by Michael Andersen — images by Courtney Ferris

Yesterday, in a post that visualized the spread of startlingly expensive housing across Portland, we shared some images of the sort of buildings that Portland is considering re-legalizing in many of its residential areas.

Buildings like this triplex:

A 2,500-square-foot triplex, the maximum size allowed under the city’s latest proposal.

Some Portlanders are very, very upset about this idea. In August, one group marched through Southwest Portland with preprinted signs saying “Don’t Rezone Us.” In a blog post yesterday, Margaret Davis of United Neighborhoods for Reform described the concept as “rezoning huge swathes of the city.”

The building on the above right is what they’re talking about.

There are lots of buildings like it scattered through Portland’s neighborhoods already. But almost none of them are new, because in 1959 the city made it illegal to build any more triplexes in most Portland residential areas.

This is what’s currently legal to build instead of triplexes:

The maximum single family home size allowed under current law. The city’s proposal is to change this.

To be fair, the 6,000 square foot McPalace on the right is the largest that could possibly be built, not what is currently being built. Last time the city checked (in 2013) most new homes on standard residential lots were between 2,500 and 4,000 square feet, and it’s unlikely that they’ve shrunk since.

By comparison, the “typical Portland home” pictured on the left, hypothetically built in 1920, is 1,700 square feet. (Not counting that cool porch.)

The city’s most recent proposal is to cap all new buildings on standard lots at 2,500 square feet total. This would prevent the largest 60 percent of new single-family homes — the McMansions, in other words — from ever being built.

Houses up to 2,500 square feet would still be allowed. Here’s what the proposed new maximum would look like:

A recent economic study concluded that this new maximum on the size of homes would reduce the number of demolitions in the city over the next 20 years. That’s because with smaller maximum home sizes, demolitions would become less profitable.

Mostly, this would happen by reducing the number of 1:1 demolitions (McMansions) and 1:2 demolitions (“skinny houses”).

Legalizing triplexes would not mean most houses would suddenly be knocked down to build a triplex

This seems to be the fear expressed by people like Davis or Midge Pierce of the Southeast Examiner (another vocal critic) and it’s understandable. But the key reason why this wouldn’t happen, according to the economic study, is the new cap on building size.

For a demolition to occur, one simple thing needs to be true: a building needs to be more valuable as vacant land than it is as a building. Here’s the algebra of demolition:

purchase price of old building + construction cost of new building < sale price of new building

If that formula isn’t true, then demolition won’t happen.

By shrinking the size of new buildings, we as a city would greatly reduce their potential sale price, and therefore the number of demolitions that are viable.

Here is a map of where demolitions would be viable over the next 20 years (in red) without the residential infill project. Much of Cully, St. Johns and southwest Portland would gradually be replaced by McMansions.

And here’s where it would be likely with the residential infill project. Cully, St. Johns and southwest Portland would still see most of the change, but they’d see notably less.

The other difference is that when demolitions do occur, the city’s proposal would ensure that instead of replacing one small home with one huge home, they’d replace one small with two or three small homes — reducing displacement instead of enabling it.

To actually reduce home prices, we need to legalize small homes as well as blocking big ones

Unfortunately, simply reducing demolition wouldn’t do anything to help Portland’s affordability problem, which is one of the goals of the residential infill project. If all building in the city stopped tomorrow, it’d only accelerate the process by which tens of thousands of little old bungalows are gradually becoming as expensive as McMansions.

That’s why the city is also considering re-legalizing duplexes in residential zones, up to exactly the same size as new single-family homes:

A 2,500 square foot duplex (two adjoined 1,250 square foot homes), the maximum size proposed for a standard lot.

The city might also legalize backyard cottages on the same lot as a duplex, as long as their combined square footage is 2,500 square feet:

A 700-square-foot accessory unit on the same lot as an 1,800-square-foot duplex.

Another idea that isn’t in the city’s latest proposal, but which could be, would be to make it legal to put a fourth unit on a lot … as long as at least one of the four is both affordable to lower-income households and accessible to people with disabilities.

Or (stand by for an animated GIF) the city could take a further step toward preventing demolition by making it legal to internally divide an old building into multiple homes. There could be lots of options for this, as long as the structure and any on-site trees are preserved:

Of these options, only the last one — the four-plex with a cost-control requirement — would directly create a new home that’s affordable to lower-income Portlanders. Again, this isn’t part of the city’s latest proposal.

The other ideas above do advance affordability, though:

They’d slow price increases citywide by creating additional homes that give middle-class people somewhere to move that doesn’t displace a poor person. They’d make it possible for more homes in Portland’s residential zones to be within reach of the city’s middle class.

Most Portlanders would probably agree that both of these goals are good. But most Portlanders probably want lower-income people to benefit from housing policy changes, too. In my next post, I’ll look at the residential infill project from the perspective of lower-income Portlanders.

Portland for Everyone supports abundant, diverse, affordable housing. This blog is a reported effort to explore the ways to achieve those goals. You can get involved in Portland for Everyone’s organizing work here.