Decks
What Is It?
A single-family deck is an outdoor platform built above the ground; it may or may not be attached to a house.
What Permits Do You Need?
You need a permit to build a deck if it is:
- More than 18 inches above the ground
- A roof deck (built on top of part of the building)
- In an environmentally critical area (ECA), for example for example landslide-prone or flood-prone areas.
Most decks require only a subject-to-field-inspection construction permit.
- Tip 312, Decks, Fences and Arbors for Single Family Homes in Seattle
- Tip 316, Subject-to-Field-Inspection Permits
You probably need an addition or alteration construction permit if your deck meets any of these criteria:
- It will be more than 8 feet above the ground
- It includes long beams
- It will be a roof deck
- It will be located in an environmentally critical area
Research the Code
Our Seattle Municipal Code (SMC) limits the size and placement of your deck.
If your deck is more than 36 inches above the ground: your deck counts toward the percentage of your property on which you can build (called lot coverage). That percentage varies by zone. For neighborhood residential zones (NR1, NR2, and NR3), the total coverage is limited to 35 percent of the lot (on lots 5,000 square feet or larger) or 1,000 square feet plus 15 percent of the lot area (on lots smaller than 5,000 square feet). For the residential small lot zone (RSL), the maximum lot coverage is 50 percent of the lot. We do not limit the size of decks that are less than 36 inches above the ground, unless you plan to build a deck in or near an ECA.
If your deck is more than 18 inches above the ground: you can’t build your deck within 20 feet of the front property line, or within 5 feet of either side property line in neighborhood residential zones (NR1, NR2, and NR3). You also cannot put the deck within 25 feet of the rear property line (or within the rear 20 percent of lot depth, whichever is less). In the residential small lot zone (RSL), you cannot put the deck within 10 feet of the front property line, with 5 feet of the side property lines or 10 feet within the rear property line (could be up to the property line abutting the alley). We do not limit the placement of decks less than 18 inches above the ground, unless you plan to build a deck in or near an ECA.
If your deck is in or near an ECA: you will need a pre-application site visit before applying for any construction permit (including subject-to-field inspection permits). We will determine what type of permit your project is eligible for based on the site visit. Read the Land Use Code and Environmentally Critical Areas Code for complete requirements, or contact the Applicant Services Center for land use, construction permit, or geotechnical coaching.
- Address Search for Property Information to find ECAs on your property
- SMC 23.44
Should You Hire a Professional?
Deck drawings rarely require a professional’s stamp indicating they were designed by an architect or engineer. Anyone with drafting skills may prepare the drawings, or you may hire a professional to help you.
If you plan to build a deck in or near an ECA, you need to follow specific rules for your project. You may want the help of a professional to prepare documents for your application and construction permit.