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Structural engineering
Structural engineer for a home remodel in Seattle and on the Eastside
Which remodel moves need a structural engineer, what the engineer produces, who may stamp the drawings in Washington, and where the engineer fits in the order of work on a $750,000 or larger project.
On this page
- Which remodel moves bring in an engineer
- What the residential code says about engineered design
- Who may stamp structural drawings in Washington
- What Seattle and the Eastside cities publish
- What the engineer delivers
- Who hires the engineer, and the order of work
- A 1960s rambler and split-level, move by move
- The free check and the schedule
- Questions
Key takeaways
- A remodel needs a structural engineer when it changes how weight reaches the ground or how the house resists earthquake or wind: a bearing wall, a new story, a wide opening, new footings, a basement dig out, a slope.
- The residential code sends anything outside its prescriptive limits to engineered design (R301.1.3). SDCI’s Tip 303A says projects that miss its listed requirements need an alternate design with calculations from a licensed Washington structural engineer.
- State law does not restrict who designs a residential building of up to four units (RCW 18.08.410). Seattle’s code asks for an architect or structural engineer but lets the building official authorize detached houses without one (R105.6.1).
- The engineer’s sheets go into the permit set, inside the 2 to 4 months it typically takes me to design and submit for permit. I give no engineer fee; ask for a written proposal.
Short answer: you need a structural engineer when a remodel changes the path a load takes to the ground, or the way the house resists an earthquake or wind. Opening a bearing wall, adding a story, cutting a wide opening in an exterior wall, changing a footing, digging out a basement and building on a slope qualify. A partition that carries nothing, and new finishes and fixtures, do not.
Who this is for: an owner planning a remodel of $750,000 or more. Piper Cole designs and administers construction and does not build. I read the 2021 Seattle Residential Code (SRC), SDCI Tips 101, 303A and 316, chapters 18.08 and 18.43 RCW and the city checklists below on October 13, 2026. Confirm with your city.
Which remodel moves bring in an engineer
I sort moves by what they do to the load path, the route weight takes from roof through walls and floors to the ground. If a move interrupts it, an engineer designs what replaces it.
| Move | Why it is structural | What the sources say |
|---|---|---|
| Remove or open a bearing wall | Its roof or floor load goes into a beam, posts and new footings. | Seattle’s minor-work exemption excludes removing any loadbearing support (SRC R105.2). Bellevue lists beams and headers among elements outside R301 that need engineering. |
| Add a second story | Old footings, walls and bracing carry weight they were not sized for. | The footing table sizes footings by stories and soil (R403.1(1)). In category D2, a wood-framed building over two stories has its wind and seismic loads designed by accepted engineering practice (R301.2.2.7). |
| Cut a wide opening in an exterior wall | It needs a header and can remove bracing length. | Parts that miss the wall bracing rules are designed under R301.1 (R602.10). Seattle’s interpretation of R105.6 says buildings with steel moment frames must be designed by a licensed structural engineer. |
| Change footings, or dig out a basement | New posts need footings, and lowering a floor changes what bears on the soil. | Tip 303A asks for an alternate design with calculations from a licensed Washington structural engineer where a project misses its listed requirements. My basement guide has the detail. |
| Vault a ceiling or reframe the roof | Removing ceiling joists lets the walls spread. | Framing beyond the limits of section R301 is engineered (R301.1.3). |
| Offset floors, big floor openings, tall cripple walls on a slope | Irregular framing is outside the code’s seismic provisions. | In Seattle’s D2, these are irregular, and engineered unless an exception applies (R301.2.2.6). |
In Seattle, a substantial alteration (the building official decides, R107.5.1.1) must meet R301.1.3 or the anchor bolt and bracing sections (R403.1.6, R602.10, R602.11), unless the official approves strengthening the foundation and cripple walls instead. The official may also require testing of existing materials (R107.5.1.2). The rambler guide explains the test.
What the residential code says about engineered design
Washington adopts the 2021 International Residential Code, effective March 15, 2024 (WAC 51-51-008). Seattle enforces its own Seattle Residential Code. The key sentence is R301.1.3: structural elements that exceed the limits of section R301 or do not conform to the code are designed under accepted engineering practice. The state amends R301.2, R301.2.2.10 and R301.5, and leaves R301.1.3 alone (WAC 51-51-0301). The state has proposed a 2024 edition effective May 3, 2027 (WSR 26-10-071), so section numbers may change.
The prescriptive path is a set of tables: header spans (R602.7), wall bracing (R602.10), footings by stories and soil (R403.1). Stay inside them and plans need no calculations. SDCI’s Tip 101 (June 30, 2026) says the code typically does not require Washington-licensed designers for single-family plans, that complex structural designs for alterations are developed by an engineer, and that the prescriptive route is cumbersome except for very simple structures.
Design loads come from each city’s table, so they differ. Seattle’s Table R301.2 lists 20 psf ground snow, 98 mph wind and seismic category D2. Redmond’s design sheet lists 15 psf, 110 mph and D2 for residential. I give no values for other cities, and your engineer confirms the loads with your city. Bellevue publishes a snow load policy for higher elevations; ask whether it applies to your lot. On a slope, a light-frame house is engineered from the lowest framed floor down when the grade averages over 1 in 5 along a side, cripple walls or posts exceed 7 feet and under half the area below that floor is living space, unless that floor sits on concrete or masonry walls on all sides but the downhill one (R301.2.2.6).
Who may stamp structural drawings in Washington
None of the sources below says you must hire an architect for a house. Seattle’s default is an architect or a structural engineer, with an exception the building official may grant.
- Engineers. Practicing or offering engineering requires registration under chapter 18.43 RCW. A registrant’s plans, specifications and reports are signed, dated and stamped, and stamping after registration lapses is unlawful (RCW 18.43.070).
- Structural engineers. Registration as a structural engineer is required for significant structures (RCW 18.43.040(2)): hazardous facilities, certain essential facilities, structures over 100 feet, occupied buildings of five or more stories, large bridges and places where over 300 people gather (RCW 18.43.020(10)). None describes an ordinary house.
- Architects. Practicing architecture includes design of any structure (RCW 18.08.320), and the chapter does not prevent any person from design work on a residential building of up to four dwelling units (RCW 18.08.410).
- Seattle. Construction documents are prepared by or under an architect or structural engineer licensed in Washington, who seals each sheet in their scope. When the building official authorizes it, detached one- and two-family dwellings need neither (SRC R105.6.1, exception 1.1). Buildings with steel moment frames are outside that exception (interpretation of R105.6).
Chapter 18.43 RCW does not prevent the practice of any other legally recognized profession (RCW 18.43.130), and RCW 18.08.410(1) leaves engineering under chapter 18.43 alone, so where the line between architect and engineer falls on a given job is a question for the state boards. In practice the stamp follows the calculations. Redmond requires stamped, signed calculations from a Washington State design professional when calculations are required, and Kirkland requires a stamp where a licensed professional prepared the sheets. Ask any architect, including me, whether an engineer’s calculation sits behind every beam that carries a floor or roof. No code in these sources requires it for a detached house. Confirm the engineer’s Washington registration with the state board, whose roster is public (RCW 18.43.035).
What Seattle and the Eastside cities publish
For fees and steps, see my guides to Bellevue, Kirkland and Redmond and the Seattle permit fee guide.
| City | What its published document says | Document |
|---|---|---|
| Seattle | Major renovations, alterations and additions go to plan review, and structural is one of the reviews. Plans show the foundation and framing, including affected existing framing. Tip 303A says SDCI generally does not require a design professional’s stamp for detached one- and two-family dwellings except complex structures, subject to its approval. The quick field-inspection permit stops at bearing-wall openings carrying more than one story plus roof and at beam spans over 14 feet (30 with a manufactured truss). | SDCI Tips 101, 303A, 316; SRC R105.6 |
| Bellevue | Structural plans show foundation, framing and lateral system with shear wall and hold-down schedules. Single-family structures designed under the residential code are exempt from the stamped engineered plans requirement. Elements outside R301 need engineering: beams and headers, shear walls, basement walls, retaining walls over 4 feet. | Bellevue structural plan and calculations pages |
| Kirkland | Structural drawings and any structural calculations that were done must be submitted, and a licensed design professional’s sheets must be stamped. A geotechnical report is required in soft soils, landslide or seismic hazard areas, or where the foundation is deep or unusual. | Kirkland Single Family/Duplex Permit Checklist (PDF) |
| Redmond | Calculations are not required when the design comes straight from the code. When required, a Washington State design professional stamps and signs them. | Redmond Residential Application Packet (09/2026) |
| Sammamish | The residential addition checklist lists structural calculations among required items. | Sammamish addition checklist (version 2022.10 AB) |
I did not read the checklists for Mercer Island, Issaquah, Medina, Clyde Hill, Yarrow Point or Hunts Point for this page; ask those departments.
What the engineer delivers
- A look at what is there. The direction, size, spacing and span of the existing framing and the location and size of openings, which SDCI’s quick-permit guidance (Tip 316) asks applicants to show. In a 1960s house that means the attic and crawl space, and sometimes opening a ceiling.
- Calculations. Gravity work sizes beams, headers, posts and footings. Lateral work designs the shear walls, hold-downs and connections that resist wind and earthquake.
- Stamped structural sheets. Notes with design loads, foundation and framing plans, sections and details (SRC R105.6.2 and R105.6.4).
- Answers to the reviewer. The engineer revises or explains the sheets after a correction letter.
- Site visits and field reports, if the scope says so. Washington’s definition of engineering practice includes supervising construction to assure compliance with the design (RCW 18.43.020(6)), so visits are a line in the engineer’s agreement and do not come automatically. The city’s inspections are separate. If the work differs from the approved plans, Seattle requires a revision (Tip 101).
Who hires the engineer, and the order of work
The statutes I read do not decide it. The architect can engage the engineer as a consultant, or you can hire the engineer directly. What matters is one coordinator: Seattle’s code lets the building official require the owner to designate a registered design professional in responsible charge, who coordinates the documents others prepare so they fit the building’s design (R105.6.1.1).
On a Piper Cole project I coordinate the engineer, fold the engineer’s sheets into one permit set and administer construction. I do not build, so a builder you hire does the work. Who signs the engineer’s agreement and who pays belong in writing before engineering starts. Ask every architect on your list, including me. I put no price on an engineer here; a written proposal listing the deliverables is how you compare. The order I would ask any architect to confirm, including me:
- Look and measure. Survey, original drawings if any, framing and foundation.
- Design with the structure in mind.
- Engineer sizes and details the moves that need it.
- One permit set, architectural and structural sheets together, then submit.
- Respond to corrections, with the engineer on structural comments.
- Build. Construction administration by the architect; engineer visits only if the agreement includes them.
A 1960s rambler and split-level, move by move
These rows match my rambler guide and split-level guide.
| Move | Engineer? | Why |
|---|---|---|
| Rambler: open the wall between kitchen and living room | Yes | If the ceiling joists or rafters land on it, a beam, posts and new footings replace it. |
| Rambler: vault the ceilings | Yes | Ceiling joists tie the walls together. Removing them calls for a ridge beam or ties, and trusses are replaced or the roof reframed. |
| Rambler: add a second story | Yes, before design | The footing table asks for 15 inches under two stories where it asks for 12 under one, on 1,500 pound soil over a crawl space. Walls and bracing need checking too. |
| Rambler: move a partition that carries nothing | Usually no | Confirm the framing direction in the attic and crawl space first. A wall near the middle, running across the joists, is the one to question. |
| Either: new finishes, cabinets, fixtures, windows in existing openings | No | The load path does not change. Permit and energy code rules still apply. |
| Split-level: change how the half-levels stack | Yes | A floor level offset is irregular unless the framing sits on continuous perimeter foundations or the floors are lapped or tied as the code requires. |
| Split-level: lower level on a slope with tall cripple walls | Yes, if all three hillside conditions apply | Slope, wall height and the living-space share decide it (R301.2.2.6). |
The free check and the schedule
The free feasibility check is very quick, about a day. A day cannot tell you what a wall carries, because that takes someone who has seen the framing. Ask whoever runs your check, including me, which of your moves are likely to need an engineer, so that line is in the budget conversation from the start. The in-depth analysis is $1,500 and takes 2 to 3 weeks.
Structural sheets are part of the permit submission, so engineering falls inside design to permit submission, which typically takes me 2 to 4 months. After submission, a Seattle remodel permit can be obtained in about 2 to 3 months. SDCI’s Tip 101 puts initial review of single-family additions and alterations at 2 to 4 weeks, which can double in heavy volume, and says to plan for multiple rounds of review. Eastside cities run their own queues. I found no published duration for engineering alone, so I give none.
Four things add time: access to open a ceiling or the crawl space, a geotechnical report (Kirkland requires one in several conditions), plan changes after members are sized, and a field condition that differs from the drawing, which means a revision to the approved plans.
I have been an architect since 1996, an AIA member since 1992 and an NCARB member since 1996, and I take on 20 to 30 projects a year. The Carr residence was featured in Above The Lake and Lux magazines. For budget, see planning a million dollar remodel; for how I work in Seattle, hiring a whole house remodel architect.
Before you commit to a plan
Find out what your house can carry
Send me the address, a few photos and the move you have in mind. The free feasibility check takes about a day, and the in-depth analysis is $1,500 and takes 2 to 3 weeks.