What Are The New ADU Laws for Bellingham and Whatcom County 2025

Let’s face it: housing in Whatcom County is tighter than your neighbor’s jeans after Thanksgiving. But good news—2025 just kicked the door wide open for homeowners who’ve been thinking about building an ADU (Accessory Dwelling Unit) but never pulled the trigger because... bureaucracy.

That changes now.

Washington State has decided that red tape is out, and backyard cottages are in. So, whether you're looking to add a little rental income, stash your in-laws somewhere other than your guest room, or finally build that detached studio you keep telling your friends is “in progress,” this is your year.

Welcome to your no-BS, guide to building, permitting, and profiting from an ADU in Whatcom County—minus the municipal migraine.

The ADU Revolution: Why 2025 Is the Year to Actually Do the Thing

First off, here’s why you should care:

• You can now legally rent out both your house and your ADU without pretending to live in either.

• You don’t need to pave a parking lot just to build a 600 sq ft studio.

• Your city can’t tell you your ADU is “too big” if it’s under 1,000 sq ft.

• Permits are (theoretically) going to be faster and less annoying.

• And yes, your property value might go up, like, significantly.

All thanks to House Bill 1337 and the 2025 Comprehensive Plan Update—two wildly boring government documents that, for once, actually do something useful.

The Five Big Changes (a.k.a. Why You Can Finally Build That Backyard Bungalow)

1. Live Where You Want, Rent What You Want

Old Rule: You had to live on the property to have an ADU.
2025 Rule: You don’t. At all.

That means:

• You can rent out both the main house and the ADU.

• You can move to Portugal and still collect rent.

• You can stop submitting weird affidavits to Bellingham once a year.

Just don’t try this in the Lake Whatcom Watershed unless you enjoy rejection.

2. Bigger is Better—And Now It’s Legal

Old Rule: Size limits were weird and inconsistent.
2025 Rule: All cities must allow at least 1,000 sq ft.

In Bellingham, if you match your ADU’s roof pitch and siding to your main house, the city might just give you extra square footage as a reward for being a good design citizen.

3. The Parking Spot That No Longer Needs to Exist

Old Rule: One parking space per ADU bedroom.
2025 Rule: LOL, nope.

If you’re near a WTA bus stop or have street parking, you’re good. That means no digging up your yard to create a parking spot for your tenant’s Subaru. Saves you $5,000–$15,000 and one less existential crisis.

4. Permits: Slightly Less Soul-Crushing Now

Cities are getting their act together (finally):

• Bellingham: Projects under 1,000 sq ft now get streamlined approvals with zero neighbor tattletales.

• Ferndale/Blaine: Pre-approved plans to skip the permit purgatory.

• Rural Whatcom: If you’ve got 4.5+ acres, your life just got easier.

Hot tip: Submit your permit before June 2025 to lock in current fees—because they’re likely going up.

5. City-Specific Shenanigans You Should Know About

Bellingham:

• Two ADUs per lot allowed (1 attached, 1 detached).

• Lake Whatcom = zero fun, highly regulated.

Ferndale:

• No more Conditional Use Permits for under 1,000 sq ft.

• You don’t need your ADU to look like a mini-me of your main house anymore.

Lynden:

• You can now build two-bedroom ADUs!

• But detached units still need serious land (4.5+ acres).

Blaine:

• Pre-approved plans = faster builds.

• Short-term rentals like Airbnb? Not in residential zones, buddy.

So… Should You Build an ADU?

Only if you like:
✅ More income
✅ Higher property value
✅ Housing options for your parents/kids/friends/tenants
✅ Feeling smug at parties because you actually used your backyard

Don’t Screw It Up: Mistakes to Avoid

• Lake Whatcom rules still apply. You can’t just drop a tiny home and call it good.

• HOAs can still crush your dreams. Sudden Valley, we’re looking at you.

• Your 1926 sewer line might cost you $20K. Plan for utility upgrades.

Final Checklist (Because Yes, You’re an Adult and This is Real Now)

✅ Know Your Zoning: Use Whatcom County’s parcel viewer—don’t wing it.
✅ Get Pre-Approved: WECU and Peoples Bank have ADU-specific loans.
✅ Design Smart: Transit proximity = no parking requirement = cheaper build.
✅ Act Fast: Permits submitted before June 2025 may qualify for fee breaks.
✅ Book a Pro: Get a site analysis done before you start dreaming too hard.

Want to see a cool company that is building modular ADUS for a very reasonable price, check out MOMO HOMES