Are MDUs coming to Bellingham?

Jace Cotton is excited about tiny homes. That’s notable, given that Jace is a Bellingham City Council member At-Large and excitement about tiny homes at that level of local government has, historically, been in short supply. Cotton has drafted a memorandum to the full city council proposing that Bellingham legalize what the memo calls “movable dwelling units” (also referred to as MDUs)— tiny homes on wheels and RVs — as backyard housing. For anyone who builds tiny homes in this town, or who wants to live in one, this is worth paying attention to.

Why Now

The housing numbers in Bellingham are grim. As measured by median home price to average area income, Bellingham is currently the fourth most unaffordable city in the country. Almost a quarter of homeowners and more than half of renters here are housing cost burdened. The December 2025 Housing Pool Report counted 315 unhoused households in Whatcom County, and the waitlist for North Haven, the local low income tiny home community, has over 2,100 people on it.

Against that backdrop, the existing city code, which prohibits tiny homes and RVs as permanent residences outside of manufactured home communities, looks increasingly difficult to justify. Cotton’s memo makes the case that legalizing backyard MDUs is one of the few housing strategies that doesn’t require subsidies, doesn’t require developers, and can happen fast.

This Is Already Working in Portland

You might think, “Wait a minute. This is crazy. Could it really work?”

Portland legalized occupied residential vehicles — THOWs and RVs — in all residential zones in 2021. The results have been watched closely by housing advocates and city planners around the region, and the numbers are encouraging. A survey of one Portland neighborhood of about 4,500 households found 65 backyard MDUs in 2020, before legalization. By 2024 that number had grown to 94. Extrapolating that density across the city suggests well over 3,000 units currently in use.

One Portland homeowner was able to move her mother-in-law into her backyard. An MDU, she said, “ended up being realistically our only option — other than her being homeless, really.” Kol Peterson, a tiny house advocate who has studied Portland’s approach closely, noted his own surprise at how well it worked, describing a lesson for other cities that “not only could a significantly liberalized approach toward the habitation of THOWs and RVs on residential properties incrementally help solve the affordable housing crisis, but perhaps they can do so with fairly broad public support. And quickly.”

Port Townsend took a more restrictive approach in 2023, limiting allowable units to more expensive factory-certified models with additional requirements layered on. The result: a single permitted THOW. The lesson is not complicated. When you make the rules accessible, people use them. When you don’t, they don’t.

Let’s Address the Understandable Fear

Anyone who drives along the industrial area of Cornwall Avenue has seen the other version of this story: aging RVs parked wherever enforcement is thin, in varying states of disrepair, with no utilities, no sanitation plan, and no real relationship to the surrounding neighborhood. That image is going to be in many people’s minds when the city council considers this proposal, and it’s a fair thing to raise. The question worth asking, though, is whether the answer to that situation is to keep the current prohibition — which hasn’t made those RVs go away — or to create a legal framework that sets standards, and brings the whole arrangement into the open. Cotton’s proposal is aimed squarely at the latter. A backyard MDU operating under a permit, connected to sewer and water, with a written tenancy agreement, is not the same thing as an an illegally parked RV surrounded by old bikes and dilapidated barbecues.

The Important Questions

Where could you actually put and MDU? Under Cotton’s proposal, any residential lot with a primary dwelling could host one MDU. Lots larger than 10,000 square feet could host two. The MDU goes in the backyard — or wherever it fits on the property — and connects to the utilities already serving the main house.

How complicated are those utility connections?  Water comes from a potable-rated hose bib on the exterior of the primary dwelling — essentially the same connection as a garden hose, but rated for drinking water. Electrical is a 50-amp shore power connection, the same standard used at RV parks across North America. Sewer connects to the existing lateral line. The total estimated cost for all three connections is under $15,000 — a fraction of the $250,000 to $450,000 it currently costs to build a traditional detached accessory dwelling unit in Bellingham.

Is this going to turn into a front-lawn Airbnb situation? The proposal explicitly prohibits short-term rentals. An MDU on a residential lot would have to be someone’s actual home. This is both a practical and a political choice — it keeps the focus on housing rather than hospitality, and it preempts the most obvious neighborhood objection.

What does the permitting look like? Cotton’s proposal requires a permit for placement and a written lease agreement between the property owner and the MDU resident. The permit creates a paper trail, which is useful for the city to track what’s actually happening. Beyond that, the regulatory footprint is intentionally light.

What It Means Here

Right now, Bellingham Municipal Code Section 20.10.030 flatly prohibits this. Whatever your situation — a homeowner who wants to house a family member, an adult child who wants to park a tiny home in a parent’s backyard, someone who owns a THOW and is looking for a legal place to put it — the current code offers no path.

Cotton’s proposal doesn’t guarantee anything yet. It’s the beginning of a conversation. But for tiny home builders and enthusiasts, it is an exciting development.

Mount Baker Tiny Homes builds custom tiny homes on wheels and van conversions in Bellingham, Washington. Get in touch if you want to talk through a build.