Converting a garage is the most affordable way to add a legal living unit to a Bellingham property, which is exactly why it is one of the most common projects we do. In 2026, a garage conversion in Bellingham costs $80,000 to $150,000. The biggest swing in that range is whether the garage is attached to your house or detached in the backyard. This guide explains the difference, what a real conversion includes, and how to read a quote so you know you are comparing the same scope.
Attached vs. detached: the cost difference.
An attached garage shares a wall with your house, which means the water, sewer, and electrical are right there. A detached garage sits on its own in the backyard, so utilities have to be trenched and run out to it. That difference is the main reason a detached conversion costs more.
| Conversion type | 2026 Bellingham range | Why |
|---|---|---|
| Attached garage | $80,000 to $120,000 | Utilities are close to the house |
| Detached garage | $100,000 to $150,000 | Add 20% to 30% for utility runs |
So a detached garage typically runs 20% to 30% more than the same-size attached one, almost entirely because of the trenching and the new utility connections. The building work itself is similar.
What a real garage conversion includes.
A legal living unit is much more than drywall over the studs. Here is what is actually in a proper Bellingham garage conversion:
- Insulation and air sealing to current Washington energy code, because most garages were built with uninsulated walls.
- Slab and moisture work, since many garage slabs were poured with no vapor barrier and will grow mold without it.
- A kitchen and a bathroom, with the plumbing run to make them work.
- New windows and a real entry door in place of the old roll-up garage door, including the wall framing to fill it in.
- Electrical, often including a panel upgrade so the unit can run a kitchen and a heat pump without tripping.
- Egress, meaning a code-compliant window or door in any sleeping room.
- Heating and ventilation, usually a ductless heat pump, sized for the space.
The garage conversion service page covers the full process, and our guide to what you can build on your lot explains the 2026 rules that decide whether a detached garage can become a legal unit.
Why the cost per square foot is similar to new.
People expect a conversion to be dramatically cheaper per square foot than a new cottage. On total dollars it is, because a garage is smaller and the shell exists. But per square foot, the numbers get close once you add everything above. A kitchen, a bathroom, insulation, egress, and utilities cost roughly the same whether the unit is new or converted. The savings come from not building a foundation, walls, and a roof, not from the finishes. We give you both the conversion number and a comparable detached cottage number so you can decide.
The Bellingham climate factor.
Our wet winters make the moisture work non-negotiable on a garage conversion. A converted garage with an unsealed slab and poor ventilation will feel damp and can grow mold by the second winter. A proper conversion includes sealing the slab, insulating to code, and adding ventilation so the unit stays dry. Skipping this to save a few thousand dollars is the most expensive shortcut you can take, because it turns into a health and repair problem later.
How to read a quote.
When you compare garage conversion quotes in Bellingham, make sure each one spells out:
- Whether the price includes the utility runs (critical for a detached garage).
- The insulation and moisture scope, specifically.
- Whether an electrical panel upgrade is included or extra.
- The heating system and how it is sized.
- Permit and inspection fees, and who pulls the permit.
A one-line price is not a quote, it is a guess. A real quote tells you exactly what you are buying.
Frequently asked questions.
How much does it cost to convert a garage to an apartment in Bellingham?
A garage-to-apartment conversion in Bellingham costs $80,000 to $150,000 in 2026. An attached garage lands on the lower end because utilities are close, and a detached garage adds 20% to 30% for the water, sewer, and power runs. The price covers framing, insulation, a kitchen and bath, new windows, egress, and the electrical and plumbing to make it a legal unit.
Why does a detached garage conversion cost more?
Because the utilities are not right there. A detached garage needs water and sewer trenched out to it from your main lines and a power run from the panel, sometimes with a panel upgrade to carry the second unit. That extra trenching and connection work typically adds 20% to 30% over an attached conversion, where the utilities are already next to the house.
Can any garage be converted into a legal ADU in Bellingham?
Most can, but it depends on your lot. Under Bellingham's 2025 rules, most single-family lots can now have up to two ADUs, and a garage conversion counts as one. Setbacks, lot coverage, and ceiling height decide whether your specific garage qualifies, which is what our free feasibility check confirms before any design work.
Do I need a permit to convert my garage in Bellingham?
Yes. Converting a garage into a living unit changes its use and requires a permit through the City of Bellingham or Whatcom County, plus inspections during construction. We handle the full permit package and the inspections as part of the project, so you do not have to navigate the counter yourself.
For a free feasibility check and a written, line-item quote, Bellingham ADU Co. handles garage conversions across Bellingham and Whatcom County.