Sammamish and Issaquah architect: find out what your lot allows before you design

Before you hire a Sammamish architect or an Issaquah architect, know this: each city’s rules decide how much house your lot can take before anyone draws a line. They set the floor area and hard surface the lot may carry, how close to the lot lines the house may stand, how tall it may be, and what trees, steep slopes and Lake Sammamish add on top. The two cities use different tests, so I treat them one at a time. My first basic feasibility check is free and very quick, usually about a day: send me the address and what you are thinking of building. An in depth analysis is $1,500, takes 2 to 3 weeks and goes further than the first check. I design and administer construction; I do not build.

Who this page is for

This page is for an owner or buyer of a house or lot in the City of Sammamish or the City of Issaquah, Washington, who is choosing an architect for a remodel, an addition or a new house. The rules differ by city, so each city has its own sections and sources below, and none of one city’s numbers applies to the other. The sources for this page were read on 9 November 2026. Both cities keep their municipal code on a site behind a bot check, which was not bypassed, so current code text was not read there. Ordinance copies and a January 2024 revision of the Sammamish code are labelled where used. The code in force controls, so confirm every number with the city. This is general information, not legal advice.

Sammamish home addition and remodel: the permit path and the standards

The path. The Permit Center page says all applications are processed online at MyBuildingPermit.com. The city’s residential addition checklist asks for a critical area affidavit, a plan set, a site plan, structural calculations, a site protection plan and a drainage review checklist; its remodel checklist asks for a plan set showing the house as-is and as proposed. The addition checklist says the city may add an arborist report and a geotechnical report. The permitting process sheet says an application is screened within four working days, review times vary with scope and permit volume,. It gives no single family review time.

The standards. The city’s R-4 development standards page lists a floor area ratio of 50 percent, hardscape coverage of 40 percent, a building height of 35 feet, a sidewall height of 24 feet and at most 3,000 square feet of upper level floor per building. A city copy of Ordinance O2026-594 (marked final; its effective date was not confirmed) adds a one time 300 square foot expansion of upper level floor per building, which the R-4 page does not mention. The yards depend on the size of the building:

Building size (R-4)	Front yard	Side yard	Rear yard
Less than 2,500 square feet	15 feet (30 on arterial streets)	5 feet	15 feet average, 12 minimum
2,500 to 4,000 square feet	20 feet (30 on arterial streets)	10 feet average, 8 minimum	20 feet average, 15 minimum
Greater than 4,000 square feet	25 feet (30 on arterial streets)	12 feet average, 10 minimum	25 feet average, 20 minimum

The R-4 page does not say how building size is measured. The city’s floor area ratio page counts the area of a building including the exterior walls, not uncovered overhangs, decks and balconies, says expanding a home past the limit needs a zoning variance, and does not mention garages. The hardscape page counts impervious surface, gravel, areas that preclude vegetation, and areas under overhangs of more than 18 inches. For other zones see my Sammamish zoning guide.

Sammamish: one lot worked line by line

The lot is hypothetical, not a real property or a client’s: zone R-4, 90 by 121 feet, which is 10,890 square feet (90 x 121), flat, on a local street, with no critical area or shoreline. The house is one story, 50 by 46 feet, 2,300 square feet including an assumed 400 square foot attached garage. The driveway is 600 square feet, the walk 150 and the patio 300. This page counts roofs as hardscape and the garage as floor area; the city’s pages state neither, so ask. The owner wants a 20 by 25 foot ground floor addition, which is 500 square feet.

Rule	What the city says	On the hypothetical lot
Floor area ratio	50 percent of the lot	10,890 x 0.50 = 5,445. Now 2,300 (21.1 percent). With the addition 2,800 (25.7 percent). Room left: 2,645
Hardscape	40 percent of the lot	10,890 x 0.40 = 4,356. Now 2,300 + 600 + 150 + 300 = 3,350 (30.8 percent). With the addition 3,850 (35.4 percent). Room left: 506
Yard tier	Set by building size, which the page does not define	2,300 is under 2,500; 2,800 is over it. If the whole building sets the tier, the front yard asked for rises from 15 to 20 feet, and a house standing 17 feet back meets the first and misses the second

The first limit this lot meets is the yard tier, and only if the city counts the whole building, garage included, toward the tier; that is the first question for the city’s Project Guidance service. A second option adds a remodel that removes more than half of the exterior walls. The footnote on the city’s housing page defines demolition for a residential building as the removal of more than 50 percent of exterior walls. A copy of code amendment attachments on the city’s agenda site, which prints no ordinance number, adds that a wall counts as removed when its structure is removed or moved, or when it is enclosed behind newly constructed space. The housing page lists O2026-597 as its current ordinance since 29 August 2026; that ordinance was not read, so the test is as the housing page prints it today. The house has 2 x (50 + 46) = 192 feet of exterior wall, so more than 96 feet crosses the line; the addition, joined along a 25 foot wall, encloses 25 / 192 = 13.0 percent. The definition does not say whether the 50 percent counts wall length or wall area.

The city’s affordable housing page says additions to existing dwellings are exempt from its inclusionary program, but a project removing more than 50 percent of the exterior walls is reconstruction, not an addition; involuntary reconstruction is exempt. For reconstruction it takes finished living space, which excludes garages, less an exempt area (1,750 square feet on that page) and charges a fee in lieu on the rest. Taking the assumed 400 square foot garage out of the 2,800 leaves 2,400, and 2,400 to 1,750 = 650 square feet. Confirm the exempt area with the city. My guide to when a remodel counts as a new house covers other cities.

Sammamish: an older house, slopes, trees and the lake

An older house. In the city’s revision of the code issued 23 January 2024 (effective 1 January 2022), a modification to a nonconforming structure must comply with all code requirements and may not expand the nonconformance. In the amendment attachments noted above, nonconformance status is forfeited by demolition and is not re-established.

Slopes. The code’s landslide hazard areas include slopes of 40 percent or steeper with 10 or more feet of vertical relief: 10 feet of rise over 25 feet of run is 10 / 25 = 40 percent. The city’s clean copy of its 2024 critical areas update sets a 50 foot buffer from the top and toe, which a critical areas report can reduce. See my hillside lot guide.

Trees and the lake. The city’s tree page requires a permit to remove a conifer over 8 inches or a deciduous tree over 12 inches across, and any tree in a critical area or buffer; where development is proposed, no tree comes out before the construction permit issues. The page words the sizes both as “exceeding” and “or larger”; ask about a tree at exactly that size. For a new primary residence on an R-4 lot the January 2024 revision requires keeping at least 35 percent of significant trees outside critical areas and buffers. The shoreline page gives a 50 foot shoreline setback on Lake Sammamish from the ordinary high water mark; see my Lake Sammamish guide.

Issaquah home remodel and addition: the permit path and the standards

The path. Issaquah takes building permits online at MyBuildingPermit.com and accepts no paper applications. Its Remodel page covers interior remodels; additions go through its New Construction and Addition page. The submittal packet (last update August 2023) lists a letter of water and sewer availability, a traffic concurrency certificate and an approved King County septic permit (the last two where they apply) as requirements before submitting, and says a pre-submittal meeting may be required. It also asks for a geotechnical report and a stormwater report. The target review times sheet (April 2026) lists a single family permit at 4 weeks for a first review, 3 for a second and 1 for later ones, counted from payment of fees: 4 + 3 + 1 = 8 weeks for three reviews.

The standards. Table 18.404.090(A), read in Ordinance 3088 (effective 29 April 2025), gives for three single family zones:

Limit	SF-E	SF-S	SF-SL
Minimum lot size	35,000 square feet	9,600 square feet	6,000 square feet
Front setback	30 feet	20 feet	10 feet
Side setback	15 feet	8 feet	6 feet
Rear setback	30 feet	10 feet	20 feet
Maximum impervious surface	30 percent	40 percent	50 percent
Base building height	30 feet	30 feet	30 feet

A floor area ratio is used in some zones in Central Issaquah, Talus and Issaquah Highlands, not in these. The impervious surface rule (Ordinance 3015, effective 1 June 2023) adds the footprint of buildings, driveways, sidewalks, decks, patios, porches, pools and overhangs of more than 18 inches, and notes site constraints can cap a lot below the maximum.

Issaquah: height, an older house, trees, slopes and the lake

Height. Ordinance 3067 (effective 30 July 2024) measures from the average of existing or finished grade, whichever is lower, to the midpoint of the highest gable on a 4:12 to 12:12 roof, or the coping of a flat roof, with spot elevations every ten feet around the footprint. On hillsides of 15 percent slope and 10 feet of rise, the hillside chapter measures from existing grade with no averaging. See my existing conditions guide.

An older house. Under IMC 18.214 (Ordinance 3013, effective 1 June 2023), a legal nonconforming single family structure may be expanded so long as the nonconforming part is not increased and the change meets the approval criteria of IMC 18.214.070(C), and anything built after a demolition must conform. A remodel of a nonconforming structure costing under 75 percent of the King County assessed improvement value may be permitted through a Level 1 review; at 75 percent or more it goes through the review for new development.

Trees and slopes. The tree retention rule (Ordinance 3114, effective 14 October 2025; the exhibit is a markup copy) requires keeping 35 percent of the total caliper of significant trees in the developable site area when a residential project expands the footprint or impervious surface. Four hypothetical trees of 12, 16, 20 and 24 inches total 72, so 72 x 0.35 = 25.2 inches must stay; trees rated poor or hazardous do not count. A significant tree is six inches across (eight for alder and cottonwood), and the tree permit page says most removals need a permit. The steep slope rule (Ordinance 3019, effective 1 June 2023) sets a 50 foot buffer from the top and toe of a slope of 40 percent or more, reducible to 10 feet by study, plus a 15 foot building setback and an occupied building at least 25 feet from the top or toe: 10 + 15 = 25.

The lake. Issaquah’s shoreline program (consolidated copy), as amended by Ordinance 3089, puts new residential development on Lake Sammamish landward of a 35 foot buffer plus a 15 foot building setback, 35 + 15 = 50 feet from the ordinary high water mark. Expanding an existing house needs no shoreline variance if the expansion is landward of the buffer, and of the building setback where part of the house stands waterward of both. Ecology lists the amended program as effective 26 May 2025. For the rest, see my Issaquah zoning guide.

What to send me

The address or parcel number is enough to start. It helps to add:

• A remodel, an addition or a new house, and the changes you want.
• Any survey, existing drawings or permit history, and whether the lot has a slope, a stream or the lake.
• Whether you are buying, and when your inspection period ends.

How it works with me

The first basic feasibility check is free and very quick, usually about a day. If you want more, an in depth analysis is $1,500, takes 2 to 3 weeks and goes further than the first check. If you go ahead, my fee for design and permit is fixed and agreed before design starts. Design to permit submission typically takes 2 to 4 months. After the permit I administer construction for you; I do not build.

I have been an architect since 1996, and I am a member of the AIA (since 1992) and NCARB (since 1996).

Questions

How do I choose a Sammamish architect or an Issaquah architect for a remodel, an addition or a new house?

Ask each architect for your lot’s numbers before design: the floor area, hard surface or impervious limit, yards, height, slope and tree rules of your own city, because Sammamish and Issaquah use different tests. Ask how the fee is set and who administers construction. My fee is fixed and agreed before design starts, and I administer construction; I do not build. Washington’s architect licensing chapter exempts design work on a residential building of up to and including four dwelling units (RCW 18.08.410(5)), so the choice is yours.

What can I build on my Sammamish lot?

In R-4 the city’s page lists a floor area ratio of 50 percent, hardscape coverage of 40 percent, a height of 35 feet and a sidewall height of 24 feet, with yards that grow with the size of the building. On a 10,890 square foot lot that is 5,445 square feet of floor area and 4,356 of hardscape. Other zones, steep slopes, trees and the lake add review, so confirm with the city.

When does a Sammamish remodel count as demolition?

The city’s housing page defines demolition of a residential building as the removal of more than 50 percent of its exterior walls, and a code amendment copy adds that a wall counts as removed if it is removed, moved, or enclosed behind newly constructed space. The housing page says such a project is reconstruction, not an addition, for its inclusionary housing program; demolition also ends nonconforming status. The definition does not say whether length or area is counted, so ask.

What can I build on my Issaquah lot?

In SF-S the table allows 40 percent impervious surface, a 20 foot front setback, 8 foot sides, a 10 foot rear and a 30 foot base height; SF-E allows 30 percent and SF-SL 50 percent. Building footprints count as impervious surface. Those zones have no floor area ratio. Hillsides, critical areas, trees and Lake Sammamish add rules; check the current code with the city.

How long does a building permit take in Sammamish and in Issaquah?

Issaquah’s April 2026 target sheet lists 4 weeks for a first review of a single family permit, 3 for a second and 1 for third and later ones, counted from payment of permit fees. Sammamish’s process sheet says applications are screened within four working days and that review times vary with scope and volume; it posts no single family figure. Actual times vary.

Do I need a permit to remove a tree in Sammamish or Issaquah?

Often yes in both. Sammamish requires a permit for significant trees (conifers over 8 inches, deciduous over 12 inches) and any tree in a critical area or buffer. Issaquah says most removals need a permit; a significant tree is six inches or more, eight for alder and cottonwood, with replacement of at least one tree for each removed. Issaquah also requires keeping 35 percent of significant tree caliper on residential redevelopment that expands the footprint.

What does a home addition cost in Sammamish or Issaquah?

It depends on the drawings, so I give no figure on this page; see my home addition cost guide. The cities also publish fee schedules, which my Sammamish and Issaquah fee guides explain.

What does the feasibility check cost, and do you build?

The first basic feasibility check is free and very quick, usually about a day. An in depth analysis is $1,500 over 2 to 3 weeks. If you go ahead, I quote a fixed fee for design and permit, agreed before design starts. Piper Cole Architects designs and administers construction. We do not build.