Carriage Houses: Horizontal Pop-ups?

Summary: I believe DC's Historic Preservation Review Board (HPRB) is encouraging, when possible, those wishing to expand homes in historic districts to forego pop-ups in favor of constructing new "carriage house-like" buildings at the rear of their properties. Plan for these new buildings often trigger a review by DC's Board of Zoning Adjustment (BZA), as the old and new buildings combined take up a greater percentage of the lot than is permitted by law. The BZA seems to be willing to go along with these rear additions. The small number that have been approved so far have not changed the profile or density of historic districts. If the trend continues, there may be negative consequences.

Homeowner a no-show at meeting

On Monday, July 21, the Design Review Committee of Advisory Neighborhood Commission (ANC) 1B/U Street had a meeting. The only significant item on the agenda concerned 919 T Street NW. The owner sought ANC endorsement on a request to the BZA for a special exception to permit an addition at the rear of the property. The addition, the meeting agenda said, would serve as the primary residence of the owner.

919 T Street, as seen from 9-1/2 Street

There was a quorum of committee members, but owner did not show up. The chair of the committee called the owner. There was no answer. As there was no other business, the meeting disbanded. It is unclear whether the owner will be able to arrange another hearing with the committee and then with the ANC before a scheduled BZA hearing on September 9.

919 T Street is located in the U Street Historic District, so the owners got approval from the HPRB for their proposed new rear structure. The HPRB report characterizes the proposed new structure as a "two-story carriage house-like addition at the alley". (The alley is also known at "9-1/2 Street", and has 6-8 homes on it.)

The footprint of the proposed new building, combined with that of the original building, put the lot over the limit for "lot occupancy", which is why the project has to go before the BZA.

A pattern emerging?

This is the third "carriage house-like" rear structure that I've seen HPRB approve in the last two months -- see SALM blog posts for June 12 and May 30. (I also reported on one last October.) The properties are located in a variety of ANCs (1B/U Street, 2B/Dupont Circle, and 6E/Shaw) and historic districts.

In each of these cases, HPRB-approved rear structures (sometimes designed to look like long-demolished rear carriage houses) put the homeowner over the lot occupancy threshold.

In the cases reported on June 12 and May 30, the homeowner had been strongly discouraged by HPRB from pursuing a pop-up addition before receiving an approval for a rear addition. And, also in both of these cases, the homeowners subsequently received the zoning permission they sought from the BZA.

I don't know how many instances constitutes a trend, but there seems to be a pattern in HPRB, and subsequent BZA, approvals: more vertical living space -- no; more horizontal living space -- OK.

HPRB can be the good guy

This is probably a clever move for HPRB. Instead of being the agency that always says "no", they can be the agency that gives viable alternatives. It is then up to the BZA to be the bad guy if it turns down homeowners on the basis of lot occupancy, which could be perceived as an abstract, unimportant technicality.

So far, it seems like BZA is not inclined to be the bad guy, as evidenced by their approvals of lot occupancy exceptions.

Lot occupancy restrictions are, presumably, there for a reason. One DC Zoning Commission document from 2010 (21-page .doc download here) says the intent of lot occupancy restrictions to preserve adequate light and air to building residents. Another function is as a guard against excessive density. Yet more carriage houses (or alternately "out buildings" or "mother-in-law houses") on the rears of properties will surely increase density, and affect the light and air in the immediate area. Like popups, no one will mind the first carriage-house-like rear addition on a property, or maybe even the second. But what will happen when many houses on the block want them? Will the BZA continue to approve these requests?

More lot occupancy = more water runoff

More rear lot additions will also increase the amount of land in historic districts which is impervious to rainwater. DC Water is so concerned about impervious areas that it has instituted an "impervious area charge" on all customers. The impervious area charge is the single biggest component of this year's proposed 13 percent increase in water rate -- see SALM blog post of April 29.

The charge is based on how much impervious-to-water surfaces (such as rooftops, paved driveways, patios, and parking lots) a homeowner has on his or her property. Impervious areas contribute to groundwater runoff entering the District's sewer system. Popups, which by definition sit on top of existing buildings, do not increase the amount of impervious area on a lot.

More rear structures mean greater lot occupancy. Greater lot occupancy means more impervious area. More impervious area means more water runoff. More water runoff means more wear and tear on the sewer system, and also greater possibility of flooding during major rain events or hurricanes.

Solving one problem, creating another?

A few additional residential spaces by themselves are unlikely to cause more flooding, of course. But if a quick trip through the city bureaucracy becomes the norm for "carriage houses" and similar rear structures, the cumulative effect of hundreds of one- and two-story rear additions could be significant.

This may be a case of government agencies focused narrowly on their own briefs, to the exclusion of other considerations. HPRB's brief is the appearance of the exterior of properties in historic districts. The BZA's is to identify and prevent inappropriate and unsafe land uses. The knock-on effects of increased density are not an immediate concern to either body.

Will there be a time when we starting thinking that an attempt to control one problem (pop-ups) has opened the door to others?

See the latest HPRB document on 919 T Street here.

Documents concerning the request by the owners of 919 T Street for a special exception can be viewed by going to the BZA's Interactive Zoning Information System and entering case number 18810 in the search bar.