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# Joist and Sill Plate: The sill plate is the bottom horizontal piece of…

**Category:** Construction & Remodeling · **Complexity:** Technical · **Also known as:** floor joist, rim joist, mudsill

## Definition

The sill plate is the bottom horizontal piece of wood (typically pressure-treated 2x6 or 2x8) bolted to the foundation, on top of which the floor joists rest. Joists are the parallel horizontal members that span between sill plates and walls to support the subfloor and finished flooring above.

## Common Questions

### Why do sill plates rot in PNW homes?

Crawl space humidity, ground moisture wicking through unsealed concrete, and foundation grading issues all expose the sill plate to constant moisture. Untreated or older sill plates rot before the joists do.

### Can a rotted sill plate be repaired?

Yes, but it's invasive — the home must be temporarily lifted with cribbing, the rotted material cut out, and new pressure-treated lumber installed and bolted. A licensed contractor with foundation experience is essential.

## Real-World Example

You'd see this when a homeowner in Vancouver, WA notices uneven floors near an exterior wall — CRM Services inspects the crawl space and finds rotted sill plate sections requiring partial replacement before encapsulation.

## Why It Matters

Sill plate and joist work is core scope on CRM Services' foundation and crawl space remediation projects across the PNW.

## Related Terms

- [Framing](https://www.crmsvc.com/glossary/framing.md): Framing is the skeleton of a building — the network of wooden studs, joists, beams, and headers that gives a structure its shape and supports everything above it.
- [Subfloor](https://www.crmsvc.com/glossary/subfloor.md): The subfloor is the structural layer of flooring nailed or screwed directly to the floor joists.
- [Crawl Space Encapsulation](https://www.crmsvc.com/glossary/crawl-space-encapsulation.md): Crawl space encapsulation is the process of sealing a home's crawl space with a heavy-duty vapor barrier across the floor and walls, conditioning the air, and addressing insulation and ventilation.
- [Load-Bearing Wall](https://www.crmsvc.com/glossary/load-bearing-wall.md): A load-bearing wall is a wall that supports the weight of the structure above it and transfers that load down to the foundation.

## Related Services

- [services dry rot repair](https://www.crmsvc.com/services/dry-rot-repair.md)
- [services](https://www.crmsvc.com/services.md)

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*CRM Services, LLC — Licensed, bonded & insured home remodeling and repair contractor in Vancouver, WA (WA license CC CRMSESL844MK). Serving Clark County and SW Washington within 50 miles. 5.0★ from 41+ Google reviews, A+ BBB. Call (503) 898-0276, email quotes@crmsvc.com, or request a free estimate at https://www.crmsvc.com/#contact*