A single-family deck is an outdoor platform built above the ground; it may or may not be attached to a house.
You need a construction permit to build a deck that is more than 18 inches above the ground or that is a roof deck (built on top of part of the building). You need a construction permit to build a deck of any height in an environmentally critical area (ECA), for example landslide-prone areas.
Most decks require only a subject-to-field-inspection construction permit. Subject-to-field-inspection permits are issued over the counter, typically on the day you apply.
Our Seattle Municipal Code (SMC) and Seattle Residential Code (SRC) limit 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 single-family zones, 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). 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 single-family zones. 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). 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 visit the Applicant Services Center for land use, construction permit, or geotechnical coaching.
Deck drawings rarely require a professional’s stamp indicating they were designed by an architect or engineer. You may prepare the drawings yourself or 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.