Most Portlanders probably know of at least one or two old houses that have been knocked down to build big new ones. Many people don’t like it when that happens.

Portland’s residential infill proposal takes a creative approach to making this happen less. If a developer isn’t allowed to build a house that’s big enough to sell for $800,000, they won’t be able to afford to pay $300,000 for the old house.

In that situation, the old house would remain — because the person who wants to buy and live in the old house for $300,000 won’t have to compete against a developer.

In Portland’s most common zone, R5, the city proposes to cap the size of a new building at 1/2 the square footage of the lot underneath: 2,500 for a standard 5,000-square-foot lot.

In 2015, 76 percent of the 275 new homes built in Portland’s most common zone, R5, were bigger than that ratio. If the new proposed rules had been in effect, those new McMansions would have been illegal.

But today, those McMansions affordable primarily to millionaires are exactly what current city code encourages.

Here’s a photo montage that shows the difference between the sort of homes allowed today in most of Portland and the sort of homes that are forbidden:

Here are the main details that have changed since last fall

My colleague Madeline Kovacs and I have spent the last week poring over what’s new in last week’s draft. Here’s a quick summary — we’ll be digging further into each of these and more in the next few weeks, and I’ll be sharing more here on the blog.

1. The area where “missing middle” housing would be re-legalized got a bit smaller.

Duplexes, corner triplexes and second ADUs would be allowed in the yellow area, but only subject to the new citywide size limits. (Because the proposal doesn’t affect areas that already allow full-size attached homes, those denser areas are in white on this map.)

Last year, the city floated an initial map of the area where certain “missing middle” duplexes, corner triplexes and second granny flats would be allowed. (In the case of the second accessory dwelling unit, the city would allow one attached ADU and one detached ADU per lot: one converted basement and one converted garage, for example.)

This year’s map has changed a bit to prioritize proximity to amenities such as community centers, parks, schools and transit lines. The idea is that the public can get more out of its amenities — and help more people get to them without cars — if more of the public are allowed to live near them.

Meanwhile, in an effort to minimize site-specific displacement, the city removed areas with more people at risk of immediate displacement. (We’ll explore this idea more closely in a future post.)

The final result: parts of East Portland, northeast Cully, the northern St. Johns Peninsula and far Southwest Portland have been removed, while some mostly closer-in areas have been added.

2. If you’re building “missing middle” homes on a lot, at least one of the homes would need to be universally “visitable.”

To be “visitable” by people with mobility issues — a group expected to grow rapidly as Boomers age — a home must have “a low- or no-step entry, wider halls and doors, and living space and bathroom on the ground floor.” This standard would apply to any lots getting new duplexes, triplexes or second ADUs.

3. One “bonus unit” would be allowed if every home on the lot would be affordable to lower-middle-income households.

This could allow midblock triplexes and corner four-plexes, but because of the price limitation it would probably be fairly rare. Nonprofits such as Habitat for Humanity, whose work is to lower homeownership barriers by combining multiple subsidy programs from various governments, might or might not be able to make this work. We’ll be talking to some experts in the coming weeks in an effort to find out.

4. A bunch of rules for skinny houses have changed.

Many skinny houses would be essentially capped at two stories, with fewer front-facing garages, under the proposed rules.

The council resolution last fall called for various new restrictions on building skinny houses on narrow lots. That’s reflected in the new code, which would put a new cap on the height of detached homes on lots that are less than 36 feet wide. (A standard Portland residential lot is 50 feet wide.)

Under the new rules, a detached house on one of these lots can be only 1.5 times as tall as it is wide. So a 16-foot wide detached house on a 26-foot-wide lot could only be 24 feet high — two stories plus an attic, in other words.

New homes on adjoining lots of 25 feet or less, meanwhile, would have to be attached to another house, sharing walls along their lot lines (and therefore having a bigger side or back yard instead of uselessly small ones on each side).

There are various other tweaks, including a change to parking rules. Because driveways eliminate curbside parking spaces, they’re particularly counterproductive on narrow lots, and would no longer be required.

5. Buildings designated as historic would get extra demolition protection.

Sometimes, the best way to keep an old house standing is to internally divide it into two or three smaller homes. After that, it’d become significantly less profitable for someone to tear the whole thing down.

That’s the new historic preservation angle in the city’s proposal, which would allow new duplexes, triplexes and second ADUs on lots with historic buildings (including buildings officially marked as “contributing” to a historic district such as Irvington) only in one situation: if the old structure remains standing.

If a landowner does that — either by internally dividing the old structure to create multiple homes inside, or by adding more small homes to the lot — they get slightly more flexibility, such as two detached ADUs per lot, the option for a mid-block triplex and (to encourage garage conversions) no on-site parking minimum.

Conclusion: Portland’s main housing problem is that even its cheap homes are no longer cheap

1603 SE Salmon Street, built in 1890.

As the map near the top of this post showed, Portland’s status quo is malfunctioning. Even little old homes that are sort of falling apart are ridiculously expensive now.

This is because the land beneath Portland’s buildings, old and new, has gotten more desirable.

Portland has spent a lot of energy debating various short-term responses to the resulting housing crisis, and those are essential too. But there are also a couple ways Portland could address this fundamental problem over the long term.

One response would be to make Portland a less desirable place to live: fewer jobs, slower public transit, uglier parks, worse restaurants.

But there’s also a second solution to the problem of increasingly valuable land: Share the land.

For centuries, this has has been the usual way cities have dealt with the process of becoming more popular.

Instead of requiring everyone who wants to live in a residential neighborhood to rent or own a certain minimum amount of increasingly expensive dirt, we could make it legal for multiple households to split the cost.

A 2,500-square-foot triplex.

We would do this by making it legal to put homes next to each other, or on top of one another.

It’s no great mystery how to do this — Portlanders were doing it for decades before 1959, when the city council voted to ban small multi-home buildings from most of the city.

A duplex off Northwest 21st Street.

A few local builders are still creating homes like these in the few situations where it’s legal. The problem, they say, isn’t finding people eager to live in smaller homes. The problem is finding lots where it’s legal to let multiple small homes share the cost of the land beneath them.

A four-plex of stacked flats in Woodlawn — currently illegal on almost all Portland residential land.

An 1890 house in Piedmont, moved and hoisted atop a daylight basement accessory unit that doubles as its seismic foundation. The proposed rules would make this legal in more situations.

Portland could make more smaller, cheaper homes like these exist in places where people most want to live by making them legal.

There are a lot of ways to analyze Portland’s residential infill reform plan. But in the end, it’s as simple as that.

Portland for Everyone supports abundant, diverse, affordable housing. This blog is a reported effort to explore ways to achieve those goals. You can learn how to influence the residential infill project here.