Short answer: a second story addition and a whole house remodel on the same house is one project with one budget, and three things decide it before any drawing: whether the existing structure can carry a new floor, which parts of the old house the city then pulls under current code, and whether the lot’s floor area, height and yard rules leave room for the floor you want. At this site’s planning ranges, 1,000 square feet of addition plus a 2,000 square foot remodel starts at $950,000, above $750,000, my smallest project. The first basic feasibility check with me is free and very quick, usually about a day. Send me the address and what you are considering, and I will reply to you personally. An in depth analysis is $1,500 and takes 2 to 3 weeks. Piper Cole Architects designs and administers construction and does not build. My firm is based in Kirkland.
Key takeaways
- At planning ranges, 1,000 square feet of addition plus 2,000 square feet of remodel is $950,000 to $1,750,000 of construction, with design fees, permits, tax and contingency on top.
- A new floor tests the old house. In the 2021 Seattle Residential Code, the new work and the existing building together must meet the structural requirements for new construction, unless an engineering evaluation shows the existing structure is sufficient (R4405.3).
- A second floor adds floor area and no footprint. In Seattle’s Neighborhood Residential zones, as of October 2026, a single house with no accessory unit on a 5,500 square foot lot is capped at 3,300 square feet of floor area, and that cap can bind before coverage or yards do.
- Cities draw the line for a bigger project in different places. Bellevue sorts permits at 3,000 square feet of new and/or replaced floor area and does not say how a mixed project is counted.
- The first check is free and usually takes about a day. The in depth analysis is $1,500 and takes 2 to 3 weeks.
An addition and a whole house remodel are one project
My pages on second story addition cost, Eastside second story additions, Kirkland additions and Bellevue second story additions are about the addition on its own. This page is for the owner whose scope is the new floor and a remodel of the house under it. The floor above changes the structure below, and the remodel opens walls the addition has already touched.
Washington law does not require an architect for a house (RCW 18.08.410(5)), so hiring me is your call. This page takes four questions in order: structure, then the city’s pull on the old house, then the lot’s limits, then the budget.
Request your free feasibility check
Send me the address and what you are considering: the new floor, the rooms, and what else in the house you want to remodel. I will reply to you personally.
Prefer to talk? Call 425 753 6452 or message David on WhatsApp.
Free feasibility check
Planning a custom home or a remodel of $750,000 or more?
Send me the address and a few lines about what you want. The first feasibility check is free and usually takes about a day.
Worked example: what the two add up to
Take an addition of 1,000 square feet and a remodel of the 2,000 square foot house under it. I use this site’s planning ranges: additions $350 to $650 per square foot and whole house renovation $300 to $550 per square foot. They are planning ranges, not a quote. Plan design fees, permits, sales tax and contingency on top, and treat a builder’s bid on finished drawings as the real number.
| Piece | Planning range | Arithmetic | Result |
|---|---|---|---|
| Addition, 1,000 sq ft | $350 to $650 per sq ft | 1,000 x 350 and 1,000 x 650 | $350,000 to $650,000 |
| Remodel, 2,000 sq ft | $300 to $550 per sq ft | 2,000 x 300 and 2,000 x 550 | $600,000 to $1,100,000 |
| Whole project | Sum of the two | 350,000 + 600,000 and 650,000 + 1,100,000 | $950,000 to $1,750,000 |
A smaller mix still straddles my minimum: 500 square feet of addition plus 1,500 of remodel is 500 x 350 + 1,500 x 300 = $625,000 at the bottom and 500 x 650 + 1,500 x 550 = $1,150,000 at the top. See the million dollar remodel guide and remodel, addition or new build.
What the existing house has to carry
A second floor adds weight to the walls, footings and the frame that resists earthquake and wind. Seattle’s permit department says any structural impacts of an addition or remodel must be accounted for in the design and permit submittal, and that with a second story addition the existing house may need structural upgrades (SDCI). The residential code is specific.
- Vertical additions. Where new construction adds a story to any part of the existing building, the new construction and the existing building together must meet all the structural requirements for new construction. If the two are evaluated together under accepted engineering practice and shown sufficient for the combined loads, no structural alterations are required (R4405.3, chapter 44).
- Increased loads. The existing components that carry added load, the foundation included, must be shown to comply or be altered (R4404.4.2). Wind load counts as increased when an exterior elevation grows by more than 5 percent (R4404.4.2.4). If a 40 foot wall 9 feet high (360 square feet) gains a second 9 foot story, it becomes 720, up 100 percent. The heights are my assumption.
The answer sits in footings and framing you cannot see until someone checks, and a structural engineer makes the call. See the structural engineer guide and the guide to existing conditions and as-built drawings. This is Seattle’s text. Each Eastside city publishes the version it enforces, so ask for yours.
When an addition pulls the rest of the house in
SDCI says you do not need to upgrade the parts of your house that are not being remodeled to current codes (SDCI). In an addition plus a whole house remodel most of the house is being remodeled, so that sentence protects less than it first appears.
| Rule | What the source says | What it means here |
|---|---|---|
| Substantial alteration, Seattle Residential Code R107.5.1 | The building official may 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. The house then meets current rules for escape openings, egress, smoke and carbon monoxide alarms and dwelling unit separation, plus the seismic provisions, which the official may accept as strengthened foundations and cripple walls (R107.5.1.2). | A new floor plus a whole house remodel can fit this wording. The official decides, so the cost belongs in the budget from day one. |
| Nonconformity, R4404.3 | The work shall not increase the extent of noncompliance or create nonconformity that did not exist. | The new floor cannot add a code problem to the old house. |
| Energy code, WAC 51-11R | An addition meets the code as new construction without requiring the unaltered part to comply (R502.1). Additions of 150 square feet or less need not comply with R406 (R502.1.1). Space that becomes conditioned must fully comply (R502.2). Existing cavities exposed in an alteration may be filled with insulation, at least R-15 in 2 x 4 walls and R-21 in 2 x 6 walls (R503.1.1). | The remodel opens the walls and the new floor is built to the new standard. See my energy code guide. |
| Bellevue, nonconforming buildings | The city’s form says remodels or expansions of nonconforming buildings above a percentage of replacement value, or a size, may require the site to come into partial or full compliance (LUC 20.20.560). The form is dated October 19, 2018. | Whether a large project crosses that line depends on whether the building is nonconforming and on the city’s current numbers, so ask the city before design depends on it. |
| Other Eastside cities | Each city sets its own test and publishes its own code, so ask for the current text. | See when a remodel counts as a new house. |
Sources, all read October 31, 2026: chapter 1 and chapter 44 of the 2021 Seattle Residential Code, the residential Washington State Energy Code (effective March 15, 2024) and Bellevue’s value of improvements form.
Second story addition and remodel: floor area, height and yards
A second floor leaves the footprint alone, so it adds no lot coverage. It adds floor area and height, and those can bind. I work the example in Seattle, whose Neighborhood Residential rules took effect on January 21, 2026 (city One Seattle Plan page). The same page says the changes remain in effect while the city prepares its new analysis, so confirm the rules on the day you apply. The numbers come from Ordinance 127376 and the city’s January 2026 summary.
| Step | What the code says | Arithmetic | Result |
|---|---|---|---|
| Lot | Interior lot, Neighborhood Residential zone, one dwelling unit and no accessory unit, no critical area or shoreline | 50 x 110 | 5,500 sq ft |
| Floor area cap | Ratio of 0.6 where density is below one unit per 4,000 sq ft (SMC 23.44.050, Table A) | 5,500 x 0.6 | 3,300 sq ft |
| Lot coverage | 50 percent (SMC 23.44.080.A) | 5,500 x 0.50 | 2,750 sq ft of footprint |
| Height | 32 feet; a pitched roof ridge may rise 5 feet more if the roof above the limit is 4:12 or steeper (SMC 23.44.070.A.1 and B.1); 42 feet where the lot keeps a Tier 1 or Tier 2 tree or reaches a tree point score with trees giving 10 percent canopy at maturity (A.2.d) | 32 + 5 | 37 feet at the ridge |
| Front and rear yards | 15 feet each; the rear applies where the lot does not abut an alley (SMC 23.44.090, Table A) | 110 to 15, 15 | 80 feet of depth |
Assume the existing house is one story, 2,000 square feet, garage included, with no basement. I count the whole floor because the exemptions in SMC 23.44.050.C list underground floor area and portions of a story no more than 4 feet above grade, and no garage. Confirm with SDCI how it counts yours.
Plan 1. A 1,000 square foot second floor. Floor area is 2,000 + 1,000 = 3,000, which is 300 under 3,300. Footprint stays 2,000, under 2,750. It fits.
Plan 2. Plan 1 plus a 500 square foot rear addition. Floor area is 3,000 + 500 = 3,500, which is 200 over. Footprint is 2,500, still under 2,750. Floor area decides Plan 2, and no yard or coverage number warns of it. The rear addition can be 3,300 to 3,000 = 300 square feet at most.
The wall in the side yard. Side yards are 5 feet on average and 3 feet at minimum (SMC 23.44.090, Table A). An addition to an existing dwelling may extend into a required side setback only if the nonconforming part is at least 60 percent of that facade’s width, the addition stays at least 3 feet from the side lot line, and it comes no closer than the closest part of the existing house (SMC 23.44.090.J). On a 40 foot facade, a nonconforming wall along 28 feet is 28 / 40 = 70 percent and the 60 percent test is met. Along 20 feet it is 20 / 40 = 50 percent, and under this rule the new floor must stay out of the required yard. A wall 2.5 feet from the line fails the 3 foot condition. How the city measures the 5 foot average is a question for SDCI.
Other cities use other numbers. See my guides to Seattle, Bellevue, Kirkland and Mercer Island zoning, and the Seattle FAR explainer.
One permit set or two, and living at home
Seattle. SDCI’s permit page, Construction Permit, Addition or Alteration, covers additions and alterations. An addition changes the outside, such as adding floor area, and a remodel changes the interior. Large work such as an additional story needs a regular building permit instead of the quicker subject-to-field-inspection permit (SDCI permit page). The page does not say how a project that is both is handled, so ask SDCI. It tries to finish initial review of complex permits in eight weeks, and the time to a final permit depends on corrections. This page gives no permit timeline for a project with a new floor, because the city’s own pages give only the review goal.
Bellevue. The city sorts permits by what changes (permit index):
| Permit | What the city says it covers | What it asks for |
|---|---|---|
| BR, addition under 3,000 sq ft | Adding on to an existing house, new or replaced living space (city page) | Plans, boundary and topographic survey, structural and lateral calculations, energy code sheet, value of improvements form |
| BS, large addition | An addition greater than 3,000 square feet of new and/or replaced floor area (city page) | Adds an arborist report, civil plans and a shoring plan; one bookmarked PDF set |
If replaced area counts square foot for square foot, a 1,000 square foot addition that replaces 2,000 square feet of floor comes to 3,000, which is not greater than 3,000, and at 3,001 it is. The BR page says less than 3,000 and the BS page says greater than 3,000, so exactly 3,000 sits between them. The city’s pages do not say how replaced floor area is counted, so ask before the design depends on it.
Phasing. Two permits, the addition now and the remodel later, may not get you under a city’s line: Bellevue’s value of improvements form asks for the value of other improvements completed within the last 12 months, and two permits mean two review cycles. Living at home. Whether you can stay is a question for the phasing plan and the builder. See remodeling while living at home and how long a whole house remodel takes.
How it works with me
Send me the address and what you are considering. I will reply to you personally. The first check is a basic feasibility study, free and very quick, usually about a day. The in depth analysis goes further, takes 2 to 3 weeks and costs $1,500. Only the city can approve a project.
- Free first check. Usually about a day.
- In depth analysis, if you want it. $1,500, 2 to 3 weeks.
- Design to permit submission. Typically 2 to 4 months, for a fixed fee set by project budget and location, about $10,000 to $200,000 depending on scope.
- Construction. Piper Cole designs and administers construction and does not build.
I have been an architect since 1996, an AIA member since 1992 and an NCARB member since 1996. The Carr residence was featured in Above The Lake and Lux magazines.
Before you design the new floor
Send me the address
Use the form above, call or message me on WhatsApp. The first check is free and usually takes about a day, and the in depth analysis is $1,500 and takes 2 to 3 weeks.
Questions
What is the difference between a second story addition and a whole house remodel, and can they be one project?
An addition adds floor area or height, and a remodel changes the interior and systems of the existing house. Yes, they can be one project, and an owner can do both, because a new floor opens the walls below. At this site’s planning ranges, 1,000 square feet of addition plus 2,000 square feet of remodel comes to $950,000 to $1,750,000 of construction. Send me the address and what you are considering and I will reply to you personally.
How much does a second story addition and remodel cost?
As planning ranges only, additions run $350 to $650 per square foot and whole house renovation $300 to $550 per square foot. For 1,000 square feet of addition plus 2,000 of remodel that is $350,000 to $650,000 plus $600,000 to $1,100,000, a total of $950,000 to $1,750,000, with design fees, permits, sales tax and contingency on top. A builder’s bid on finished drawings is the real number.
Does a second story addition force the whole house up to current code?
Not by one rule. Seattle’s permit department says existing parts not being remodeled need not be upgraded, but structural impacts must be accounted for. In an addition plus a whole house remodel, the building official may treat the work as a substantial alteration under R107.5.1 of the 2021 Seattle Residential Code, which brings current exit, alarm and seismic requirements. Altered parts must also meet the energy code. Eastside cities set their own tests.
Can my existing foundation and walls carry a second story?
It depends on what is there, and an engineer decides. In the 2021 Seattle Residential Code, a vertical addition and the existing building together must meet the structural requirements for new construction, unless an engineering evaluation shows the existing structure sufficient for the combined loads (R4405.3). Existing components that carry added load, the foundation included, must be shown to comply or be altered (R4404.4.2).
How tall can a second story be in Seattle?
In Seattle’s Neighborhood Residential zones, as of October 2026, the height limit is 32 feet, and the ridge of a pitched roof may rise 5 feet higher if the roof above the limit is pitched at 4:12 or steeper. The limit is 42 feet where tree conditions are met (SMC 23.44.070). Floor area can be the tighter limit: 0.6 times the lot area for a single house with no accessory unit, so 3,300 square feet on a 5,500 square foot lot. Confirm with SDCI before you rely on a number.
Can I build a second floor over a wall that is inside the side yard?
Sometimes. Seattle lets an addition to an existing dwelling extend into a required side setback if the nonconforming part is at least 60 percent of the facade width, the addition stays at least 3 feet from the side lot line, and it is no closer than the closest part of the existing house (SMC 23.44.090.J). Other cities have their own tests, so the answer depends on the city and on a survey.
Do I need one permit or two for an addition and a remodel?
It depends on the city. Seattle’s permit page covers additions and alterations together, and large work such as an additional story needs a regular building permit. Bellevue sorts by what changes: an addition over 3,000 square feet of new and/or replaced floor area is a different permit from a smaller addition. The city pages do not say how a mixed project is counted, so ask the city before design depends on it.
Can we live in the house during an addition and whole house remodel?
It depends on the phasing plan and the builder. With the roof off for a second story the house is open to weather while framing and roofing go on, so budget for renting and storage until the builder says otherwise. A phased project that keeps one wing livable has to be designed in from the start and priced by the builder.
Does Washington require an architect for an addition to my house?
No. RCW 18.08.410(5) says the architect licensing chapter does not prevent any person from doing design work, including construction contract documents and administering the construction contract, for a residential building of up to four dwelling units, regardless of size. I can design the project and administer construction, and Piper Cole does not build.
