with proper clearance gaps.
- Cracks radiating from nail heads. Hardie recommends nailing no closer than 3/8 inch from the board edge, and never overdriving the fastener. When installers use a framing nailer set too hot, the board fractures at every nail. Those cracks let water in.
- Siding that sounds hollow or moves when you press on it. That means the board was installed over an uneven substrate or with the wrong fasteners. A properly installed HardiePlank wall should feel solid, like a single plane. Movement means the fasteners are already failing or the wall behind it is degrading.
Replacement Cost & What’s Included
For garage conversion ADUs in San Francisco, James Hardie siding and trim replacement typically runs $2,800 to $6,400 for a partial wall or one elevation, and $6,400 to $11,500 for a full re-side including trim, flashing, and paint. What drives the difference: how much of the existing wall assembly has to come apart to do the job right, whether we’re working at scaffolding height or from a ladder, and whether the original installer left proper clearance gaps we can preserve. Every Lodgewick ADU San Francisco quote is a written, line-item price before any work starts. The quote includes material, labor, flashing, disposal, and a written guarantee on the work. We don’t hand you a number and then revise it at the door. The Kingswell Guarantee is a written price first, a defined arrival window, a clean job site, and a free return visit if the work fails within 365 days. That’s the Done Right Promise, and it’s in writing on every project.
DIY or Call Us?
You can safely check a few things yourself: look for gaps between siding courses, check for nail-head cracks, and look at whether the bottom edge of the siding is buried in soil or mulch. What you should not do is pull off a section of HardiePlank to “see what’s behind it.” Fiber cement boards under tension can snap, the cut edges are sharp enough to need a visit to urgent care, and once you remove a board, you’re into the flashing and water-resistive barrier, which means you need to get it back right or the leak you found becomes the leak you caused. We also don’t recommend homeowners work at height on a two-story garage conversion in a city where wind gusts off Twin Peaks can shift a ladder without warning. If you want to know what’s failing and what it’ll cost, call us at (707) 760-0502. We’ll walk the site, measure what’s there, and give you a written number. Russ Delmar quotes a job the same way every time: he walks the wall before he writes the price.
Key Takeaways
- James Hardie siding failures in San Francisco garage conversions are almost always installation-related, not material-related.
- Partial wall repair runs $2,800 to $6,400; a full re-side runs $6,400 to $11,500, including flashing, trim, and paint.
- Genuine James Hardie material only. We stock HardiePlank, HardiePanel, and HardieTrim on the truck, ordered through authorized distribution.
- Every job gets a written price before work starts and a written 365-day guarantee.
- Free estimates: call (707) 760-0502 and a live person answers.
FAQs
James Hardie fiber cement carries a 30-year limited transferable product warranty, and in San Francisco’s mild climate, properly installed siding can last 40 to 50 years. What shortens that lifespan here is installation error: missing flashing, buried bottom edges, and overdriven fasteners. Those failures usually show up in the first 5 to 15 years. Call (707) 760-0502 and we’ll tell you honestly whether your siding is a material problem or an install problem.
Yes, if the damage is localized. A single warped or cracked board can be removed and replaced with a matching Hardie product, as long as the flashing behind it is intact. If the flashing is failing, you have to open the wall assembly, and that’s a larger scope. The honest answer comes from looking at what’s behind the board. Estimates are free.
Most partial wall repairs on a garage conversion take one to two days. A full re-side with trim and paint typically runs three to five working days, depending on weather and whether we find hidden water damage that changes the plan. We give you a defined arrival window before work starts, and we keep the site clean while we’re on it.
We carry HardiePlank lap siding in multiple exposures, HardiePanel sheets, HardieTrim boards, starter strips, and 26-gauge flashing on the truck. If your project needs a specific color or profile we don’t have on hand, we order it through authorized James Hardie distribution and schedule the work when it arrives. Lodgewick ADU San Francisco is an independent service provider and not affiliated with James Hardie. We work with the material because it performs well on San Francisco garage conversions when it’s installed correctly.
Get a Written Estimate for Your James Hardie Garage Conversion ADU
If your siding is failing, don’t guess at the cost and don’t let it sit through another wet winter. Call Lodgewick ADU San Francisco at (707) 760-0502 and we’ll walk the site, identify what’s failing, and put a written price in your hand before any work starts. That’s The Kingswell Way: say the price before the work, show up in the window we give you, leave the place cleaner than we found it, and put the guarantee in writing. We also work with Abodu, Cover, and Dvele garage conversion systems, so if your project involves more than siding, we can talk through the whole scope. Tell us what the space needs to do, and we’ll figure out how to build it right.
Written by Russ Delmar, Owner, Lodgewick ADU San Francisco at Lodgewick ADU San Francisco, serving San Francisco and nearby areas.
