Washington’s ADU Surge Leads the Nation [6/18/26]
June 18, 2026
Michael Pierce

Washington’s ADU Surge Leads the Nation [6/18/26]

Today we’re talking about ADUs — accessory dwelling units.

Backyard cottages.
Garage apartments.
Basement conversions.
Tiny detached homes quietly appearing behind single-family houses while neighbors pretend not to notice during HOA meetings.

And suddenly ADUs are becoming one of the biggest housing policy stories in the country.

A new report says the national ADU housing market has now reached more than $21 billion.

And Washington State has emerged as one of the country’s most aggressive pro-ADU jurisdictions.

The big catalyst is HB 1337, which took effect in 2025.

The law requires cities and counties to allow at least two ADUs per residential lot and removes many traditional barriers like owner-occupancy requirements.

That is a major philosophical shift in housing policy.

Historically, many local governments made ADUs technically legal but practically difficult.

Height limits.
Parking mandates.
Setback requirements.
Utility fees.
Street improvement demands.
Lengthy review processes.

In some places, it almost felt like cities were saying:
“Yes, you may absolutely build housing… as long as you survive twelve side quests and a blood oath first.”

Washington’s new framework changes much of that.

The state is increasingly using preemption — meaning statewide rules overriding local restrictions — to encourage more housing flexibility.

And this matters far beyond backyard cottages.

Because ADUs reflect a broader policy direction:
more density,
more infill,
more flexibility,
and fewer local veto points.

That trend could eventually influence broader multifamily zoning and development policy too.

Now ADUs are not traditional multifamily housing.

A backyard cottage in Tacoma is not replacing a 250-unit apartment tower in Bellevue.

But collectively, ADUs create what economists sometimes call shadow supply.

Small incremental housing additions scattered throughout neighborhoods.

One extra unit here.
Two extra units there.

Individually small.
Collectively meaningful.

This is especially true in expensive West Coast cities, where every additional housing unit matters.

The report notes that detached ADUs in the Seattle region can still cost hundreds of thousands of dollars to build.

This is not exactly cheap housing.

Construction costs remain high.
Financing can be difficult.
Permitting still takes time.

Because even when housing policy improves, physics and labor invoices continue existing stubbornly.

But compared to buying a full single-family home in Seattle, ADUs can still create relatively attainable housing options.

For apartment owners, ADUs probably do not represent a massive direct competitive threat.

The scale simply is not large enough.

But they do matter symbolically.

They reveal where housing policy is heading.

Washington increasingly favors density, infill development, and state-level intervention to override restrictive local zoning systems.

That policy framework could eventually create broader multifamily opportunities as well.

At the same time, Washington’s economy remains steadier than Oregon’s in many investor discussions, though the state is hardly immune from slower hiring or affordability pressures.

Job growth has moderated.
Unemployment remains elevated compared to the ultra-tight labor markets of earlier years.
And renters continue facing significant affordability challenges.

So this is not some euphoric boom environment.

But Washington still maintains a stronger long-term growth narrative than many West Coast markets.

And housing flexibility remains central to that story.

The future housing market may not arrive entirely through giant downtown towers.

Some of it may arrive quietly… one backyard cottage at a time.

HFO Investment Real Estate is Oregon’s and SW Washington’s leading multifamily brokerage by transaction volume.

 

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