TownhomesModern Rowhomes
West Seattle
Attached ADU
ADU & Conversion
Permitting
Turn a basement, attic, or garage into a legal, code-compliant rental — and finally legalize work that was done without a permit.
An attached or interior ADU is often the lowest-cost way to add a unit, because the shell already exists. The catch is that converting non-habitable space into a legal dwelling triggers a specific stack of life-safety and energy requirements. We translate that stack into a clean submittal — and we handle the very common case where the space was already finished without permits.
What's included
- Conversion feasibility & code check
- Egress, energy, and fire-separation drawings
- Full SDCI permit package
- Unpermitted-work legalization strategy
- Trade-permit coordination
- Corrections handled to approval
01
Making a conversion legally habitable
A finished basement is not the same as a permitted dwelling. Egress, ceiling height, light and ventilation, fire separation, and a compliant separate entrance all have to be demonstrated on the drawings before SDCI will sign off.
- EERO emergency-escape egress windows for sleeping rooms
- Minimum ceiling-height verification
- Fire separation from the primary dwelling
- Separate entrance, light & ventilation
02
Energy code is where conversions stall
The Washington energy code applies to conditioned space you're now legalizing. Insulation, air-sealing, and mechanical documentation are the quiet reason conversion permits get kicked back. We document them up front.
03
Legalizing existing unpermitted work
If there's already a unit down there, you are not alone and you are not stuck. Legalizing as-built work before a sale or refinance is one of the most common calls we take. We document the existing conditions and bring them through SDCI with the least demolition and disruption the code allows.
- As-built documentation
- Targeted corrections, not a full teardown
- Clears title and refinance obstacles
Built & permitted
Attached ADUs we've
permitted & built.
Basement, garage, and addition conversions turned into legal, permitted units — our own builds. Open any project for the full photo set, then let's do the same with your lot.
Real projects
Permitted &
built in Seattle.
Every home here we designed, permitted, and built ourselves — our own developments across the Seattle area under Seattle Modern Buildings. All photos and details are genuinely ours, never stock. Drag or swipe to explore.
Townhomes
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New HomeCedar-Entry New Build
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New HomeRooftop Deck & Spa
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TownhomesInfill Townhomes
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DADUDetached Backyard Home
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ADURear Yard & Lower-Level Suite
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InteriorLight-Filled Open Kitchen
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TownhomesModern Rowhomes
West Seattle
New HomeSkyline Vantage
Seattle
New HomeCedar-Entry New Build
Seattle
New HomeRooftop Deck & Spa
Seattle
TownhomesInfill Townhomes
Seattle
DADUDetached Backyard Home
Seattle
ADURear Yard & Lower-Level Suite
Seattle
InteriorLight-Filled Open Kitchen
Seattle
ADU & Conversion Permitting — questions
What's the difference between an AADU and a DADU?
An AADU is attached to or inside your existing house (basement, attic, addition); a DADU is a separate detached structure. Current Seattle code lets most lots have one of each.
I already built a basement unit without a permit — now what?
We assess what exists, document the as-built conditions, and bring them through SDCI. In most cases we can legalize with targeted corrections rather than tearing finished work back out.
Ready to start your
ADU permit?
Tell us about your lot and project. We'll map the permit path and timeline before you spend on drawings.
Start Permit Review