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June 1, 2026
How to Add a Bedroom to Your House in Seattle: Options, Permits, and Costs
Adding a bedroom is one of the most common reasons Seattle homeowners call an architect. There are several ways to do it, each with different costs and complexity. Here is a complete guide.
Option 1: Convert Existing Space
The most affordable path. Converting a den, bonus room, or large closet into a bedroom. To legally count as a bedroom, the room needs an egress window (5.7 sq ft opening), a closet, and minimum 70 sq ft floor area with 7 ft ceiling height.
Cost: $10,000 to $35,000 depending on whether egress work is needed.
Option 2: Finish a Basement or Attic
Converting unfinished basement or attic space adds a bedroom without expanding the footprint. Basement bedrooms require egress windows. Attic bedrooms require adequate headroom (7 ft over at least half the floor area).
Cost: $25,000 to $70,000.
Option 3: Build an Addition
A room addition adds a bedroom at grade or as part of a second story. This is the most expensive but adds the most value and flexibility.
Cost: $80,000 to $200,000 for a bedroom and bathroom suite.
Option 4: ADU for a Separate Bedroom Suite
If you need a private guest or in-law space, an ADU provides a full separate living unit. See our ADU design service.
Which Requires a Permit?
Any option involving structural changes, new egress windows, or new square footage requires a building permit. Simple conversions of already-conforming rooms may not.
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