Bolting the sill plate
In an earthquake a house that is not tied down may slide off its foundation. Bolting means fastening the sill plate, the timber resting on the foundation wall, to the concrete with anchors.
Seismic Retrofit and Foundation Bolting in Shoreline
Typical cost in Shoreline
- 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+
Bolting a house to its foundation and bracing the short walls under the floor is the retrofit work Shoreline Foundation Repair does in Shoreline. It is meant to improve how a wood-framed house performs in an earthquake. It does not make a house earthquake-proof, and it does not repair a foundation.
Lake Forest Park and Edmonds are covered as well. Shoreline has 11.7 percent of homes from before 1950 and 65.2 percent from before 1980, so older sills are worth checking.
What a retrofit involves
Bracing cripple walls
Cripple walls, the short stud walls above the foundation, can buckle and collapse sideways in an earthquake, a failure called racking. Sheathing them with plywood is the usual second step after bolting.
Checking the sill and the wall first
Anchors only hold in sound wood and sound concrete. A sill that is soft or a stem wall that is cracked is looked at before anything is fastened to it, which is where crawlspace repair or a crack assessment may come first.
Houses that need a look
Age is a reason to look, not a finding. Whether a particular house is bolted, and how, is checked in the crawlspace: the anchors show as bolt heads and plate washers along the sill, and a cripple wall shows as short studs between sill and floor.
Houses built before 1980 are about 65 percent of Shoreline’s stock, with a median build year of 1969. A newer house can be looked at the same way.
Retrofit standards and building codes
FEMA P-1100, a prestandard for wood light-frame houses, addresses known vulnerabilities. According to its product page the provisions are expected to improve earthquake performance without being intended to prevent damage, and this page keeps to that.
Washington’s 2021 codes have applied since March 15, 2024. Bolt size, spacing and how much wall is braced come from the code and the particular design, so none of those numbers is given here.
Permits and engineers
Whether a bolting and bracing job needs a permit or stamped drawings is for Shoreline’s permit office to say, so ask it before work starts. Registration to practice engineering is a state licensing rule under chapter 18.43 RCW, and it is separate from a permit.
What Shoreline lots and rules add
Shoreline’s critical areas code describes its seismic hazard areas as typically soft or loose saturated soils, such as alluvium or peat, with a shallow water table, and the city maps them from the state’s liquefaction maps for “high” and “moderate to high” risk.
Ask the city whether a given address falls inside a mapped area.
What changes the cost
Wall length and the state of the crawlspace set the cost. The listed range gives a figure to start from, and a look underneath turns it into the written estimate. Five things move it:
- The length of foundation wall to be bolted
- How much cripple wall is there to brace, and its height
- Crawlspace clearance and access
- Sill or framing repairs needed before anchors go in
- Whether the city asks for drawings
Questions and answers
Will a retrofit make my house earthquake-proof?
No. The FEMA P-1100 product page expects improved earthquake performance from the provisions and says they are not intended to prevent damage.
Is bolting the same as foundation repair?
No. Bolting ties the house to the foundation. It does not close cracks, stop settlement or fix drainage, and those have their own pages.
Does my house already have anchors?
The crawlspace answers that. Photos of the sill along the stem wall, taken from the hatch, are enough for a first look.
Fix the sill first if it is soft; crawlspace post and beam repair covers that. Everything else we do is on the Shoreline Foundation Repair home page. Retrofit is aimed at better performance in an earthquake, never at a house that cannot be damaged.
Request a free foundation repair quote
Share the year the house was built, whether a crawlspace or a basement is underneath and whether bolt heads show along the foundation. 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) 532-5454