Remodeling a waterfront home on Lake Washington, Lake Sammamish or the Sound: what changes on the water

Short answer: remodeling a house on the water is a normal remodel with a second rulebook on top. Within 200 feet of the ordinary high water mark, your city’s shoreline master program decides how much of the existing house you can change and where an addition can go, and it can require native planting along the water. The biggest question is usually whether the house already sits closer to the water than today’s setback allows. If it does, that grandfathered position is worth protecting, and the design should be built around the limit your city sets.

Rules below are from state law and city codes, read 1 October 2026. Confirm with your city.

The shoreline rules still apply to a remodel

The Shoreline Management Act covers the water and the land within 200 feet of the ordinary high water mark (OHWM). Lake Washington, Lake Sammamish and Puget Sound are all inside it, and each city along them has its own shoreline master program (SMP). Building, remodeling or adding to a house for the owner’s own use is usually exempt from the shoreline substantial development permit if it stays at or under 35 feet above average grade, but the exemption covers the permit only. Setbacks, vegetation rules, height limits and the nonconforming rules still apply. The exemption itself is covered in my guide to shoreline exemptions for a single-family home.

Repair, remodel or expansion: name what you are doing

Shoreline codes sort work into roughly three buckets:

• Maintenance and repair. Fixing what is there in the same size and form. Mercer Island allows ordinary repair of a nonconforming house that creates no new nonconformity, and an interior remodel of any cost or extent if no exterior alteration or enlargement is involved (MICC 19.01.050). Roof repair, including total replacement, does not count as structural alteration of the walls there.
• Remodel and structural alteration. Moving walls, replacing framing, changing the roof form. This is where the city limits start counting.
• Expansion. More footprint, more floor area, more height, more hardscape. Expansion has to meet current rules, and on the water it is what triggers planting.

A major remodel usually does all three. The design move that matters is to keep the part of the house inside the setback in the first bucket and put the expansion where the code allows it.

When the house already sits inside today’s setback

Many lake cabins and waterfront houses predate the current setbacks. A house that was legal when built and no longer meets today’s standard is a nonconforming structure. It can stay. The question is how much you can change before the city treats it as new and makes it meet today’s setback. State rules set a fallback that only applies when a city has no local standards (WAC 173-27-080). Every city below has its own, and they measure the limit differently.

City	What you can do to a house inside the shoreline setback	Where the limit is
Mercer Island	Structures within 25 feet of the OHWM may be maintained, repaired, renovated, remodeled and completely replaced, as long as the nonconformance is not increased. Expansions are allowed if the new part meets the code (MICC 19.13.020).	For zoning nonconformities such as side yards, a house keeps its status only while no more than 40 percent of the length of its existing exterior walls is structurally altered, cumulative over five years. A wall segment counts once any part of it is removed to no structure (MICC 19.01.050).
Medina	A nonconforming structure may be enlarged, remodeled or structurally altered if the work does not increase the nonconformity (MMC 16.66.090).	A house loses its nonconforming rights on substantial destruction, defined in the shoreline program as removing more than 60 percent of the exterior wall framing by length; partial removal along a length counts as removing all of it, though replacing windows or doors does not count when no beams or struts are removed. It can still be rebuilt within its existing footprint and keep the shoreline setback, if any added footprint conforms and a complete building permit is filed within six months.
Kirkland	A nonconforming structure may be maintained, repaired, altered and remodeled without increasing the nonconformity (KZC 83.550).	Structural alteration of a roof or exterior wall that does not meet the shoreline setback or height must be brought into conformance. Window, door and repair work is excepted if floor area does not grow, no wall moves to make things worse, and the cost in any one year stays at or below 50 percent of replacement cost.
Seattle	On dry land outside the setbacks, a nonconforming house may be altered, substantially improved or replaced, without expanding the nonconformity (SMC 23.60A.124).	Development within the shoreline setback or the residential shoreline setback may be maintained, repaired and structurally altered, but not substantially improved or replaced, except after a fire or other casualty. Substantial improvement means work in any five years costing 60 percent or more of market value; for nonconforming development, more than 60 percent of the market value of the nonconforming portion.
Issaquah (Lake Sammamish)	An existing house may be modified or expanded without a shoreline variance if the expansion is landward of the 35 foot buffer (IMC 18.804).	If any part of the house is inside the buffer or the 15 foot building setback behind it, the expansion must go landward of both.

Sources: MICC 19.01.050 and 19.13.020 (Municode, current); Medina MMC 16.66.090 and 16.60.228 (Municode, current); KZC 83.550 as adopted by Kirkland Ordinance 4701 (2020); SMC 23.60A.124 and 23.60A.936 (Municode, current); Issaquah SMP section 6.1.3 (Ordinance 3021, 2023; city edition May 2025). As of 1 October 2026, confirm with your city.

Three details change designs. First, Mercer Island measures wall length and ignores cost, and it counts work from the previous five years, so an earlier remodel uses up part of the allowance. Raising the part of a house that already intrudes into a yard counts as increasing the nonconformity, with narrow exceptions such as changing a flat roof to a pitched one. Second, Kirkland allows footprint growth outside the setback even when part of the house is inside it; growth within the setback needs a shoreline variance, except that a detached house built before December 1, 2006 can add up to 10 percent of its gross floor area there, no further waterward, with restoration, once in five years. Third, in Kirkland any alteration costing more than 50 percent of replacement cost requires nonconforming decks and patios in the setback, and an extra dock or covered moorage in the RSA or RMA zone, to be removed or brought into conformance.

The city detail sits in my guides to Mercer Island, Medina and Kirkland zoning.

Additions that trigger shoreline planting

Two cities set square footage triggers for planting along the shore:

• Mercer Island. New development of 500 square feet or more, any combination of added gross floor area, lot coverage or hardscape, requires native vegetation over 50 percent of a 20 foot vegetation area along the OHWM. At 1,000 square feet or more it becomes 75 percent. The total includes everything added in the five years before the application, and a shoreline vegetation plan must be approved (MICC 19.13).
• Issaquah, on Lake Sammamish. An expansion adding more than 500 square feet of impervious surface, counted over any five year period and including accessory structures, requires enhancing an equal area of the shoreline buffer with native vegetation. Impervious surface removed from inside the buffer and setback can be deducted, and if that brings the total under 500 square feet, no enhancement is required.

Kirkland uses restoration in a different way: the setback expansion allowance above requires restoring a portion of the setback to an equivalent or higher level of function, with a plan by a qualified professional. Seattle requires ecological restoration when nonconforming development outside the setback is substantially improved or replaced, if the director finds that removing the nonconformity would have improved ecological function.

Owners often resist planting because it sits between the house and the view. I place it early with the landscape architect, keep sight lines from the main rooms clear, and use any credit the code offers: in Issaquah, removing an old patio near the water reduces what you owe.

Height, views and going up

Going up on a tight waterfront lot runs into two height limits. State law bars a shoreline permit for a new or expanded structure more than 35 feet above average grade that would block the view of a substantial number of residences, except where the master program does not prohibit it and overriding considerations of the public interest are served (RCW 90.58.320). Then each city has its own number. On Mercer Island the shoreline limit matches the zoning limit and cannot exceed 35 feet above average building elevation. In Kirkland, where the shoreline chart and the zoning chart differ, the lower one applies.

A second story on a house inside the setback is where the nonconforming rules bite. Kirkland requires conformance when a roof is structurally altered on a structure that does not meet the setback (its pre-2006 allowance can permit an upper floor addition under the same conditions), and Mercer Island treats raising the part of a house inside a required yard as increasing the nonconformity. So the design question is often which part of the house can go up: the part outside the setback usually can, the part inside usually cannot. The lake house remodel ideas that work best here are the ones that keep the waterside rooms in place and add volume landward.

For how I approach the view side of the design, see lakefront home design on Lake Washington.

Docks, bulkheads, high water and moisture

A remodel of the house does not cover the dock or the bulkhead. Each has its own exemption or permit, and in-water work needs a Hydraulic Project Approval from the Washington Department of Fish and Wildlife (RCW 77.55.021) and often the U.S. Army Corps of Engineers. The detail, including dock dollar limits, is in the shoreline exemption guide. Keep them on a separate track, and check whether the remodel pulls them in, as a large one can in Kirkland.

The water also sets the elevations. Kirkland’s code ties the Lake Washington OHWM to a lake elevation of 18.5 feet (NAVD 88), and Issaquah allows 31.76 feet (NAVD 88) as the standard OHWM elevation on Lake Sammamish or a field determination by a qualified biologist. A survey that shows the OHWM, the setback line and your finished floor elevations is the first document I ask for. On the Sound, also ask the city whether the lot is in a mapped flood hazard area before you design lower floors.

A lake house can also have a crawlspace or basement close to the water table, and a remodel that opens walls is the time to fix drainage, vapor control and ventilation. See moisture management for Northwest renovations.

When keeping the house beats a rebuild

On a dry lot, a teardown and rebuild is often the cleaner answer for a tired house. On the water, the existing house may hold a position you could not get today. If it sits 15 feet from the water where the setback is now 25 feet or more, a new house usually has to move back to the current line, and the waterside rooms move with it.

That is why I price both options before design starts:

1. Map the nonconformity. Survey the OHWM and draw today’s setback on top of the existing house. Note which walls, rooms and decks are inside it.
2. Measure against your city’s limit. On Mercer Island, the wall length you would structurally alter over five years. In Medina, the wall framing removed. In Seattle, the cost of the work against market value. In Kirkland, which roofs and walls inside the setback you structurally alter, and the cost against replacement value.
3. Design to stay under it. Keep the waterside portion in place, rebuild and expand on the landward side, and phase nothing that would push the five year totals over.
4. Compare with a conforming rebuild. New construction runs $400 to $900 per square foot as a planning range, plus demolition typically $20,000 to $50,000, and in most cases the new house loses the closer position.

Sometimes the rebuild still wins, for example when the structure is poor or the nonconforming part is small, and two cities let a rebuild keep a shoreline position: Medina within the old footprint, and Mercer Island for a legally built structure within 25 feet of the OHWM, as long as the nonconformance does not increase. A good lake house remodel can look new from the water in the before and after photos while the code still treats it as the old house. The general version of this decision is in remodel or tear down and rebuild.

Timeline, fees and cost

Item	Planning figure	Notes
Design to permit submission	Typically 2 to 4 months	Survey, OHWM, existing conditions and the nonconforming analysis come first.
Remodel permit	About 2 to 3 months in Seattle	Plus shoreline review where needed; a new house in Seattle takes 6 to 10 months.
Whole house renovation	$300 to $550 per sq ft	Planning range.
Additions	$350 to $650 per sq ft	Planning range.
Design and permit fee	Fixed fee, about $10,000 to $200,000	Set by project budget and location.

Planning ranges from Piper Cole, not quotes. Shoreline, critical area and in-water reviews can add time.

I quote a fixed fee to design and permit, set by the project budget and location, and the remodels I take on start at a project budget of $750,000. Piper Cole designs houses and administers construction for the owner. Piper Cole does not build. Waterfront work in Seattle has its own design notes in waterfront home design in Seattle.

The first step is a feasibility check. The basic one is free and usually takes about a day: I look at the lot, the shoreline setback and where the existing house sits against it. An in-depth analysis, with the nonconforming math and remodel and rebuild options side by side, is $1,500 and takes 2 to 3 weeks.

Questions

Do shoreline rules apply to remodeling a waterfront house?

Yes. Within 200 feet of the ordinary high water mark, your city’s shoreline master program applies to a remodel or addition, including setbacks, vegetation requirements, height limits and nonconforming structure rules. A house built or remodeled for the owner’s own use, at or under 35 feet, is usually exempt from the shoreline substantial development permit, but not from the program itself.

Can I remodel a house that is closer to the lake than the current setback allows?

Usually yes, if it was legally built. Each city lets a nonconforming house be maintained and remodeled as long as the work does not increase the nonconformity, but each sets a limit. Mercer Island counts structurally altered exterior wall length (40 percent over five years for zoning nonconformities), Medina counts exterior wall framing removed (more than 60 percent), Seattle uses a cost test, and Kirkland requires a structurally altered roof or wall inside the setback to conform.

What is the 40 percent rule on Mercer Island?

Under MICC 19.01.050, a legally nonconforming house keeps its status through an alteration or addition only while no more than 40 percent of the length of its existing exterior walls is structurally altered, counted cumulatively over five years. A wall segment counts once any part of it is removed down to no structure. If the threshold is exceeded, the whole house must meet current code.

Can I add on to my waterfront house?

Usually, if the addition itself meets current rules. Expanding within the shoreline setback generally is not allowed without a shoreline variance, so additions go landward. Kirkland has a limited exception for detached houses built before December 1, 2006: footprint within the setback can grow up to 10 percent of existing gross floor area, no further waterward, with restoration of part of the setback, once in five years.

Does an addition on a waterfront lot require shoreline planting?

Often. On Mercer Island, adding 500 square feet or more of floor area, lot coverage or hardscape, counting the prior five years, requires native vegetation over 50 percent of a 20 foot area along the water, and 75 percent at 1,000 square feet. In Issaquah, adding more than 500 square feet of impervious surface in five years requires enhancing an equal area of the Lake Sammamish buffer.

Can I add a second story to a lake house inside the shoreline setback?

It depends on the city and the part of the house. Kirkland requires a roof or wall that does not meet the shoreline setback or height to be brought into conformance when it is structurally altered, and Mercer Island treats raising the part of a house inside a required yard as increasing the nonconformity. Going up on the landward part of the house is usually the easier path.

Is it better to remodel or rebuild a waterfront house?

If the existing house sits closer to the water than today’s setback allows, a remodel that stays within your city’s nonconforming limits can keep that position, while a new house usually must meet the current setback (Medina and Mercer Island have limited rebuild exceptions). Compare both, using planning ranges of $300 to $550 per square foot for whole house renovation and $400 to $900 per square foot for new construction.

How long does a waterfront remodel take to permit?

Design to permit submission typically takes 2 to 4 months. In Seattle a remodel permit can be obtained in about 2 to 3 months, plus shoreline review where it applies. Critical area review, a shoreline variance or in-water permits for a dock or bulkhead add time.

Does a remodel permit cover my dock or bulkhead?

No. Docks and bulkheads have their own shoreline exemptions or permits and usually need a Hydraulic Project Approval from the Washington Department of Fish and Wildlife, and often a U.S. Army Corps of Engineers permit. In Kirkland, a large remodel of the house can also require an extra dock or covered moorage to be removed or brought into conformance.