Rotted Sill Plate and Rim Joist Behind Siding — Repair
A screwdriver sinks into the wood just above the foundation, behind the siding or under the deck. That is the sill and rim, the part the whole wall sits on, and it gets replaced in sections.
A rotted sill plate and rim joist behind the siding is repaired from outside: JMB Builders opens the siding at grade, supports the floor and wall above, cuts out the rot in sections, and replaces it with treated sill and new rim, then flashes it and puts the siding back. Common under deck ledgers and beside patios. Twin Cities and north metro, priced per project from photos, with an engineer when the damage is long.
- Priced per project, by the section
- House supported while rot is cut out
- Treated sill, new rim, flashed and re-sided
- Engineer on long runs or failed framing
- Licensed MN contractor BC809005
The sill plate sits on the foundation and the rim joist sits on the sill; the floor joists and the wall above land on both. When water gets to them for years they rot, and the usual sources are the same on house after house: a deck ledger bolted on without flashing, a patio or grade sloped toward the wall, siding run down to the dirt, a missing kickout above, or a leaking hose bib.
The repair is done from outside, a section at a time. The siding and sheathing come off at the bottom of the wall. The floor and wall above are supported with shoring so nothing drops. The rotted rim and sill are cut out in lengths short enough to keep the house carried, replaced with treated sill on a sill gasket and new rim, and fastened to the foundation and the joists. Rotted joist ends are sistered. Then the wall is wrapped, flashed, and re-sided.
When the rot runs a long way, joists are badly damaged, or the wall above has dropped, an engineer looks at it and writes the repair, and structural work usually needs a building permit that JMB pulls. At a deck, the ledger comes off, and the deck either goes back with proper flashing and spacers or gets free-standing posts so it no longer hangs on the house.
What you supply
- Photos of the soft area outside and, if you can, from the basement looking at the rim
- Photos of the deck ledger, patio or grade next to it
- Leftover siding if you have it, or the siding type and color
- Access in the basement to the joist ends behind the repair
What JMB supplies
- Siding and sheathing removal at the bottom of the wall
- Temporary shoring to carry the floor and wall while rot is cut out
- Treated sill plate on a sill gasket, new rim joist, and anchors to the foundation
- Sistered joist ends where they rotted
- New sheathing, house wrap and flashing at the foundation and any ledger
- Deck ledger reflashed and reset, or the deck made free-standing
- Siding back on or matched, permit when needed, and photos in your job folder
How it is priced: per project
Quoted in writing from your photos within one business day. What moves the number:
- Length of rim and sill that is rotted once the siding is open
- Joist ends, studs or wall sheathing rotted along with it
- Whether a deck ledger has to come off and go back
- Siding type and whether it can be reused or must be matched
- Basement finish that has to be opened inside
- Engineer's letter and permit when the run is long or framing has dropped
Probe the wood with a screwdriver at a few points and send photos of where it goes soft and where it turns solid. That sets the likely length.
How long it takes
One short section under a door or ledger: one to two days. A long run along a wall with a deck ledger reset: several days.
How your project works
- 1
Send photos, get a written quote
Send three photos of the space and a sentence about what you want. You get a clear, itemized quote within one business day. We only come out to measure first when the job needs a tape measure — no pressure, no games.
- 2
Pick materials, or bring your own
We help you choose profiles and materials that fit the house and the budget, or match your existing millwork exactly — or you buy the door or trim yourself and we install it. Everything is confirmed before the crew is scheduled.
- 3
Clean, precise installation
The crew shows up on time, protects floors and furniture, and installs with tight joints and consistent reveals. Photos of the finished work go in your job folder.
- 4
Walkthrough and invoice
We walk the finished work with you. If anything is not right, we fix it before we call the job done. Then one invoice, paid by check or direct deposit — no card fees, no payment links.
Rotted Sill Plate and Rim Joist Behind Siding — Repair: questions, answered
How do you repair a rotted sill plate and rim joist behind siding?
The siding and sheathing come off at the bottom of the wall, the floor and wall above are shored, and the rot is cut out in short sections. Each section is replaced with a treated sill and new rim, anchored to the foundation and fastened to the joists, before the next section is opened. Then the wall is wrapped, flashed and re-sided.
How do you fix a rotted rim joist under a deck ledger?
The deck is supported and the ledger comes off. The rotted rim is cut out and replaced, the joist ends behind it are checked and sistered where needed, and the wall is flashed. The ledger goes back with flashing over it and spacers so water drains, or the deck gets its own posts and no longer hangs on the house.
What causes a rim joist to rot?
Water sitting against it for years. The usual sources are an unflashed deck ledger, a patio or soil sloped toward the house, siding run down to the ground, a missing kickout flashing above, or a leaking outdoor faucet. The rot starts where the water lands and spreads along the rim.
Can the sill plate be replaced without lifting the house?
Yes, in sections. Shoring carries the floor and wall a few feet at a time while the old sill is cut out and the new one slid in and anchored. The house is not jacked up as a whole; it is supported in place so the drywall and windows above stay put.
Do I need an engineer for a rotted rim joist?
Not for a short section where the joists and wall above are sound. When the rot runs a long way, several joist ends are gone, or the wall or floor has dropped, an engineer looks at it and writes the repair. Structural repair like this usually needs a building permit, and JMB pulls it.
How do I know if the rim joist behind my siding is rotted?
Push a screwdriver into the siding and trim just above the foundation. Soft wood, a sagging bottom course, stains or mushrooms in the basement at the rim, or a floor that dips at the outside wall are all signs. From the basement, look at the rim above the foundation for dark, crumbly wood.
Recent JMB work, from our job log
59 installs recorded across 30 Twin Cities communities since Dec 2025. Window and door installs for homeowners and for the builders and dealers we sub for. Counts come straight from our job log; no customer names.
Get a written quote for this job
Three photos and a sentence is enough. You hear back within one business day. Or text the photos to 763-204-2099.
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Read morePage reviewed September 26, 2026 · JMB Builders LLC, MN license BC809005 · All exterior trim pages
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