Concrete Foundations in Seattle
Seattle ConcreteCONTRACTORS
(206) 566-0528
Footings, stem walls and slab-on-grade foundations for additions, garages, backyard cottages, sheds and decks, poured to the engineer’s plan.
- Built to stamped plans and inspections
- Footings sized for the soil you actually have
- Drainage and vapor barrier planned in
Get a foundation quote
Tell us about the project. We’ll call or email to talk it through.
What to know about concrete foundations in Seattle
Foundation work is concrete where the drawings and the inspector set the rules. For an addition, a detached garage, a backyard cottage (DADU) or a large shed, the plans say how deep the footings go, how much steel goes in, and where anchor bolts and hold-downs sit. Our job is to dig, form, place steel and pour exactly to that plan, and to flag soil or water problems before the concrete goes in.
Additions
Footings and stem walls that tie into an existing house foundation.
Garages and carports
Slab-on-grade with thickened edges, or footings and stem walls.
Backyard cottages (DADUs)
Foundations and slabs for detached accessory units.
Sheds and studios
Smaller slabs and footings sized for the structure.
Deck and porch footings
Pier footings and pads poured to plan.
Foundation repair
Underpinning and structural repair are engineer-led; we can talk through what’s involved.
Options to talk through
| Type | Good for | Keep in mind |
|---|---|---|
| Slab-on-grade | Garages, sheds, some ADUs | Needs a solid base, vapor barrier and thickened edges |
| Continuous footing + stem wall | Additions and wood-frame houses with a crawlspace | Two-stage pour; matches many older Seattle homes |
| Pier footings | Decks, porches and posts | Sized and spaced per plan |
How Seattle’s ground and weather affect concrete foundations
Soil and slope
Seattle soils change from dense glacial till to soft fill. On slopes or soft ground, an engineer may call for deeper footings or a geotechnical report.
Seismic details
Hold-downs, anchor bolts and reinforcement follow the plan; they matter in our earthquake zone.
Water
Footing drains and a vapor barrier under slabs help keep crawlspaces and floors dry.
Inspections
SDCI inspects footings and steel before the pour on permitted work. We schedule around that.
Critical areas
Steep slopes and landslide-prone areas mapped as ECAs bring extra review.
Access
Tight lots and back-yard ADUs may need a pump to get concrete to the forms.
Planning a new foundation in Seattle?
Call to talk it through, or send a few details and photos.
How the job runs
- Review plansGo over drawings, soils notes and schedule.
- Excavate and formDig to depth, set forms and place steel.
- InspectionCity inspection of footings and reinforcement before the pour.
- Pour and stripPour, cure, strip forms and backfill.
What concrete foundations typically cost in the Seattle area
Ballpark numbers help you plan a budget before anyone visits. Use them as a starting point, not a promise.
| Foundation work | Typical range |
|---|---|
| Slab-on-grade (base, vapor barrier, rebar, pour) | $6–$14 per sq ft |
| Continuous footing | $40–$90 per linear ft |
| Stem wall + footing | $80–$150 per linear ft |
| Foundation repair or underpinning | $5,000–$20,000+ per project |
Typical market ranges, not a quote from Seattle Concrete Contractors. These are ranges other Seattle-area concrete contractors publish for this work (Seattle Concrete (seattleconcrete.com) service pages, checked November 2026). Your price depends on size, access, removal, base work, finish and permits. We give a written quote after we understand the job.
What affects the price
These are the things that move a quote most, in roughly the order they matter.
Plans and soil
Engineered footings on poor soil cost more.
Depth and height
Deeper footings and taller stem walls use more concrete and steel.
Access
Pumping into back yards adds cost.
Excavation
Rock, roots and haul-off of soil add time.
Inspections
Scheduling inspections can affect crew time.
Drainage
Footing drains and waterproofing are often separate items.
What a good written quote should include
Whoever you hire, ask for these in writing. They’re what separate a slab that lasts from one that cracks in two winters.
Scope and size
The area, thickness and shape, so you can compare quotes on the same job.
Base and drainage
How deep the excavation goes, how much gravel, and where water goes.
Reinforcement and joints
Rebar or mesh, dowels into existing concrete, and joint spacing.
Finish and sealing
The finish, whether it’s sealed, and what upkeep to expect.
Removal and cleanup
Demolition, haul-away and site restoration.
Permits and schedule
Which permits apply, who pulls them, and cure time before use.
Concrete Foundations: common questions
Do you work from engineered plans?
Yes. Foundations are built to the approved plans and inspected. If you don’t have plans yet, your designer or engineer comes first.
Do I need a permit for a foundation in Seattle?
Foundations for additions, garages, ADUs and most structures are part of the building permit through SDCI.
How long does a foundation take?
Excavation, forming and steel take most of the time; inspection timing and cure time set the rest. Small jobs can be a week or two.
What’s the right foundation for Seattle soil?
It depends on the soil and the structure, and the engineer decides. Soft or wet ground may call for deeper footings or a soils report.
Do you do underpinning or foundation repair?
Structural repair is engineer-led and site specific. Call us to talk through what’s involved before you commit to anything.
Can a new foundation tie into my old one?
Yes, with dowels and details specified by the engineer, which is standard for additions.
Other areas we serve
Concrete Foundations planning notes, permits and local conditions for each city we cover.
Foundations in BellevuePhotos are illustrative, not completed projects of ours.
Concrete Slabs
Retaining Walls
Concrete Steps & Stairs
Concrete Repair & LevelingTell us about your project
A few photos and rough measurements are enough to start. If you’re not sure what the job needs, describe the problem and we’ll talk it through.
Call (206) 566-0528 or use the quote form at the top of this page.
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Seattle Concrete Contractors | (206) 566-0528 | Seattle, WA