This post originally appeared on Orphan Road.

Several Roosevelt neighborhood plan supporters are claiming that Roosevelt’s new zoning will triple the existing population within 1/2 mile of the new rail station.  At first I was tricked – triple the zoning is at least a win for Seattle, and probably as much zoning as I would have asked them for.  But some of the numbers didn’t quite make sense. 

Architect John H. Adams ran a density study, which is where these numbers come from.  But even though that study seems to indicate a tripling of density, it still has numbers like 1,000 new units.  Can there really only be 333 units currently?  And then I saw it – Mr. Adams is comparing current population with future zoning – not current zoning vs. future zoning.  Reading into his study a bit, it’s clear that the new zoning only increases potiential units by 10%.

Why this matters is that we clearly won’t get anything close to the number listed in future zoning.  The only way to do that is to bulldoze the entire area to the ground, and build up a maximum number of units on every single property.  Except in major urban renewal projects (which is clearly not called for here), this doesn’t happen.  How development works is that over time inefficient buidings (say, a 1 story building in a 6 story zone) become worth less than the potential profit that comes by building up.  That new building still rarely comes anywhere close to the maximum number of units, because as a new building it’s generally marketed as high-end and includes large units.  Over time, most of the buildings that are widely different than their potential height are replaced.  But what about the 4-story units in a 6-story zone?  It would take a very high price per unit or very low construction cost to make money on bulldozing that building, since (profit) = (value of additional units) – (construction cost) and you aren’t adding that many new units.  So the end result of upzoning by 10% isn’t a tripling of units – it’s probably an increase by about 10%.

Ok, but how much upzoning does the Roosevelt area need?  I’d argue that Seattle needs to at least match WA’s rate of growth if we’re able to even keep up with sprawl, much less reduce it.  That means every single neighborhood is due for at least a doubling of their current zoned capacity, since WA’s population has doubled since the mid 70’s while our population has stayed roughly constant.  And that’s ignoring the fact that this is a light rail station, which should have a large potential for growth.  But doubling the zoned capacity should be an absolute minimum.