Second-story addition in Seattle: SDCI permits, cost, timeline

A Seattle second-story addition is typically a 14 to 24 month project — about 30 steps across 7 phases, from feasibility through final inspection. The classic case is a one-story Craftsman bungalow in Ballard, Wallingford, Ravenna, Mount Baker, or West Seattle getting a pop-up. The Seattle Department of Construction and Inspections (SDCI) runs the permit on the Addition/Alteration track rather than as a new build, which means substantial-alteration triggers (CAM 314), pre-1978 lead-paint rules, pre-1980 asbestos rules, and an existing foundation that may or may not carry the new load. Turnkey budgets land in the $400,000–$800,000 range for envelope plus light system upgrades, and most families have to move out for 6–12 months. This is the workflow most owners run through, in the order most builders recommend. Click any step on the project map to read the detail. Steps stacked side-by-side run in parallel.

1. Phase 0

   Feasibility

   Before you pay anyone, confirm the addition is actually allowed and the house is actually a candidate. Four free or near-free checks that take 2–4 weeks and tell you whether to keep going.

   2-4 weeks·Free to ~$600 (test kits)·4 steps
   1. 2 in parallel
      0.1Confirm zoning, height limit, and FAR for your lotLook up your lot in SDCI's GIS portal and read the height, lot coverage, and FAR rules for the zone — that's how you find out whether a second story actually fits before you spend a dollar.Homeowner1-2 days · Free0.2Pull SDCI permit and site history for your addressRun your address through SDCI's permit research tool to find every prior permit, code violation, or open notice on the property. Free, takes about 15 minutes, surfaces things that would otherwise blow up the project mid-build.Homeowner15 minutes · Free
   2. 0.3Walk the house with an experienced second-story builderGet a builder who has actually done a Seattle pop-up to walk through the house with you for an hour. They'll tell you in 60 minutes what would otherwise take you four months of design fees to discover.Homeowner, General contractor1-2 hours · Free (most do free walk-throughs)
   3. 0.4Lead and asbestos screening testIf the house is pre-1978, hire a certified inspector for a $300–$600 screen for lead paint and asbestos in suspect materials. Knowing what's there is what lets you scope abatement properly.Homeowner1-2 weeks · $300-$600
2. Phase 1

   Site and existing conditions

   Three or four documents that describe what you've actually got: a measured survey of the lot, a measured drawing of the existing house, a structural read on the foundation, and (sometimes) a geotech report. The designer needs all of this before they can draw anything.

   4-8 weeks·$3,500-$15,000·4 steps
   1. 2 in parallel
      1.1Order a boundary and topographic surveyHire a licensed land surveyor to set the property corners, shoot the topography, and locate trees and existing improvements. The designer can't draw setbacks or coverage without it.Surveyor2-4 weeks · $1,500-$3,5001.2Measured drawings of the existing houseThe designer (or a separate measurer) measures every wall, window, door, and floor-to-ceiling dimension of the existing house. The new design lays on top of these drawings — they have to be accurate.Designer1-2 weeks · $1,500-$4,000
   2. 2 in parallel
      1.3Foundation Assessment for a Seattle Second Story AdditionA licensed structural engineer rates your existing foundation — adequate, needs retrofit ($15K–$60K), or lift-and-replace — in 1–2 weeks for $800–$2,500.Structural eng.1-2 weeks · $800-$2,5001.4Geotech report (only if site triggers it)Most flat-lot additions don't need a geotech report. If you're on a slope, in an Environmentally Critical Area, or the structural engineer flags soil questions, this is when you order one.Geotech eng.2-4 weeks · $3,500-$8,000 if required, $0 otherwise
3. Phase 2

   Design and engineering

   Pick a designer, make the lift-vs-retrofit call, get to a permit-ready stamped set. This is where 4–8 months of the schedule lives, and it's the highest-leverage spend on the whole project.

   4-8 months·$25,000-$60,000·5 steps
   1. 2.1Hire a designer or architect with Seattle older-home addition experiencePick a designer who has done at least three Seattle second-story additions in the last few years. Their muscle memory for SDCI's review pattern and the realities of older Seattle houses is what you're paying for.Homeowner, Designer, Architect2-3 weeks (selection) + ongoing through Phase 3 · $25,000-$60,000 for full design + permit support
   2. 2.2Make the lift-vs-retrofit decisionWith the foundation assessment in hand, you and the designer make the call: build on the existing foundation (with retrofits), lift the house and build a new foundation underneath, or lift and add a new ground floor too. This decision shapes everything downstream.Homeowner, Designer, Structural eng.1-2 weeks · Free (decision) — drives $20K-$150K+ downstream
   3. 2.3Schematic design + neighborhood-fit reviewThe designer produces three to five floor-plan and massing options. You pick one, refine it together, and end the step with a single concept that fits the lot, the neighborhood, and your budget.Designer, Architect, Homeowner4-8 weeks · Included in design fee
   4. 2 in parallel
      2.4Full structural engineering for the addition + retrofitThe structural engineer designs the new framing, the load path through the existing house, and the foundation retrofit (or new foundation). The designer's drawings get the engineer's stamp before submittal.Structural eng.4-6 weeks · $5,000-$12,0002.5Energy code compliance plan (WSEC alterations)The designer documents how the project meets the Seattle Energy Code's alteration requirements — different rules than new construction, and friendlier than most homeowners expect.Designer, Energy consultant1-2 weeks · Included in design fee, or $500-$1,500 if outsourced
4. Phase 3

   Permits and approvals

   Submit to SDCI, file the sub-permits, navigate any tree review, and work through the correction-letter loops. Three to seven months from intake to issuance is the honest range. The single longest unbroken stretch of the project.

   3-7 months·$8,000-$25,000 in fees·4 steps
   1. 3.1Submit the SDCI Addition/Alteration permitYour designer submits the permit set through the Seattle Services Portal. SDCI charges 75% of the permit fee at intake, opens the file, and assigns reviewers across zoning, structural, energy, and (if applicable) ECA.Designer, SDCI, Homeowner1-2 weeks (intake) + 4-8 weeks for first review · $5,000-$15,000 (75% at intake; based on project value)
   2. 2 in parallel
      3.2File electrical, plumbing, and mechanical sub-permitsYour electrician, plumber, and HVAC sub each pull their own permits — separate from the building permit. They can file as soon as the building permit is in review; no need to wait for issuance.Electrician, Plumber, HVAC contractor, SDCI, King County1-3 weeks per sub-permit, in parallel · $300-$800 per sub-permit, $1,500-$3,000 total3.3SDCI tree review (only if a regulated tree is in play)If your survey shows a tier 1 or tier 2 regulated tree near the work area, SDCI tree review applies. If not — and most additions don't have one — you skip this step entirely.Arborist, SDCI2-6 weeks if triggered, 0 otherwise · $1,500-$3,500 for arborist report if needed
   3. 3.4Respond to SDCI correction letters (1-3 cycles typical)Your designer turns SDCI's review comments into revised drawings and a response letter. Each cycle is 4-6 weeks. Most additions clear in 1-3 cycles; complex substantial-alteration projects can run longer.Designer, Architect, SDCI4-6 weeks per cycle, 1-3 cycles typical · Included in design fee; SDCI hourly $292/hr if review goes long
5. Phase 4

   Bid and contract

   Send the permit-ready set to three to five GCs who've actually finished Seattle additions on older houses. Verify them, negotiate the contract, sign it, bind insurance, and figure out where the family lives during the build.

   6-10 weeks·$2,000-$8,000 (insurance + attorney + temporary housing setup)·4 steps
   1. 4.1Solicit bids from 3-5 Seattle older-home addition GCsSend your permit-ready plans to three to five GCs who've actually built second-story additions on older Seattle houses, and ask them all to bid the same scope so you can compare apples to apples.Homeowner, General contractor3-4 weeks · Free
   2. 4.2Verify GC license, bond, insurance, and Seattle addition historyPull L&I status (active, bonded, insured), check recent Seattle addition permits, confirm RRP certification if your house is pre-1978, and walk one finished project. About 30 minutes plus a site visit.Homeowner1-2 days · Free
   3. 4.3Negotiate and sign the GC contractFixed-price is what most owners want. Cost-plus only works with a guaranteed maximum price (GMP) cap and weekly itemized invoices. On addition contracts (almost always over $300K), an attorney review pays for itself.Homeowner, General contractor, Attorney1-2 weeks · $1,000-$4,000 if attorney-reviewed
   4. 4.4Bind builder's risk + line up where the family livesGet the builder's risk policy in place before the GC mobilizes, and decide whether you're sheltering in place or moving out for 6-12 months. For most second-story additions, the answer is moving out.Insurance, Lender, Homeowner2-4 weeks · $800-$2,500 builder's risk + $20K-$60K temporary housing
6. Phase 5

   Build

   Mobilization to substantial completion. The longest phase by wall clock. Abatement first, then foundation work, then demo, then framing, MEP, finishes, inspections. Six months is fast; nine to twelve is realistic.

   6-12 months·Included in GC bid, plus $5K-$30K abatement·6 steps
   1. 5.1Lead and asbestos abatementIf the Phase 0 screen flagged either, a licensed abatement contractor removes the affected materials before the GC starts demo. Self-contained operation that runs for a few days to a couple of weeks, ahead of the rest of the build.General contractor3 days to 2 weeks · $5,000-$30,000
   2. 5.2Foundation retrofit, or lift + new foundationWhichever path Phase 2 picked: the structural retrofit happens now, before any framing on the second story can start. Retrofit is 2-4 weeks; a full lift + new foundation is 6-10 weeks.General contractor, Structural eng.2-10 weeks depending on path · $15K-$60K retrofit; $40K-$150K+ lift + new foundation
   3. 5.3Demolition + framing of the new second storyThe GC removes the existing roof, frames the new second-story walls, installs new floor joists (the old ceiling), reframes the new roof, and gets the building dry-in. The single most visually dramatic step of the whole project.General contractor6-10 weeks · Included in GC bid
   4. 5.4MEP rough-in + knob-and-tube remediationElectrician, plumber, and HVAC sub install rough wiring, pipes, and ducts in the new walls and (almost always) replace knob-and-tube wiring throughout the existing house. The house may need a service upgrade too.Electrician, Plumber, HVAC contractor4-6 weeks · $20K-$45K electrical (with rewire), $15K-$30K plumbing, $9K-$22K HVAC
   5. 5.5Insulation, drywall, finishesInsulation, drywall, cabinets, flooring, paint, fixtures, and appliances. The longest hands-on stretch — and the place where late finish decisions translate straight into budget creep.General contractor2-4 months · Included in GC bid; finish creep is common
   6. 5.6Required tests + inspections at each stageBlower-door test on the combined new + existing building, duct-leakage test, and SDCI inspections at foundation, framing, MEP rough, insulation, and final. The checkpoints between phases.Energy consultant, SDCI, General contractorOngoing across the build · $550-$1,050 for blower-door + duct tests
7. Phase 6

   Final inspection, move back in, and home record

   Substantial completion to legal occupancy. SDCI signs off the final inspection, the CofO issues, the family moves back in, and the lien-waiver file gets closed out. Then the project becomes part of the home record.

   3-6 weeks·Included in permit fee + moving cost·3 steps
   1. 6.1Final SDCI inspection + Certificate of OccupancyGC requests the final inspection; SDCI walks the building, signs off or issues a punch list, and on clearance issues the Certificate of Occupancy that makes the new space legally habitable.SDCI, General contractor1-3 weeks · Included in permit fee
   2. 6.2Move back in + walk the punch list with the GCFamily moves back into the finished house, and you walk the punch list with the GC over the next 30 days. Most punch items are minor; a few will surface only after you live in the space.Homeowner, General contractor2-4 weeks · Moving costs
   3. 6.3Update the home recordFile the permit close-out documents, the as-built drawings, the warranty paperwork, and the equipment manuals into the home record. This is the file your future buyer's title company will want to see.Homeowner1 week · Free