When a remodel counts as a new house: the Eastside thresholds, city by city

There is no single line. Each Eastside city measures something different, so a remodel stops being a remodel at a different point in each. Clyde Hill counts dollars, with a 2026 line of $493,000. Medina and Issaquah count a share of the house’s value, and Bellevue compares remodel cost with replacement value over three years. Mercer Island counts the length of exterior wall you take down, and Kirkland asks which roofs and walls you structurally alter. Seattle and Sammamish set no cost or wall percentage. Past a line, the grandfathered setback or height usually ends and today’s rules apply; Issaquah sends the project to new-development review instead.

At a budget of $750,000 or more you can cross several of these lines. Rules below are from city codes and documents read on 7 October 2026. This is general information, not legal advice, and numbers move, so confirm with the city.

Four separate tests, not one

“Becomes a new house” is shorthand for four unrelated rules, and each applies on its own terms:

• Zoning. Whether the house may keep a setback, height or coverage that today’s code no longer allows.
• Building code. Whether the work counts as a substantial alteration and brings exit, alarm and seismic upgrades.
• Energy code. Which parts of the house must meet the current standard.
• Shoreline. Whether a house near the water keeps the position it has.

A remodel can clear one and fail another, so I check all four.

City by city: what triggers it and how it is measured

A nonconforming house was legal when it was built and no longer meets today’s setbacks, height or coverage. The tests below decide when that protection ends. They matter mainly if your house is in that position.

City	What triggers it	How it is measured	Source
Seattle	No cliff. A nonconforming house may be renovated, structurally altered or rebuilt, but not expanded in a way that increases the nonconformity.	No cost or wall percentage. A rebuild needs a survey or documentation the director accepts, and action toward it must start within 12 months of demolition.	SMC 23.42.112
Bellevue	In the LL, SR and LDR-1 districts, alterations worth more than the replacement value of all primary structures bring the house and site to full compliance. Work below that must itself conform. The 2026 text I read drops the old 30 percent site tier and the setback-extension allowance.	Value of alterations over the preceding three years against replacement value (cost to replace, minus deferred maintenance).	LUC 20.20.561
Kirkland	Structurally altering a roof or exterior wall that does not meet the height or yard standards means that part must conform. Other nonconformances must be corrected above a cost line.	Which walls and roofs you alter. For other nonconformances, work above 50 percent of replacement cost in a consecutive 12 months.	KZC 162.35(7) and (13)
Mercer Island	A nonconforming detached house loses its status if more than 40 percent of its exterior wall length is structurally altered.	Wall segments completely demolished, divided by total wall length. Cumulative over five years, including the five years before the permit.	MICC 19.01.050(D)(1)(b)
Medina	A nonconforming house loses its rights on substantial destruction, and later work must bring the whole structure to current regulations. A house that misses a zoning setback may be rebuilt on its footprint if the permit application follows within six months.	Cost to restore at 60 percent or more of fair market value, damage of any origin. Reconstruction is 60 percent of replacement cost, all phases counted through 18 months after the permit is finalized.	MMC 16.36.060; 16.12.190 and 16.12.200
Clyde Hill	A substantial remodel puts the whole property, existing structures included, under current setbacks, height, coverage and drainage rules.	Project value above $493,000 for 2026, counting projects within two years. Demolishing 75 percent of fair market value during a remodel has the same effect.	City 2026 zoning handout; CHMC 17.60.030
Issaquah	At 75 percent or more of assessed improvement value, a change is reviewed as new development of the site. Every change must reduce the nonconformity as far as practical. A demolished structure must conform.	Remodel cost against King County assessed improvement value.	IMC 18.214.050, .070, .100
Sammamish	No cost or wall percentage found. Changes to a nonconformity must not expand it or create a new type, and must be maintenance or correct it.	The 50 percent figure applies to damaged or destroyed structures; single-family homes are exempt.	SMC 21.09.130

Sources, read 7 and 8 October 2026: Seattle, Mercer Island and Medina on Municode; Issaquah in Ordinance 3013 (effective June 1, 2023) on the city clerk’s site; Sammamish in the city’s published development code; Clyde Hill in the city’s 2026 Residential Zoning Rules handout and a published copy of chapter 17.60; Bellevue in Ordinance 6906 as posted for the 17 March 2026 council meeting, which repeals LUC 20.20.560 and rewrites 20.20.561 (the city says council approved it; I could not read the codified section or effective date), and the city’s 2018 Value of Improvements form; Kirkland in a published copy of KZC chapter 162, current through Ordinance 4905 (2025). Confirm with your city.

Mercer Island and Kirkland: count walls

Mercer Island ignores cost. The city divides the length of existing exterior wall you structurally alter by the total length of exterior wall, and a wall plane counts once any part of it is removed completely, down to no structure. The code’s own example is a 50 foot cube: 200 feet of wall, so 40 percent is 80 feet. One full wall uses 25 percent (50 / 200); a second takes you to 50 percent and the whole house must meet current code. Replacing a roof is not wall alteration, and an interior remodel of any cost is allowed if nothing outside changes. Work from the five years before your permit counts, so an earlier remodel has already spent part of the 40 percent.

Raising the part of a house that already sits inside a yard counts as making the nonconformity worse, with narrow exceptions. More in my Mercer Island guide.

Kirkland sets no percentage for the part of a house already in a yard or above the height limit. Structurally altering a roof or exterior wall that misses the height or required yard standards means that wall or roof must be brought into conformance; repair and maintenance of structural members is excepted. So the question is which walls and roofs you touch: a wall inside the side yard cannot simply be rebuilt in place. See my Kirkland zoning guide.

Clyde Hill, Medina, Issaquah and Bellevue: count value

Clyde Hill uses a dollar figure: $493,000 for 2026, reset each January, using the value the building official puts on the project and adding projects within two years. The city’s valuation counts all labor, materials, overhead and profit, finish work and building systems, so it is close to your whole construction budget. My Clyde Hill guide has the rest.

Medina uses 60 percent. The code defines substantial destruction as damage of any origin, voluntary or not, costing 60 percent or more of fair market value to restore, and reconstruction as construction above 60 percent of replacement cost, counting every phase needed for a habitable building. I plan as if both apply and ask the city how it will count a planned remodel. See my Medina guide.

Issaquah uses 75 percent of the King County assessed improvement value. Below it, a change to a nonconforming structure gets a Level 1 review; at 75 percent or more it is reviewed as new development of the site. At either level the change must reduce the nonconformity as far as practical and feasible. See my Issaquah guide.

Bellevue adds up the value of alterations over the preceding three years and compares it with the replacement value of all primary structures; in the LL, SR and LDR-1 districts that is the line. Replacement value is the cost to replace, minus deferred maintenance, estimated by someone the Director accepts. Ordinance 6906 repealed the older section, which had a 30 percent site tier. The city’s 2018 form describes the older method; confirm which applies. See my Bellevue zoning guide.

Here is what those percentages mean at seven-figure budgets, as planning arithmetic and not advice. It treats your whole budget as the cost the city counts, which overstates some tests. To stay under a line, the house’s value on that test’s basis has to reach the figure shown (budget divided by the share, for example $750,000 / 0.75 = $1,000,000):

Test	Line	Value needed at $750,000	Value needed at $1,000,000
Bellevue	100 percent of replacement value, three years	At least $750,000	At least $1,000,000
Issaquah	75 percent of assessed improvement value	More than $1,000,000	More than $1,333,333
Medina	60 percent of fair market value or replacement cost	More than $1,250,000	More than $1,666,667
Kirkland	50 percent of replacement cost, 12 months (other nonconformances)	At least $1,500,000	At least $2,000,000
Clyde Hill	$493,000 flat, two years	No house value gets under it	No house value gets under it

For scale, at my planning range of $300 to $550 per square foot for whole house renovation, $750,000 is about 1,364 to 2,500 square feet ($750,000 / $550 = 1,364; $750,000 / $300 = 2,500).

Seattle and Sammamish: no cost line

Seattle’s code says its rules are meant to let most nonconformities continue (SMC 23.42.100). A nonconforming structure may be maintained, renovated, repaired or structurally altered, and a residential one rebuilt or replaced, as long as nothing is expanded in a way that increases the nonconformity. A rebuild needs a licensed surveyor’s survey or documentation the director accepts, and action toward replacement must start within 12 months of demolition (SMC 23.42.112). Seattle’s catches are in the building code, below. My Seattle zoning guide and the remodel or tear down guide cover the rest.

Sammamish also has no cost or wall-length test that I found. Changes to a nonconformity must meet all code requirements, must not expand it or create a new type, and must be routine maintenance or correct it (SMC 21.09.130(F)). The chapter does not say how a voluntary teardown is treated, so I ask the city. See the Sammamish guide.

Building code and energy code

Seattle’s residential code lets the building official treat remodeling or additions that substantially extend the useful physical or economic life of the building, or a significant part of it, as a substantial alteration (SRC R107.5.1.1). There is no number. A house classed that way must meet current rules for escape openings, egress, smoke and carbon monoxide alarms and dwelling unit separation, plus seismic upgrades (R107.5.1.2). In a mapped flood hazard area, work worth 50 percent or more of market value is a substantial improvement, and Seattle counts all improvements over five years (R105.7.3). I have not confirmed an equivalent clause in the other cities, so I ask at the first meeting. The million dollar remodel guide goes deeper.

The energy code does not turn a big remodel into a new house. Alterations must meet the new construction standard for the parts altered, and unaltered parts need not comply (WAC 51-11R-50300; the Seattle Energy Code reads the same). Two things pull more of the house in. Space that was not heated and becomes heated, such as a garage or basement, must fully comply (R502.2), and an addition over 150 square feet that adjoins an existing attic brings that attic under the envelope requirements (R502.3.1.1). See my Washington energy code guide.

On the water, the tests change again

Shoreline rules sit on top of zoning and measure differently. Medina’s zoning test counts cost, while its shoreline program counts removal of more than 60 percent of the exterior wall framing by length, so a lake house there has to pass both (MMC 16.60.228). Seattle’s shoreline code counts work in any five years costing 60 percent or more of market value, measured on the nonconforming part where one exists, and bars substantially improving or replacing a house inside the shoreline setback except after a casualty (SMC 23.60A.124 and 23.60A.936). The city-by-city table is in my waterfront remodel guide.

How I scope and phase a remodel around the line

I run the same six steps in every city before design starts:

1. Map the nonconformity. Draw today’s setbacks, height and coverage over the survey and the house, and list what sits outside them. If nothing does, no test applies.
2. Pick the city’s measure. Walls in Mercer Island, walls and roofs in Kirkland, value in Clyde Hill, Medina, Issaquah and Bellevue.
3. Decide what stays. Keep the nonconforming walls and roof in place and add volume on the conforming side.
4. Settle the valuation basis. Ask which number the city will use. In Bellevue the estimator and method set the ratio.
5. Check the windows. Mercer Island looks back five years, Bellevue counts three, Clyde Hill two and Kirkland 12 months. Medina counts every phase through 18 months after the permit is finalized. A pause longer than the window can keep each permit under a line, at the price of two permit cycles. I ask the city in writing how it will count.
6. Price the rebuild beside it. New custom construction runs $400 to $900 per square foot as a planning range, plus demolition typically $20,000 to $50,000. In Seattle a rebuild can keep the nonconforming footprint (SMC 23.42.112); in Issaquah a demolished structure must conform.

The wider choice is in remodel or tear down and rebuild. Sometimes crossing the line is the right call, and it is better decided before design than found at permit review.

Where the check happens

The free feasibility check usually takes about a day. I check the lot, the existing house against today’s rules, and which thresholds your plan would reach. An in-depth analysis is $1,500 and takes 2 to 3 weeks: wall counts, valuation math, and the remodel and rebuild side by side.

After that I quote a fixed fee to design and permit, set by the project budget and location. Design to permit submission typically takes 2 to 4 months, and in Seattle a remodel permit can be obtained in about 2 to 3 months. The remodels I take on start at a project budget of $750,000. Piper Cole designs and administers construction; it does not build.

Questions

At what point does a remodel count as a new house?

There is no single line. Clyde Hill’s substantial remodel threshold is $493,000 for 2026. Medina’s is 60 percent of fair market value, Issaquah’s 75 percent of assessed improvement value, Bellevue’s 100 percent of replacement value over three years, and Mercer Island’s 40 percent of exterior wall length over five years. Kirkland looks at which walls and roofs are structurally altered. Seattle and Sammamish set no cost or wall percentage. These tests apply when the house is nonconforming. Confirm with your city.

What is a nonconforming house?

A house that was legal when it was built but no longer meets today’s setbacks, height or coverage because the code changed. Cities let it continue and be maintained, but each limits how much it can be altered before it must meet current code. A house built without meeting the rules in force at the time is not legally nonconforming.

What is Mercer Island’s 40 percent rule?

Under MICC 19.01.050, a legally nonconforming detached house keeps its status only while no more than 40 percent of the length of its existing exterior walls is structurally altered, counted cumulatively over five years including work in the five years before the permit work. A wall plane counts once any part of it is removed completely, down to no structure. Beyond 40 percent the whole house must meet current code. Roof replacement and interior remodeling do not count.

What is Clyde Hill’s substantial remodel threshold?

The 2026 threshold is $493,000 of project value as determined by the building official, and it changes each January. Projects within two years are added together. Past it, the whole property, including existing structures, must meet current setbacks, height, coverage and drainage rules, and a variance may be needed to keep a nonconforming structure. Demolishing 75 percent of the building’s fair market value during a remodel has the same effect.

Does Seattle limit how much I can remodel a house that sits inside a setback?

Not with a cost or wall percentage. SMC 23.42.112 lets a nonconforming structure be renovated, repaired or structurally altered, and a residential one rebuilt, as long as the nonconformity is not expanded. Seattle’s building code is separate: the building official can classify a remodel that substantially extends the life of the house as a substantial alteration, which brings escape openings, alarms and seismic work into scope.

Does phasing a remodel avoid these thresholds?

Sometimes, because the windows differ: five years on Mercer Island, three years in Bellevue, two years in Clyde Hill and 12 months for Kirkland’s cost test. Medina counts every phase needed to make a habitable building through 18 months after the permit is finalized, and Seattle counts five years of improvements in a flood hazard area. Phasing also means two permit cycles. Ask the city in writing how it will count before you plan around a gap.

Does a big remodel make the whole house meet the energy code?

No. Under the Washington State Energy Code, alterations must meet the new construction standard for the parts altered, and unaltered parts need not comply. Space that was unheated and becomes heated must fully comply, and an addition over 150 square feet that adjoins an existing attic brings that attic under the envelope requirements.

How does Bellevue value a house for its remodel test?

The 2026 ordinance text compares the value of alterations over the preceding three years with the replacement value of all primary structures on the site, defined as the cost to replace the structure minus deferred maintenance. The applicant uses a cost estimator the Director accepts. The city’s 2018 form, for the older rule, allowed assessed value. Confirm the method with the city.