65%, 57%, 35%: how much Seattle land is zoned single family really?

It's a number that gets bandied about a lot. Depending on who is involved in the conversation you will have angry repudiations and corrections of that number. "Well, actually ..." followed by a claim of a wildly different number. I happened upon Rezone Seattle today which pointed me at page 421 in the appendices (pdf) of Seattle's Comprehensive Plan. That page has the end of a very long data table that breaks out the number of acres in different sub-regions of Seattle by their zoning. Since it's the end of the table it has the total acres per zoning type catalogued. Here's a picture:

Or so I thought. Then I re-read the data table and realized it was acres currently built to each use which would be pretty inaccurate to the question I'm trying to answer. There's a lot of grandfathered in multifamily use in our single family zones: think duplex, triplexes and even 8 and 16 and higher multi-unit apartment buildings. The catch is if you bought a property with a duplex on it and tore the duplex down, you might not be allowed to build anything but a single family home on it.

Anyway, I kept searching to find the right numbers: number of acres zoned to each category of use. I quickly found a 2015 zoning capacity report. That seems close enough for these purposes, so let's pull some numbers out. Zones that I believe allow residential are in bold (you can lookup the zoning designations in the SMC). Note that a bold zone doesn't mean it's typical for a majority or even a large fraction of acres in that zone to actually have housing. This is probably obvious if you think about neighborhood commercial which is often along main roads in the commercial strip of a neighborhood: most of the buildings have little to no residential use.

This table doesn't call out right of way acres, but if we take those (14,153) from the first document, add them to the total acres here, we get 51,037 acres total, which even leaving aside parks (not sure how to add that in), that means we have about a quarter of our land devoted to right of way. That is, cars. When you consider how many unnecessarily wide and multilane roads there are, that dedication to roads is very suspicious. Anyway, moving on.

Now, you'll note in the original data table there's a column "Net Acres" and a column "Open Space" which perhaps immediately tells you why we have dueling numbers. Counting up the number of acres zoned for single family is perhaps not terribly controversial. There are only so many single family designations and it's pretty clear which parcels are zoned that way. The confusion in numbers is thus going to be around the denominator. Just how many acres are we going to divide 24,699 into for our percentage? Some denominator options:

• All acres in Seattle. That's 53,151 acres according to the first document found.
• Net acres. That is, all acres not part of a right of way or 38,998 acres (again first document, though one doc is from 2017 and the other 2015 so this could get weird). This would include open space (parks) and parking and other uses like that.
• All acres that have some kind of zoning designation in the 2015 pdf. That is 36,884.
• All acres that could have housing built on them. That would include single family, multifamily and some commercial/mixed-use. A lot of commercial acres aren't going to have housing on them of course, but we'll just take the full number. That total is 30,776 acres. Some of the major institutions & public uses land might have housing on it (e.g. the University of Washington), but I'm guessing that the number of acres is relatively small. In any case, those acres aren't available to build housing available to anyone. That number also includes all the downtown zoning where it allows residential but it's heavily dominated by non-residential uses on many blocks. It's also all mostly built up so it's not like we're going to build more housing there. Nonetheless, that's one option for a denominator.
• All acres zoned for reasonably buildable housing options. That is, ignore the  downtown weird zones, and only look at the normal LR, MR, HR and all the single family. That number would be 28,621 acres.

We could get more complicated and optionally include parks in some of these denominators, but let's just use these possible denominators. What percentage of land is subject to single family zoning by each category?

• All acres: 46.5%
• Net acres: 63.3%
• Zoned acres: 67.0%
• Housing acres: 80.3%
• Not-downtown-weird-zoning housing acres: 86.3%

There are some pretty big caveats on these numbers so don't quote them for anything. The biggest one is I'm using two documents from two different years reporting somewhat different things. I don't think Seattle acquired, officially, thousands of acres between these two years so I don't think the total acres is too far off, but I could be wrong. We also did do some upzones in some of the urban villages and downtown, but that mostly just changed various mixed and multi-family uses into other mixed and multi-family uses: not many acres would have flipped from single family to multi-family. I just wanted to give a ballpark, so I'm not too worried about these caveats.

What is eminently clear is that a lot of Seattle is zoned for single family uses only. That is, land uses that exclude any family that can't afford a detached single family home, which is the most expensive form of housing. Much of the single family zoning – over a third – requires lot sizes greater than 5000 square feet, only deepening the economic exclusion. There are only 6077 acres of land zoned for any king of multi-family residential. For every acre of multi-family – and it includes all those weird mixed zones that are often not built with much housing and what housing is there is often very expensive – there are 4 acres of single family zoned land. Four acres of single family homes to one acre of dense, affordable homes. No matter how you rearrange the numbers, far too much of Seattle is zoned to non-dense, suburban use.