Could You Build an ADU? What Portland & Vancouver Homeowners Should Know
Sep 8
4 min read
A big backyard used to mostly mean more grass to mow.
Today, I look at it differently.
When I'm walking a property in Portland or Vancouver and see a large yard, oversized garage, basement, or unused side yard, one of the questions that comes to mind is:
Could another dwelling work here?
The answer is increasingly maybe.
ADU Rules Have Changed
Portland's residential zoning has become considerably more flexible.
A house can generally have one ADU, and qualifying properties can accommodate two ADUs. Portland also allows duplexes, triplexes, fourplexes and cottage clusters in many residential zones.
Across the river, Vancouver currently allows up to two ADUs on a lot, subject to its zoning and development requirements.
That's a pretty significant change in what an ordinary residential property can potentially do.
What Exactly Is an ADU?
Think of an ADU as a smaller independent home associated with another residetial property.
It needs its own living facilities—including space for cooking, sleeping and a bathroom.
Depending on the property, it might be:
A detached backyard cottage
A converted garage
Part of the existing house
A basement conversion
An addition to the house
Portland specifically recognizes conversions of parts of a home, garages/accessory structures, additions and newly constructed detached ADUs.
Why Would Someone Want One?
Rental income is the obvious answer.
But I actually think flexibility is the more interesting part.
An ADU could potentially provide:
Long-term rental housing
A home for an aging parent
Independent space for an adult child
Guest quarters
A private home office
Future downsizing options
Someone could even live in the smaller unit and rent the larger house someday.
That's a lot of flexibility from one property.
Portland Allows More Than Many Owners Realize
Portland's current residential infill rules go considerably beyond simply allowing a backyard cottage.
Depending on zoning, lot size and other property characteristics, residential development can include ADUs, duplexes, triplexes, fourplexes and cottage clusters.
There is even a Middle Housing Land Division process that can allow qualfying duplex, triplex, fourplex or cottage-cluster units to sit on separate lots and therefore be sold individually. It does not apply to a house-plus-ADU configuration.
That's why I don't automatically look at every Portland lot as simply “one house.”
Vancouver Has Become More Flexible Too
Vancouver allows ADUs in Low-Scale and Medium-Scale Neighborhood zoning districts, with possibilities in some other districts as well.
Current city guidance says:
Up to two ADUs can be built on a lot.
They may be attached, detached or conversions.
Owner occupancy isn't required.
There is no minimum vehicle-parking requirement specifically for an ADU.
A unit must be 1,000 square feet or less to be considered an ADU and receive reduced impact fees.
That creates some interesting opportunities for SW Washington homeowners and investors.
But Don't Assume You Can Build One
This is the important part.
Seeing a large backyard doesn't mean I would advertise a property as “ADU ready.”
Before spending money—or marketing development potential—you need to investigate things like:
Zoning
Lot dimensions
Setbacks
Existing structures
Sewer or septic capacity
Water service
Stormwater requirements
Utility locations
Building-code requirements
Access
Construction cost
Portland specifically warns that adding dwelling units can trigger infrastructure upgrades involving water, sewer, stormwater, streets or street trees.
Vancouver similarly requires a utility-services review before a residential building application for new housing such as an ADU.
Sellers: Don't Ignore Development Potential
This is where it becomes especially relevant to real estate.
Imagine two otherwise similar homes.
One has a normal backyard.
The other has zoning, lot configuration and utilities that may allow another dwelling.
Those aren't necessarily identical properties from a buyers perspective.
That doesn't mean I'd arbitrarily add $10,000 to the asking price because an ADU might be possible.
But I absolutely want to understand that potential before we market the property.
Sometimes the buyer who sees the most value in a property isn't looking for the prettiest backyard.
They're looking at what they might be able to do with it.
Buyers Should Think About This Too
If you're shopping for a home and think an ADU might be part of your future, tell your agent before you start looking.
We can pay more attention to:
Lot configuration
Garage placement
Basement layouts
Side-yard access
Zoning
Utility considerations
You may not build anything for five years.
But buying a property that gives you that option can be very different from discovering five years later that your lot won't accommodate what you had in mind.
Bottom Line
I think one of the most interesting changes happening in Portland and SW Washington real estate is that we're slowly moving away from the idea that every residential lot has one—and only one—possible use.
Some properties have considerably more flexibility.
The key is figuring that out before you buy, sell, or spend money designing something.
If you're considering selling a Portland or SW Washington property with a large lot, basement, detached garage, or possible development potential, I can help you identify the questions we should answer before putting it on the market.
My full-service listing representation is 1.25%, including professional marketing, pricing strategy, negotiation, and transaction management.
For homeowners who want to investigate the rules themselves, the City of Portland Residential Infill guide and City of Vancouver ADU guide are good starting points.
