Plant Prefab Garage Conversion ADU Nationwide

Plant Prefab Garage Conversion ADU: The San Francisco Owner’s Guide

If you own a Plant Prefab garage conversion ADU in San Francisco and a component has failed, this page tells you exactly what’s involved in getting it fixed. We stock Plant Prefab-compatible garage conversion ADU parts and install them for $220 to $780 on average, depending on the specific part and your model. Most owners discover something’s wrong through a symptom they can feel or hear: a door that no longer seals tight against the fog and wind off Ocean Beach, a window that’s suddenly impossible to open, or a floor transition that’s started to pull away from the prefab wall panel because moisture has crept in where it shouldn’t. The good news: these are known failure points on garage conversions, and they’re almost always repairable without replacing the entire module.

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Key Takeaways:

• We stock Plant Prefab-compatible replacement parts for garage conversion ADUs and install them on the same visit in most San Francisco neighborhoods.
• Typical installed cost runs $220 to $780, with a written price before we lift a tool.
• We are an independent service provider, not affiliated with Plant Prefab, but we work with their panels and component sizing daily.
• Moisture intrusion at panel joints is the single most common failure we see in San Francisco’s marine climate, and it’s fixable without gutting the structure.

Which Plant Prefab Models This Applies To

Plant Prefab builds garage conversion ADUs using their standard panelized wall system, which means the parts that fail tend to be the interfaces: the threshold plates, the sill gaskets, the corner trim that bridges the existing garage slab and the new prefab wall. Any Plant Prefab model built on a garage slab foundation in San Francisco shares these components. The specific part you need comes down to which generation your panels carry. Older Plant Prefab units, roughly 2017 to 2021, used a slightly narrower sill channel (1⅝ inches) than current production, which runs 2 inches. If you order a current sill gasket for an older panel, it won’t seat correctly and you’ll see daylight under the wall plate. Check the stamped metal tag on the bottom track of any exterior wall panel: it will list the panel series and a build date. That tag is the fastest way we match you to the right part without guesswork. When it comes to OEM versus aftermarket, we carry both. Plant Prefab’s OEM seals and trim are fine products, but they’re priced at a premium and sometimes backordered by several weeks. For non-structural items like gaskets, sweep seals, and transition strips, the aftermarket equivalents we source from Bay Area suppliers often exceed the OEM spec for UV resistance, which matters more in San Francisco than most people expect given how much intense sun the west-facing Sunset and Richmond districts actually get.

Signs Your Plant Prefab Garage Conversion ADU Is Failing

• Drafts coming under the exterior wall. This usually means the sill gasket has compressed or deteriorated. In San Francisco, the constant moisture cycle from fog and rain leaches the plasticizer out of rubber components faster than the manufacturer’s dry-climate testing would predict.
• Visible gap between the wall panel and the garage slab. Soil settling under the original garage foundation is common in Noe Valley and Glen Park, where older slabs sit on expansive clay. The gap itself isn’t structural failure, but it lets moisture and pests in if the seal isn’t replaced.
• Corner trim pulling away or warping. Plant Prefab uses aluminum trim at panel corners, and the thermal expansion difference between the metal trim and the wood-fiber panel is significant. In San Francisco’s wide daily temperature swings, the trim fasteners loosen over time. You’ll notice it as a slight bow that wasn’t there a year ago.
• The entry door dragging or failing to latch. Garage conversions sit on slabs that were never intended to support a finished living space, and differential settling is real. The door frame itself is fine; the threshold plate underneath has shifted by a quarter inch or less. This is a threshold replacement, not a door replacement, and it’s a two-hour fix.
• Condensation or mustiness near the floor line on the garage-door side of the unit. The original garage door opening is the trickiest part of any garage conversion to seal properly. The bottom track of the conversion wall is the most common leak point. We see this in Bernal Heights and the Mission regularly, where older garages have no vapor barrier under the slab.

Replacement Cost & What’s Included

In San Francisco, most Plant Prefab garage conversion ADU part replacements run between $220 and $780 installed. A sill gasket replacement on one wall section typically lands around $220 to $340 including the part. Corner trim with new fasteners and sealant runs $350 to $520 depending on how many corners need work. A full threshold plate replacement on the entry door is the higher end, usually $600 to $780, because it requires lifting the door frame slightly and re-shimming it square. What drives the range is access and the condition of what’s underneath once we open things up. If we find the concrete spalling where the old anchor bolts sit, that adds surface prep time. You get a written price before any work starts, no exceptions, and that price doesn’t change unless you ask us to add scope. Every replacement carries the 365-Day Done Right Promise: if the part or our installation fails within one full calendar year, we come back and make it right at no charge. No haggling, no inspection fee, no “well, it depends on when it started.”

DIY or Call Us?

There are things worth checking yourself and things worth leaving alone. You can safely inspect your sill gaskets, corner trim, and threshold plates with a flashlight and a straightedge. Look for compression, gaps, or loose fasteners. That’s useful information to have before you call, and it helps us quote more accurately over the phone. What you shouldn’t attempt is pulling the threshold plate or corner trim yourself. Those components are fastened through the panel into the slab, and on older Plant Prefab conversions in San Francisco, the anchor points often carry a small amount of shear load. Removing them incorrectly can shift the panel enough to crack interior drywall or damage the waterproofing membrane. That turns a $300 job into a $3,000 job. If you’ve confirmed something is wrong and you want a straight answer on what it’ll cost, call us at (831) 272-7212. You’ll speak with a live person, not a queue, and we’ll tell you honestly whether it’s urgent or can wait.