Design-Build & Structural Engineering in Sammamish, WA
ECD takes projects across the Sammamish Plateau from our Bellevue office, about 12 miles and 25 minutes away. Sammamish homeowners most often hire us to open up the closed main floors of 1980s and 1990s two-story houses, build detached ADUs on larger lots and engineer foundations on the steep slopes above Lake Sammamish.
How does Sammamish review remodels and ADUs?
The City of Sammamish issues building permits through MyBuildingPermit.com. Sammamish incorporated from unincorporated King County, so many houses were permitted by the county before the city existed, and those records are held by King County. Structural interior remodels go through building review; additions and ADUs add zoning review and, on many lots, stormwater review because the plateau drains to Lake Sammamish and salmon streams.
Two reviews come up often here. Steep slope and landslide hazard areas cover much of the hillside between the plateau and East Lake Sammamish Parkway, and projects there usually need a geotechnical report. Stream buffers on creeks used by Lake Sammamish kokanee, such as Ebright Creek and Laughing Jacobs Creek, limit where new structures can go on nearby lots.
Sammamish housing stock and what it means for your remodel
Most Sammamish houses were built from the 1980s through the 2000s in planned subdivisions: two-story houses with a formal living room, a family room off the kitchen, a two-story entry and tall vaulted ceilings. Framing is typically engineered I-joist floors and roof trusses over a crawlspace, sometimes with a daylight basement on sloped lots.
That construction shapes what a remodel can do. I-joists cannot be notched or drilled outside their manufacturer's limits, so moving plumbing through the floor needs planning. Two-story walls at entries and great rooms often carry wind loads and rely on specific framing, so removing or shortening them needs engineering. The good news is that bearing lines in these houses are usually regular and easy to trace, and opening the kitchen, dining and family rooms into one space is a very achievable project.
Site constraints common in Sammamish
- Steep slopes on the west side of the plateau above East Lake Sammamish Parkway.
- Salmon stream buffers along creeks draining to Lake Sammamish.
- HOA architectural review in most subdivisions, often required before permit submission.
- Septic systems on some older or larger lots, which affect whether an ADU can be added without a sewer connection.
- Lake shorelines on Lake Sammamish, Pine Lake and Beaver Lake.
Projects completed in Sammamish
PROJECT · SAMMAMISH PLATEAUA detached ADU set into a sloped backyardA 640-square-foot cottage on a stepped foundation with a sewer connection routed along the side yard.Sammamish neighborhoods we serve
Beaver Lake, East Lake Sammamish, Inglewood, Klahanie, Pine Lake, Sahalee, Sammamish Plateau, Trossachs.
Sammamish questions
Remodeling in Sammamish: common questions
Can I open up the main floor of my 1990s Sammamish house?
In most cases, yes. The walls separating kitchen, dining and family rooms in these houses often carry the upper floor, so they need a beam, but bearing lines are regular and beams can usually be set flush in the I-joist floor above. The engineer checks the I-joist layout, point loads and footing capacity under new posts before design.
Will my Sammamish HOA need to approve a DADU?
Very likely. Most Sammamish subdivisions have covenants requiring architectural review for detached structures, exterior materials and colors, and some limit outbuildings. State law restricts how cities regulate ADUs but does not cancel private covenants. We review your HOA documents during feasibility and prepare the submission the committee needs.
Can I build an ADU on a Sammamish lot with a septic system?
Sometimes. An ADU adds wastewater flow, so the septic system must have capacity for the added bedrooms or be expanded, with approval from Public Health – Seattle & King County. If sewer is available nearby, connecting may be required or simpler. We check sewer availability and septic records for your lot first.
Does a steep slope on my lot stop an addition?
Not necessarily, but it changes the process. The city will usually require a geotechnical report and may set buffers from the top of the slope. Foundations are often deeper or use piers. Some additions move to the uphill side of the house or become second stories instead. We assess slope constraints before you invest in design.
Free estimate · Bellevue office
Talk to the engineer before you commit to a plan
A site visit, a scope conversation and a written budget range, at no cost.