Whole house remodel architect on Mercer Island

Short answer: if you own a house on Mercer Island, lake lot or upland lot, and your remodel budget starts at $750,000, I offer a free first feasibility check that takes about a day, then a fixed fee for design and permit set by your budget and location. On the island, a handful of city rules decide how far a remodel can go before anyone picks a finish: the 40 percent exterior wall rule, lot coverage and hardscape limits, the tree code, and the slope or shoreline conditions on your lot. Your architect should be able to show you where each one sits on your site plan before you pay for full drawings.

This page is for owners comparing architects for a whole house remodel or a major remodel with an addition. The rules below come from the Mercer Island City Code and the city’s own permit pages, read on 8 October 2026. Confirm with the city before you rely on a number. For zoning and process in general, see my Mercer Island building permit and zoning guide.

The 40 percent wall rule

Many Mercer Island houses sit closer to a lot line than today’s yards allow. That is legal, and the code calls the house nonconforming. Under MICC 19.01.050(D), a legally nonconforming detached house can be altered or enlarged without losing that status only while no more than 40 percent of the length of its existing exterior walls is structurally altered. Cross the line and the whole structure has to meet current code, including setbacks. Even under 40 percent, the code says the work may not increase any existing nonconforming aspect or create a new one.

The code gives the arithmetic. The percentage is the length of wall segments completely demolished divided by the total length of exterior wall segments. A segment counts as completely demolished when any portion of it is removed so that no structural elements remain, and each bay or bump-out counts as its own wall plane. The code’s example: a 50 foot cube has 200 feet of wall, or 214 feet with a two by ten foot bay. The clock is five years, and it includes the work in your permit plus work done in the five years before it. Replacing a roof does not count as altering the walls, and neither does interior remodeling of any cost when no exterior alteration or enlargement is involved. The code also excludes replacing exterior cladding and glazing in existing openings.

Work on a 50 foot cube house (200 feet of wall)	Wall length counted	Share of 200 feet	Where that leaves you
One wall fully rebuilt	50 feet	25 percent	Under the 40 percent limit of 80 feet
Two walls fully rebuilt	100 feet	50 percent	Over the limit; the house must meet current code
One wall rebuilt now, and one rebuilt under a permit three years ago	100 feet	50 percent	Over the limit, because the five year look-back counts earlier work
New roof, new siding, new windows in the same openings, full interior remodel	0 feet	0 percent	No wall count, as long as the roof does not expand the nonconformity

The percentages are my arithmetic on the code’s 200 foot example; the counting rules are from MICC 19.01.050(D)(1)(b). A real house has more wall segments than a cube, so the count has to be done on your drawings.

Two more points matter in design. Raising the part of a house that intrudes into a required yard counts as increasing the nonconformity unless the added height meets today’s yard, with narrow exceptions such as a flat roof becoming a pitched one. And because a wall segment counts whole once any portion is removed completely, ask the city how it will count a large new opening before the design is fixed.

If the plan you want crosses 40 percent, I price the remodel next to a rebuild to current setbacks and compare them honestly. The general version of that decision is in when a remodel counts as a new house, and the demolition side is in demolition permits for a teardown.

Coverage, floor area and height apply to remodels too

The city’s lot coverage section applies to single-family development including the remodeling of existing houses, so a remodel that adds a deck, terrace or garage is measured like a new house (MICC 19.02.020).

• Lot coverage. House, driving surfaces and accessory buildings may cover 40 percent of the net lot on a slope under 15 percent, 35 percent from 15 to under 30 percent, 30 percent from 30 to 50 percent, and 20 percent above 50 percent.
• Hardscape. Walkways, decks and patios are capped at 9 percent of net lot area: 900 square feet on a flat 10,000 square foot lot, the code’s own example. A lot of 8,400 square feet or less may use the lesser of 755 square feet or 12 percent. A pool cannot sit in a front yard or within five feet of an adjacent property, measured from the edge of the water (MICC 19.02.070). The permit side is in the swimming pool permit guide.
• Floor area. Gross floor area is capped at 5,000, 8,000, 10,000 or 12,000 square feet in R-8.4, R-9.6, R-12 and R-15, or 40 percent of the lot area, whichever is less. Ceilings from 12 to 16 feet count at 150 percent of their floor area and ceilings above 16 feet at 200 percent, so a double-height great room uses more of the allowance than it appears to.
• Height. 30 feet above the average building elevation to the highest point of the roof, and 30 feet on the downhill facade of a sloping lot.

One thing that does not apply: the design standards chapter (MICC 19.12) covers regulated improvements, a term the code defines to exclude single-family dwellings. A house remodel falls under the residential rules above instead.

Trees, slopes and the lake

Trees. An addition or remodel that adds more than 500 square feet of gross floor area on a lot of 6,000 square feet or more must retain at least 30 percent of trees 10 inches or larger over a rolling five years, and must keep exceptional trees of 24 inches or more except in narrow cases (MICC 19.10.060). Removed trees are replaced at 1 to 6 trees each. The city says the answer to whether you need a tree permit is almost always yes, and its residential permit submittals ask for a tree inventory form and a tree plan. A lot that has lost more than 70 percent of its large trees in five years cannot be approved until it complies, so clearing ahead of design backfires. I want the arborist survey before the plan is set.

Slopes. The city says it is very common for an island project to alter a mapped geologic hazard. Those areas require a geotechnical report by a Washington licensed engineer, and critical area work triggers an intake screening at any project size. Clearing, grading, filling and foundation work in a landslide hazard area, or disturbing 2,000 square feet or more in an erosion hazard area, is not allowed from October 1 to April 1 unless the city grants a waiver backed by a critical area study (MICC 19.07.160). New foundation work has to be scheduled around that window. Check the city’s hazard map layers before you design.

The lake. Structures, including fences over 48 inches, sit at least 25 feet from the ordinary high water mark. Hardscape and coverage are capped at 10 percent within the first 25 feet and 30 percent from 25 to 50 feet, and height never exceeds 35 feet (MICC 19.13.050). A legally built structure within 25 feet landward of the water may be maintained, remodeled and even completely replaced as long as the nonconformance is not increased, and an expansion is allowed if the new part complies (MICC 19.13.020). Add 500 square feet or more of floor area, coverage or hardscape, counting the previous five years, and native vegetation must cover 50 percent of a 20 foot strip along the water, or 75 percent at 1,000 square feet, under an approved plan.

An owner-occupied single-family house no higher than 35 feet is exempt from the shoreline substantial development permit, but the city still requires a shoreline exemption application, the standards still apply, and conditions can include a monitored planting plan. As I read the code, two sets of rules apply side by side: the shoreline allowance covers the shoreline standards, while side and front yards still follow the 40 percent wall rule. More in the shoreline exemption guide and my waterfront remodel guide.

What changes the cost and the schedule

These are planning ranges and published fees, not quotes; a builder’s bid on finished drawings is the price.

Item	Planning figure	What moves it
Whole house renovation, construction	$300 to $550 per sq ft	Structure, systems, layout changes, site access
Additions, construction	$350 to $650 per sq ft	New foundation, roof and envelope
What $750,000 of construction covers	About 1,364 to 2,500 sq ft	$750,000 divided by $550 and by $300
My fee for design and permit	Fixed fee, about $10,000 to $200,000	Set by project budget and location
City building, plan check and combination permit fees at $750,000 of value	About $15,074	Project valuation; additional review lines are extra
Design to permit submission	2 to 4 months	Scope, consultants, how quickly decisions are made

The permit fee arithmetic comes from the 2026 Mercer Island fee schedule (Resolution 1698, effective August 1, 2026). The building permit fee for $750,000 is $5,547.09 for the first $500,000 plus $7.81 for each additional $1,000, which is $7,499.59. Plan check is 70 percent of that, $5,249.71, and the combination fee for mechanical, electrical and plumbing inspection is 31 percent, $2,324.87, for $15,074.17 in all. That total is not like for like with Seattle’s fee. The city validates your stated valuation against its own table, and review lines such as arborist review ($427), residential alteration energy compliance ($261) and the intake screening ($903) come on top. I read the schedule on 8 October 2026; recheck it when you budget.

What moves the cost on the island is mostly the list above. Crossing 40 percent turns a remodel into a rebuild to current setbacks. A shoreline planting plan, tree replacement, a geotechnical report and a wet season restriction each add a consultant, a review or a month. Stormwater drainage review applies at a net 500 square feet of new impervious surface, 2,000 square feet of new plus replaced hard surface, or 7,000 square feet of land disturbance, and roof area counts as replaced hard surface once any part of the wall below it is removed to the foundation and rebuilt. A project over 6,000 square feet overall, or adding more than 3,000, needs a construction management plan. Found at feasibility, none of these is a surprise. For the budget logic, see how I plan the spend on a seven-figure remodel.

What to ask any architect before you sign

1. Is the fee fixed, and what is in it? Ask whether the survey, engineers, arborist and city fees sit inside or outside the number.
2. Who draws my house and who answers my calls? Ask for a name.
3. Can you show me the 40 percent wall count on my drawings before design starts? A general statement means the work has not been done.
4. Which of my lot’s constraints will set the design? A good answer points to the shoreline line, tree survey or slope map on a site plan.
5. What does the feasibility step cost and what do I get? Mine is free and takes about a day, and the in-depth analysis is $1,500.
6. How many rounds of city comments does the fee cover? The city charges its hourly rate ($182 on the 2026 schedule) after three rounds of plan review, so ask who pays for round four.
7. What does construction administration include? Ask about site visits, payment requests, change orders and the builder’s questions.
8. Will you help me compare builder bids? Bids compare only when every builder prices the same drawings and allowances.

How the work goes, in order

Step	Typical time	What you get
Free feasibility check	Very quick, about a day	Whether the plan fits your lot, the rules above and your budget, at a basic level
In-depth analysis (optional)	2 to 3 weeks, $1,500	A deeper look at zoning, the wall count and budget before full design
Design to permit submission	2 to 4 months, fixed fee	Drawings, engineering and the permit set
Intake screening	2 weeks target	Required for additions of 500 square feet or more of footprint, critical area work, and net new impervious surface of 500 square feet or more; comments, not a pass or fail
City review	Routing 1 week; first review 4 weeks (major building permit) or 2 weeks (non-major); 2 weeks per later review; 1 week to prepare the permit	An issued permit; where public notice applies, which the city says includes residential building permits, a 30 day comment period runs and review cannot finish before it ends
Bidding and construction	Set by scope and builder	Builder bids on finished drawings; Piper Cole administers construction for you and does not build

With one round of corrections, the city’s published targets add up to about 10 weeks of city time (intake 2, routing 1, first review 4, second review 2, permit preparation 1), my arithmetic on targets the city calls estimates. Add 2 to 4 months of design and you get roughly 4 to 6 months from design start to an issued permit, longer with a critical area or shoreline review. My 2 to 3 months for a remodel permit is a Seattle figure; Mercer Island runs its own department. My page for the island is architect services in Mercer Island.

I have been an architect since 1996, an AIA member since 1992 and an NCARB member since 1996. I hold three Masonry Excellence Awards for commercial projects, and the Carr residence was featured in Above The Lake and Lux magazines.

Questions

How much does a Mercer Island remodel architect cost?

David Meade quotes a fixed fee for design and permit, set by the project budget and location, typically about $10,000 to $200,000 depending on scope. Remodels start at a project budget of $750,000. The first basic feasibility check is free and takes about a day, and an in-depth analysis is $1,500 over 2 to 3 weeks. City permit fees are separate: on the 2026 Mercer Island schedule, the building, plan check and combination permit fees come to about $15,074 at $750,000 of project value, before additional review lines.

How much of my Mercer Island house can I change without meeting current setbacks?

If the house is legally nonconforming, no more than 40 percent of the length of its existing exterior walls can be structurally altered, counted over five years including work done in the five years before the permit (MICC 19.01.050). A wall segment counts once any portion is removed so that no structural elements remain. Roof replacement and interior remodeling do not count when no exterior alteration or enlargement is involved. Past 40 percent, the whole house must meet current code.

Do I need a shoreline permit to remodel a lakefront house on Mercer Island?

Owner-occupied construction of a single-family house no higher than 35 feet is exempt from the shoreline substantial development permit, but the city requires a shoreline exemption application and every shoreline standard still applies: the 25 foot setback from the ordinary high water mark, the coverage limits near the water, and native planting when you add 500 square feet or more. Conditions can include a mitigation plan with monitoring. Confirm with the city for your lot.

How long does a remodel permit take on Mercer Island?

The city publishes targets rather than guarantees: 2 weeks for intake screening where it applies, 1 week for routing, 4 weeks for the first review of a major building permit or 2 weeks for a non-major one, 2 weeks for each later review and 1 week to prepare the permit. With one round of corrections that is about 10 weeks of city time. Where public notice applies, which the city says includes residential building permits, a 30 day comment period runs and review cannot finish before it ends. Design to permit submission typically takes 2 to 4 months before that.

Can I add a pool or terrace as part of a Mercer Island remodel?

Yes, within the lot rules. Walkways, decks and patios are capped at 9 percent of net lot area, which is 900 square feet on a flat 10,000 square foot lot, and total lot coverage is capped at 20 to 40 percent by slope. A swimming pool cannot be in a front yard or within five feet of an adjacent property, measured from the edge of the water. On a waterfront lot, hardscape and coverage are also capped at 10 percent within 25 feet of the water.

Do I need a tree permit for a remodel on Mercer Island?

The city says a tree permit is almost always needed, and tree work is reviewed with your building permit. An addition or remodel that adds more than 500 square feet of gross floor area on a lot of 6,000 square feet or more must retain at least 30 percent of trees 10 inches or larger over a rolling five years and keep exceptional trees of 24 inches or more except in narrow cases. Removed trees are replaced at 1 to 6 trees each, depending on size, and the city asks for an arborist report when work is within a tree’s dripline.

Does Piper Cole build the remodel too?

No. Piper Cole Architects designs the remodel and administers construction on your behalf. You hire the builder. That separation means the party reviewing the work and the payment requests is not the party building it.

What does a whole house remodel cost per square foot on the Eastside?

Piper Cole uses $300 to $550 per square foot as the planning range for a

whole house renovation

and $350 to $650 per square foot for additions. At those rates, $750,000 of construction covers about 1,364 to 2,500 square feet of whole house renovation. These are planning ranges, not quotes, and exclude design fees, permits and sales tax. A builder’s bid on finished drawings is the real number.