Sammamish zoning and building permits: what you can build on your lot in 2026

Short answer: on most Sammamish lots you can build one house plus up to two accessory dwelling units, as long as the house fits inside setbacks that get deeper as the house gets bigger, a floor area cap of half the lot, a hardscape cap that counts the driveway, a 35 foot height limit and a tree retention rule. Slopes, streams and lake frontage can take a big bite out of that.

For how I work here, see my Sammamish architect page. The figures below come from the city’s development standards pages and handouts, the Sammamish Development Code (Title 21 of the Sammamish Municipal Code, SMC) and the ordinances that amended it. They are as of September 2026, so confirm with the city before you rely on any number.

Sammamish’s residential zones and how to find yours

The residential zones are R-1, R-4, R-6, R-8, R-12 and R-18. The number is the maximum density in homes per acre, so R-4 allows four homes per acre and R-1 one. Since January 1, 2025, three middle housing overlays also sit on top of R-1 through R-8.

To find your zone, open the Property Tool on the city’s Maps and GIS page. It layers zoning with slopes, landslide and erosion hazards, streams, wetlands and shoreline designations. Its zoning layer is labelled 2016, as is the PDF zoning map on the same page, so confirm the current zone with a written Project Guidance request. The city says it answers those within one week.

The core numbers, zone by zone

These are the house standards in R-1, R-4, R-6 and R-8, from the residential site planning table in SMC 21.04.030.C as adopted in December 2024 and the city’s current R-4 and R-6 pages.

FAR is floor area ratio. Front yards along arterial streets are 30 feet in every zone. In R-8, side yards may drop to 5 feet where the neighbor is zoned R-8, R-12 or R-18.

Setbacks that grow with the house

Know this rule before you choose a floor plan. In R-4 and R-6 the setbacks are set by the size of the building, in three tiers:

Sources: SMC 21.04.030.C; City of Sammamish handouts No. 120 and No. 130 (March 2025) and the R-4 and R-6 development standards pages. Arterial front yards are 30 feet in every tier. Properties in shoreline jurisdiction must also meet SMC Title 25.

The handouts add that where the front yard is 15 feet, a garage needs 20. The “average” yards work by area: where part of the house sits inside the average line, an equal or larger area elsewhere must sit behind it.

Here is what the tiers do on an 80 foot wide R-4 lot. Under 2,500 square feet, 5 foot side yards leave a band 70 feet wide (80 minus 10). From 2,500 to 4,000, the two 10 foot average side yards leave 60 feet. Over 4,000, the 12 foot averages leave 56 feet, the front yard moves from 20 to 25 feet and the rear average from 20 to 25. Ask the city early how it measures the building’s size for the tier, for example whether an attached garage is included, because that answer can move you across a line.

Floor area, the upper floor cap and height

Floor area ratio. A house is limited to 50 percent FAR in R-1 through R-8. Per the city’s FAR page, floor area counts the garage and any lower floor whose exterior wall is more than three feet above ground. ADUs, basements with less than three feet of exposed wall, and open decks, porches and carports do not count. Going over 50 percent needs a zoning variance.

Watch the lot area you divide by. Under SMC 21.04.030 as the city printed it in 2024, steep slopes, wetlands, streams and their buffers are not credited toward floor area. On a 15,000 square foot lot with 3,000 square feet of stream buffer, the cap works from 12,000, so 6,000 square feet of house instead of 7,500.

The 3,000 square foot cap. The December 2024 update added a 3,000 square foot building footprint maximum per building. Ordinance O2026-594 (passed February 3, 2026, effective February 14) rewrote that line as a maximum floor area for upper level floors of 3,000 square feet per building, with a one-time, cumulative 300 square foot expansion allowed per building for any upper level floor. An upper level floor is any floor more than five feet above the main entry’s finished floor. The city’s R-4 and R-6 pages still describe it as a building footprint limit, so confirm how it will be applied to your plans.

Height. Buildings may be 35 feet, and side walls 24 feet. Ordinance O2025-583 (effective June 14, 2025) changed how height is measured. Where grade changes less than 6 feet from the front wall to the back wall, height runs from the average existing grade at the midpoints of the walls. Where it changes 6 feet or more, the house is split into segments at least 15 feet long, each measured from its own average grade. A director’s interpretation noticed July 30, 2026 (COD2026-00382) treats existing grade as the grade when a complete building permit application goes in, including grading the city has approved.

Hardscape: the driveway counts

The city counts as hardscape anything covered by buildings, driveways, walks, decks, gravel or pavers. The caps are 30 percent in R-1, 40 percent in R-4, 50 percent in R-6 and 75 percent in R-8. ADUs built under the ADU rules are exempt from hardscape and FAR on a lot with a single-family house.

On a 12,000 square foot R-4 lot the numbers look like this: 6,000 square feet of floor area (12,000 x 0.50) but only 4,800 square feet of hardscape (12,000 x 0.40), and that 4,800 has to cover the roof footprint, the driveway, the patio and every walk. A 100 foot driveway 12 feet wide uses 1,200 square feet, a quarter of it. Public Works stormwater rules apply on top of these limits.

Tree retention

A significant tree is a conifer 8 inches in diameter or larger, or a deciduous tree 12 inches or larger. A new primary residence in R-1, R-4 or R-6 needs a land use permit or approval before any significant tree comes down, and the city’s tree page says that on sites where development is proposed or anticipated, no trees may be removed until a construction permit is issued.

• R-4 and R-6: keep at least 35 percent of the significant trees outside critical areas and their buffers.
• R-1: keep at least 50 percent.
• Any zone: erosion hazard areas and the Pine Lake and Beaver Lake drainage sub-basins must keep 50 percent.
• During construction: protection fencing at least 4 feet high goes 5 feet beyond the drip line of each protected tree before any land disturbance.

These percentages are from SMC 21.03.060 as the city printed it in 2024; I found no later change, but confirm. On a wooded lot I bring the arborist in before the first sketch, because the trees you must keep often fix where the house can go. My guide to building around trees covers the design side.

Steep slopes and other critical areas

Of the critical areas (wetlands, streams, habitat, flood areas and geologic hazards), landslide rules matter most on sloped lots. A landslide hazard area includes slopes of 40 percent or steeper with 10 feet or more of vertical relief, among other conditions. A project on or within 50 feet of one needs a 50 foot buffer from the top and toe of the slope. Since January 1, 2025 (Ordinance O2024-571) the city may reduce or remove that buffer if a critical areas report, including a geotechnical report, shows the house, the neighbors and the slope stay protected.

Most clearing and grading may only happen between May 1 and September 30, so a late start can push site work to the next spring.

Lake Sammamish, Pine Lake and Beaver Lake lots

Shoreline lots also fall under the Sammamish Shoreline Master Program (SMC Title 25). The city’s shoreline page sets the headline number: a 50 foot shoreline setback from the ordinary high water mark (OHWM) on Lake Sammamish, and 45 feet on Beaver Lake and Pine Lake, with very limited development allowed inside it. On Lake Sammamish the city puts the OHWM between 28.0 and 28.2 feet (NGVD29), though a project may need a professional to set it. How a house on the water gets its shoreline sign-off is covered in my guide to shoreline exemptions for single-family homes.

Middle housing and ADUs

ADUs. A lot with a detached house may have up to two ADUs, attached, detached or one of each. A detached ADU is capped at 1,000 square feet; an attached one can be up to 50 percent of the house or 1,000 square feet, whichever is larger. A stand-alone detached ADU needs 5 foot side and rear setbacks and may be 24 feet tall. More in my Sammamish ADU guide.

Middle housing. The overlays adopted in December 2024, in effect since January 1, 2025, are MHO-1 on R-1, MHO-2 on R-4 and MHO-3 on R-6 and R-8. The city says middle housing is not mandatory. In the adopted text, R-4 lots may carry the greater of three units per lot or 12 per acre, and R-6 and R-8 lots the greater of three per lot or 18 per acre, rising to four per lot with an affordable unit, when the existing home is kept, or within a quarter-mile walk of an existing or planned transit stop. FAR rises by 0.15 per added unit, from 0.65 for two units to 1.25 for six. The state law behind this is covered in my HB 1110 guide.

The affordable housing fee and impact fees

Sammamish’s Inclusionary Affordable Housing Program (SMC 21.10) applies to new homes. Ordinance O2026-597 (passed August 18, 2026, effective August 29) raised the exemption from 1,500 to 1,750 square feet, exempted additions, expansions and involuntary rebuilds, and limited the fee to floor area above 1,750. The exemptions apply retroactively to January 1, 2025.

The city’s 2026 development fee schedule sets the in-lieu fee at $34.45 per square foot. Floor area here means finished living space measured from the exterior walls; garages and unfinished basements are left out. A new house with 4,000 square feet of it would pay (4,000 minus 1,750) x $34.45 = $77,512.50. For a teardown, the amendment deleted the old credit for the original house’s floor area, and the exemption for new or reconstructed homes stops at 1,750 square feet, so ask the city how your rebuild will be treated.

Since July 1, 2026, parks and transportation impact fees are charged per square foot up to 3,500 square feet: parks 3,500 x $3.13 = $10,955.00, transportation 3,500 x $7.44 = $26,040.00 (the city’s impact fee page says $26,043.91). A new house of 3,500 square feet or more pays about $37,000 for the two. Additions are exempt, and a replacement house applied for within 12 months of the demolition permit pays only for added floor area (SMC 21.06.045). The 2026 schedule lists school impact fees per new house of $10,914.75 in Lake Washington, $19,690.27 in Snoqualmie Valley and $0 in Issaquah.

The building department, the portal and timelines

Sammamish’s Building Division is part of Community Development at City Hall, 801 228th Avenue SE. Every application, tree removal permits included, goes in online through MyBuildingPermit.com. The Permit Center (425 295 0531) takes walk-in questions on Monday, Wednesday and Friday and books virtual appointments with plans examiners, engineers and planners.

For the building code, the city’s adopted codes page lists the 2021 Washington State codes, with local amendments in SMC Title 16. The State Building Code Council says the 2024 codes take effect May 3, 2027, so submission date decides the edition.

Timelines. The only review times I found the city publishing are for small steps: one week for a Project Guidance answer, and two business days to screen a tree removal application, then five to review it. As of September 2026 the Building and Project Guidance pages also warn that staff transitions may temporarily reduce service levels. For planning I use 2 to 4 months of design to reach permit submission, Seattle's permit times as a benchmark, 6 to 10 months for a new house (about 2 to 3 months for a remodel), 12 to 18 months of construction and 18 to 30 months from design start to occupancy; critical areas and lake frontage push toward the long end. The sequence is in my custom home timeline.

As planning ranges: new custom construction $400 to $900 per square foot, whole house renovation $300 to $550, additions $350 to $650, demolition typically $20,000 to $50,000, and a fixed fee for design and permit of about $10,000 to $200,000 depending on scope. Whether to keep the house is covered in remodel or tear down.

My first step on a Sammamish lot is one site plan with the survey, setback tier, net lot area, hardscape budget and trees to keep. Piper Cole designs houses and administers construction on your behalf; the firm does not build.

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