Bolting the sill plate
The wood sill plate that carries the house walls is fastened to the concrete foundation with anchor bolts and plate washers.
Seismic Retrofit and Foundation Bolting in Renton
Typical cost in Renton
- Bolting and bracing, house about 1,200 sq ft$4,500 – $10,500+
- Bolting and bracing, house about 2,000 sq ft$7,500 – $17,500+
- Bolting and bracing, house about 3,000 sq ft$11,000 – $26,000+
On this page: Renton Foundation Repair’s work in bolting older crawlspace houses down and bracing their cripple walls, the houses that come into question, and what such work cannot promise.
We work in Renton, Kent and Tukwila. Renton has about 39 percent of its homes built before 1980. Bolting concerns wood-frame houses on a crawlspace and stem wall.
Bolting and bracing
Bracing cripple walls
Between foundation and first floor stands the cripple wall, a short run of studs. Strong shaking can make it buckle and collapse, which engineers call racking, and plywood sheathing nailed on the studs is one way to brace it.
Connectors
Connectors are the small steel plates and straps in this work. They join the floor framing to the sill and foundation, and the house and its plan decide how many go in and where.
What a retrofit does
A house can slide off its foundation in a quake and cripple walls can buckle. Bolting and bracing aim to make that less likely. FEMA P-1100, a method for finding and fixing known weaknesses in wood-frame homes, states that its provisions are expected to improve performance but are not intended to prevent damage.
That is the honest limit. A retrofitted house can still be damaged, and we never describe one as earthquake-proof.
Houses that need a look
The construction concerned is a wood-frame house on a crawlspace, with a sill plate resting on a stem wall. Renton’s pre-1980 share is about 39 percent.
Whether a particular sill is bolted, and with what, is found by looking in the crawlspace.
Retrofit standards and building codes
The reference for engineers is FEMA P-1100, covering wood-frame one- and two-family houses. Washington’s 2021 state codes became effective on March 15, 2024. Ask the Renton permit center which code edition applies at your address.
Permits and engineers
Ask the Renton permit center whether bolting or bracing needs a permit or an engineer at your address. A contractor’s registration with the state is a licensing rule and not a permit rule.
If the foundation itself is cracked or has settled, the foundation repair comes before the bolting. See foundation settlement and piering and foundation crack repair.
What Renton lots and rules add
Renton’s critical areas code groups steep slopes, landslide, erosion and seismic hazards, and coal mine hazards, as geologically hazardous areas. If the crawlspace sits on a slope or the foundation is cracked, tell the permit center when you ask about a retrofit.
The state publishes earthquake ground-response information, including liquefaction susceptibility, on the DNR Geologic Information Portal, and it is a general guide. Peat, which is mapped on its own because it is not liquefiable, can still deform in shaking and need site-specific analysis.
Questions and answers
Does bolting make my house earthquake-proof?
No. It is meant to reduce the chance of the house sliding off its foundation, and a retrofitted house can still be damaged.
Does my house have anchor bolts already?
You find out by looking in the crawlspace at the sill plate along the foundation wall. We can check.
Does a retrofit need a permit?
Ask the Renton permit center for your address. A contractor’s state registration is a licensing rule, not a permit.
Bolting comes late in a sequence: the wood has to be sound and the foundation steady. Decayed posts or sills are crawlspace post and beam repair, and the full list of work is on the Renton Foundation Repair home page.
Request a free foundation repair quote
Is there a crawlspace, and can you see the sill plate and any bolts? We'll get back to you soon with an estimate or any questions we have. Estimates are free and there's no obligation.
Call (425) 276-6261