We finish and convert a basement or daylight basement into a code-legal apartment, with egress windows, ceiling height fixes, moisture control, and a full kitchen and bath.
A basement conversion turns the space under your house into a legal apartment with its own kitchen, bath, and entrance. It is a great fit for the hillside homes around Bellingham with daylight basements, where a walk-out suite makes sense on a sloped lot. The work is more than drywall and trim, though. A legal basement unit needs proper egress windows for safety, enough ceiling height to meet code, and serious moisture control so it stays dry.
Our wet climate is the whole challenge here. A below-grade unit that is not sealed and ventilated right will grow mold and feel damp by the second winter. We handle the egress window wells, fix ceiling height where we can, manage the moisture with proper sealing and ventilation, and build a full kitchen and bath. We pull the permit with the City of Bellingham or Whatcom County and bring the unit up to current energy code so it lives like a real apartment, not a finished basement.
What it actually costs.
Basement conversion $90,000 to $180,000
Egress windowsCutting and waterproofing window wells in the foundation
Ceiling heightWhether the existing height meets code or needs work
Moisture controlSealing, drainage, and ventilation for our wet climate
Kitchen and bathAdding plumbing below grade and tying into the main lines
Our four-step process.
Free feasibility check
We check ceiling height, the foundation, and moisture conditions, and tell you whether the basement can become a legal unit.
Design and permit
We plan the egress, the layout, and the moisture system, then pull the permit with the City or County.
Convert and build
We cut egress windows, seal and ventilate, frame, run plumbing and electrical, and set the kitchen and bath.
Final inspection and walkthrough
We pass final inspection, walk it with you, and close out the punch list.
Why hire a real crew for this.
Code egress windows cut and waterproofed for safety
Moisture control built for our wet PNW winters
Great fit for hillside daylight-basement homes
Full kitchen and bath with its own entrance
Permit and inspections handled by us
Frequently asked questions.
How much does a basement conversion cost in Bellingham?
A basement apartment conversion in Bellingham usually runs $90,000 to $180,000. The cost depends most on egress windows, whether the ceiling height already meets code, and how much moisture control the space needs. Cutting egress wells into a concrete foundation and waterproofing them is real work, and our wet climate means the moisture system is not optional. We give you a line-item number after a site visit.
Does a basement apartment need an egress window in Bellingham?
Yes. Any below-grade room used for sleeping in a legal unit needs an emergency egress window or door that meets code for size and opening, plus a window well if it is below grade. This is a safety requirement, not a nice-to-have, and it is one of the first things an inspector checks. We size, cut, and waterproof the egress as part of every basement conversion.
Can a daylight basement become an ADU in Bellingham?
A daylight basement is often the easiest basement to convert, because the walk-out side already gives you a real entrance and natural light. Bellingham has a lot of hillside lots where this works well. We still handle egress on any below-grade bedrooms, confirm ceiling height, and build the moisture and ventilation system so the unit stays dry. We confirm your lot allows it during the feasibility check.
Ready for a free basement conversion quote?
Tell us about your project and your lot. We'll reply within 15 minutes during business hours.