Seattle Deck Permit Guide for Homeowners (2026): When You Need a Permit

Decks are one of the most popular home improvements in Seattle — and one of the most common projects built without a required permit. Here is a clear guide to when you need a permit and what it involves.

When a Deck Requires a Permit in Seattle

A building permit is required for any deck that is:

• More than 30 inches above grade (measured from finished grade to the deck surface)
• Attached to the house (any height)
• Over 200 sq ft (detached, under 30 inches above grade)

In practice, most decks over 30″ above grade require a permit. Attached decks always require a permit because the attachment to the house ledger board requires structural review.

What the Permit Process Requires

• Site plan showing deck location relative to property lines
• Floor plan showing deck dimensions
• Structural drawings: footing design, beam and joist sizing, ledger connection detail
• Handrail and guardrail details (required for decks over 30″ above grade)

Structural Requirements

Seattle is in a high seismic and high-wind zone. Deck footings must be designed for frost depth (typically 18″ minimum) and lateral loads. Ledger connections to the house must be engineered to prevent separation — improperly attached ledgers are the most common cause of deck collapse.

Unpermitted Decks

Unpermitted decks create liability at sale (buyers’ inspectors flag them) and may require retroactive permitting or removal. The cost of permitting upfront is always less than the cost of dealing with unpermitted work at sale.

Cost of a Permitted Deck in Seattle (2026)

• Simple attached deck (200 sq ft): $25,000-$50,000
• Multi-level deck with roof: $60,000-$130,000
• Permit fees: $1,500-$4,000
• Architect/engineer fees: $4,000-$12,000

Piper Cole Architects designs and permits decks throughout the Seattle area. Free consultation — call 425-753-6452.