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UrbanForm Is Better Than 'Back-Of-The-Envelope'


Zoning is so complicated that most of the time a 'back-of-the-envelope' calculation is done to figure out development capacity: i.e., get the base zone FAR and multiply by lot size to get a maximum gross square footage allowed. The problem is that figure can often be wrong.

Depending on the bonuses available, development capacity is often limited by other regulations, such as coverage formulas or special height limits. This is the case in up to 40% of the sites in Portland, based on an analysis of city-wide zoning data by UrbanForm.

By using UrbanForm's AI to apply the correct setbacks, coverage limits, and height limits to every single property, and accounting for available bonuses, we learned those other regulations constrain the development capacity of a site more than the FAR in 40% of the sites in Portland.

Previously, the only way to have known this was to do hours of research and drafting. And that's just for one site.

Below is an example of one site where you can see how the combination of height limit, setbacks, and/or coverage limits puts the total development capacity below the FAR limit.



Here we see an RM4 site with about 10,000 square feet of lot area. The typical base zone FAR for such sites is 4, as shown. If we used a ‘back-of-the-envelope’ calculation, we would conclude that this site would grant 40,000 square feet of development capacity.



But by using the MaxBuild statistics, we see that the development capacity is constrained more than what our ‘back-of-the-envelope’ would have led us to believe initially.

Why is that? By clicking quickly to the Height Limit and Land Detail tabs, we can learn more.



The above information in the Height Limit tab shows a height limit that has been adjusted by the Plan District Overlay to be 45 ft. That height would generally still allow 4 stories of building, so height limit is not the single regulation that would constrain the buildable area to below what the FAR would allow.



It’s here when we click on the Land Detail where we see that UrbanForm has calculated a maximum buildable footprint of 8,099 square feet due to the applicable setbacks. We can see that this limited ground area, in combination with the height limit, would result in a total buildable square footage that is 32,396 square feet—less than the ‘back-of-the-envelope’ FAR would have led us to assume initially.

These calculations are all detailed in the downloadable PDF.



UrbanForm has automated this process for the entire city, allowing anybody to see the gross square footage allowed by FAR compared to the other constraining regulations. Instantly. This ground-breaking information is what we're calling the MaxBuild statistics.

And the MaxBuild Envelope is our feature that allows you to see those height limits and setbacks correctly applied in 3d.



Sign up with an account now at https://pdx.urbanform.us

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