By Dawn Construction. Updated October 2026.
General information, not legal advice. Permit rules change. Confirm your project with the Seattle Department of Construction and Inspections (SDCI) before you build.
Do you need a permit to build a deck in Seattle?
Yes, if the deck is more than 18 inches above the ground, is a roof deck, or sits in an environmentally critical area such as a landslide-prone or flood-prone site. That is stricter than Renton and most Washington cities, which use 30 inches. Most Seattle decks need only a subject-to-field-inspection permit.
The 18-inch rule comes from SDCI's deck guidance and the Seattle Residential Code. Seattle also limits where a deck can go on your lot and how much of the lot it can cover, so a permit is only part of the plan.
Key facts: deck permits in Seattle
| Question | Short answer | Source |
|---|---|---|
| Height that triggers a permit | More than 18 inches above the ground | SDCI |
| Roof decks | Always need a permit | SDCI |
| Environmentally critical areas (ECAs) | Permit required, plus a pre-application site visit | SDCI |
| Usual permit type | Subject-to-field-inspection (STFI) construction permit | SDCI |
| Front setback (NR zones, deck over 18 in) | 20 feet from the front property line | SDCI |
| Lot coverage | Decks over 36 inches count toward lot coverage | SDCI |
| Guardrails | Required over 30 inches above adjacent surfaces | SDCI Tip 312 |
| Architect or engineer stamp | Rarely required | SDCI |
How is Seattle different from Renton and the rest of Washington?
Seattle's permit line is 12 inches lower than the common state threshold. A deck that would be exempt in Renton can need a permit in Seattle.
| City or rule | When a deck permit is required | Source |
|---|---|---|
| Seattle | More than 18 inches above the ground, any roof deck, or any deck in an ECA | SDCI |
| Renton | More than 30 inches above grade, measured within a 5-foot perimeter, or any work in a critical area | City of Renton |
| Common state exemption | Exempt only if 200 sq ft or less, 30 inches or less, freestanding, and not serving a required exit door | City of Federal Way |
Building in Renton instead? See our guide to deck permits in Renton, WA.
Which Seattle deck permit do you need?
Most decks need only a subject-to-field-inspection (STFI) construction permit. STFI is SDCI's simpler permit path for small projects, where an inspector checks the work in the field.
You probably need a full addition or alteration construction permit instead if the deck meets any of these conditions:
- It will be more than 8 feet above the ground.
- It includes long beams.
- It is a roof deck.
- It is in an environmentally critical area.
| Deck | Likely permit | Source |
|---|---|---|
| Platform 18 inches or lower, not in an ECA | No permit | SDCI |
| Typical backyard deck, 18 inches to 8 feet high | Subject-to-field-inspection permit | SDCI |
| Deck over 8 feet high or with long beams | Addition or alteration permit | SDCI |
| Roof deck | Addition or alteration permit | SDCI |
| Deck in or near an ECA | Site visit first, then the permit type SDCI decides | SDCI |
Where can you build a deck on a Seattle lot?
Once a deck is more than 18 inches above the ground, Seattle's zoning code controls where it can sit. Lower decks are not limited in placement unless they are in or near an ECA.
| Zone | Front | Sides | Rear |
|---|---|---|---|
| Neighborhood residential (NR1, NR2, NR3) | No closer than 20 feet | No closer than 5 feet | No closer than 25 feet, or the rear 20% of lot depth, whichever is less |
| Residential small lot (RSL) | No closer than 10 feet | No closer than 5 feet | No closer than 10 feet; may reach the lot line along an alley |
Source: SDCI deck guidance. These limits apply to decks more than 18 inches above the ground.
Does a deck count toward lot coverage in Seattle?
Only if it is more than 36 inches above the ground. Lot coverage is the share of your property that buildings and structures can cover, and it varies by zone.
- NR1, NR2, NR3, lots 5,000 sq ft or larger: total coverage limited to 35% of the lot.
- NR zones, lots under 5,000 sq ft: 1,000 sq ft plus 15% of the lot area.
- RSL zone: up to 50% of the lot.
If your house already uses most of the allowed coverage, a high deck may not fit. A deck at 36 inches or lower avoids the lot coverage count.
What if your lot is in an environmentally critical area?
Many Seattle lots sit on slopes or near water. If your deck is in or near an environmentally critical area, SDCI requires a pre-application site visit before you apply for any construction permit, including an STFI permit. SDCI decides the permit type after that visit.
Decks in or near an ECA have no exemption, even below 18 inches. SDCI suggests a professional may help prepare the application for these sites.
Do you need an architect or engineer for a Seattle deck?
Usually not. SDCI says deck drawings rarely need an architect's or engineer's stamp, and anyone with drafting skills may prepare them.
The drawings still need to be complete. SDCI's deck tip asks for items including a site plan and a scaled elevation drawing that shows the deck's height above the ground.
What safety rules apply to Seattle decks?
Seattle requires guardrails when a deck is more than 30 inches above adjacent surfaces, such as the ground. A permit-exempt deck still has to be built safely, so plan the height, stairs, and railings together.
For how decking materials hold up in our rain, see composite vs cedar vs pressure-treated decking.
Building a deck in Seattle: local details
- SDCI office: 700 5th Ave, Suite 2000, Seattle, WA 98104. Phone (206) 684-8600.
- Hillside lots: check for ECA mapping before you design; it adds a site visit to the timeline.
- Low decks near the street: decks 18 inches or lower are not limited in placement, unless they are in or near an ECA.
FAQ
How high can a deck be in Seattle without a permit?
Up to 18 inches above the ground, as long as it is not a roof deck and not in an environmentally critical area.
What is a subject-to-field-inspection permit?
It is SDCI's simpler construction permit for small projects. Most Seattle decks only need this type, with inspections done in the field.
How close to my property line can I build a deck in Seattle?
In NR zones, a deck over 18 inches high must stay 20 feet from the front, 5 feet from the sides, and 25 feet from the rear property line, or the rear 20% of lot depth if that is less.
Does my deck count toward lot coverage in Seattle?
Only if it is more than 36 inches above the ground.
Do I need a permit for a roof deck in Seattle?
Yes. Every roof deck needs a permit, and it usually needs an addition or alteration permit rather than the simpler STFI permit.
Do I need an engineer for my deck plans in Seattle?
Usually not. SDCI says deck drawings rarely need a professional's stamp.
Is the Seattle rule the same as in Renton?
No. Seattle requires a permit above 18 inches, while Renton uses 30 inches above grade.
Planning a deck in Seattle?
Dawn Construction builds composite, cedar, and pressure-treated decks for Seattle homeowners. Book a free estimate and we will check your height, setbacks, and permit type before you build.
Sources
- Seattle Department of Construction and Inspections, Decks: https://seattle.gov/sdci/permits/common-projects/decks
- SDCI Tip 312, Decks, Fences, and Arbors for Single-Family Homes in Seattle (updated August 14, 2024): https://www.seattle.gov/DPD/Publications/CAM/cam312.pdf
- SDCI, Do You Need a Permit?: https://www.seattle.gov/construction-and-inspections/permits/do-you-need-a-permit