Image by Gabriele Diwald licensed under Creative Commons.

The DC Office of Planning (OP) wants to tweak an important rule in how the city's zoning code measures the size of buildings. The city makes a distinction between the floors that sit partially below grade when deciding the size of the buildings: they are either “cellars” or “basements." Basements "count" towards various important zoning restrictions, while cellars don't. 

However, this rule is controversial and has led to a few legal challenges, and now the city is trying to clarify the code. That clarification is good, as long as it makes the code more flexible and doesn't constitute a citywide downzoning, which means a reduction of density and potentially fewer homes. Unfortunately, the full impact is not clear. 

Cellars and basements are not the same

Here's how it works. Basement space counts towards the Gross Floor Area measurement, or the sum of a building’s square feet that gets divided by the area of the lot to create the “Floor Area Ratio." Basements also count toward the number of stories a building can have, and both the Gross Floor Area and number of stories are regulated by zoning.

Cellars, though, count towards neither, supposedly because they are hidden enough to not affect the “bulk,” or perceived size, of a building. This exception is a defining feature of buildings in space-constrained DC, and it has permitted a significant amount of less expensive housing. However, that doesn’t mean this rule isn’t controversial.   

Image by Elvert Barnes licensed under Creative Commons.

The OP's proposed changes come at the heels of a few challenges to how the city interprets the rule. Most relevant were objections to a rowhouse conversion at 1514 Q Street NW. A new apartment building at 5333 Connecticut Avenue NW faced similar criticism. 

Both of these projects were approved under the city’s zoning code that lasted from 1958 to 2016. Changes made in the 2016 code update made the measurement more transparent, but the cases highlighted some other inadequacies. So the OP wants to change three main things: how “cellar” and “basement” spaces are measured, what kind of ground counts for measuring height, and the definition of a “habitable room.”

It’s only a few words, but they affect every building in DC. That's a big impact. If done wrong, buildings that haven't changed physically could legally become a story taller and increase in size. That would reduce the amount of density from what is now allowed, and decrease housing potential with few benefits.

What does it mean to be "habitable"?

The simplest change is the definition of “habitable room.” The Q Street case hinged on a claim that a “habitable room” could not be a cellar because at some points the zoning code used the term “habitable room” to exclude attics and cellars.

The case failed because of a technicality, but it looked shaky before then: courts and the zoning commission had long interpreted the term “habitable room” as only relevant for integrating residential spaces into commercial districts. Thousands of cellar apartments had been constructed and occupied for years with no ill effect. Being in a cellar doesn't get developers out of following the building code, after all.

Either way, the text was not clear, so OP’s proposed fix removes the exceptions to clarify that the definition of cellar is about bulk and not whether a space is livable.

The city also wants to change a measurement

The second change is more substantial. OP wants to center the difference between cellar and basement on the “ground floor,” which the code defines as “the floor level nearest to and above the adjacent finished grade.” They also propose moving the definition of gross floor area of the height of buildings out of definitions and into a section of general rules, which are interpreted more strictly.

Contraption used to measure ceiling height at 1514 Q Street NW. Image by the Office of Zoning.

Under the 1958 code, the relevant measurement was to the bottom of a ceiling, which allowed developers to put in a new ceiling just under the limit and therefore create a cellar. The Q street conversion did this. 

Under the code adopted in 2016, the code shifted away from ceiling height, but used three different measuring rules: one for defining cellars, and two separate measurements for measuring gross floor area (GFA) in attached and freestanding buildings. OP now wants to use one measurement: five feet from grade to ground floor. The ceiling of the bottom floor no longer matters, as it currently does for defining cellars. 

Shifting ground

The third change is the most significant. It attempts to clamp down on developers altering the grade of a building’s site to achieve the cellar measurement. In the 1958 and 2016 codes, cellar height was measured from finished grade.

The planning office’s change makes the elevation either that of the final landscaping or of the grade that has existed for more than two years on the site, whichever is lower. They also add the same pick-the-lower rule to all other height measurements, which were previously different.

Confusingly, the zoning code calls the existing terrain “natural grade,” although it encompasses anything from before 2015. It also bans “berms” — a raised strip of land — from being used to cheat on height, but leaves the term vaguely defined. 

How this impacts housing density

It makes sense for codes to be as clear as possible, so the changes to cellar measurement and habitable rooms seem reasonable and preserve the status quo.

Some people have expressed concern that the new rules of cellar measurement would make it harder to add housing by reducing the number of less expensive cellar apartments. However, that impact seems minimal. For a new building, the shift from a ceiling to a floor is not likely a big deal: the thickness of a ceiling and floor can be as little as nine inches in a new concrete building.

The floor area changes wouldn’t stop conversion of cellar spaces into apartments. The cellar rule regulates bulk, and an existing building’s bulk is already there. At worst, the bulk becomes “nonconforming.” As long as any alterations do not increase the bulk beyond what’s allowed, rearrangement inside is permitted.

The changes would affect additions to existing buildings, with ground floors five feet above existing grade. This is what happened on Q Street: the site had leftover floor area if the bottom level was a cellar. If it was a basement, the building would not have nearly as much surplus floor area, and the addition would have been in violation.

Image by Jean Flanagan licensed under Creative Commons.

Changes should be proactive, not reactive

The thing is, it's not clear how many buildings would be affected, so we don't know if this would reduce density across the city or not. As of writing, OP has not submitted anything to analyze these changes, other than noting this will reduce the amount of interpretation and risk of challenges to rulings.

In general, this proposal seems to be reacting to one issue and fixing a loophole without putting forward a proactive vision for how the city should look. How could the zoning be putting partially-buried space to use, or improving the continuity of the public right-of-way? The fix does not seem to consider that. And unlike in the 2016 revision process, OP has not publicly compared the proposed rules to those used by other cities. 

Personally, I am concerned about the changes on picking landscape grade. I think this makes the code too prescriptive and discourages inventive landscaping in order to stop a specific form of abuse. It's good the city is trying to keep things simple, but a code written by reacting to loopholes risks creating a rigid and counterproductive system that leaves the city worse off.

Bottom line: New buildings won't change much, but it may well get harder to convert existing rowhouses into multi-unit buildings. When those conversions do happen, some may be a floor shorter with commensurately fewer units.