Post by Catarina Ferreira, AIA
Zoning Regulation changes went into effect in Washington DC in September of 2016 permitting the construction of Accessory Dwelling Units/ADUs(aka Tiny Houses) at the rear of residential properties that meet certain requirements throughout the city, with the exception of zones R-19 and R-20 (Georgetown/Burleith), where density and development in general are closely watched. The same scrutiny applies to Historic Districts, such as Cleveland Park, where we received approval for the conversion of an existing garage into an ADU a few months ago. Yesterday we received approval from the DC Board of Zoning Adjustments for the construction of an ADU on the second floor of an accessory building at the rear of a residential lot in Burleith.
During the public review process for the project, several letters of opposition brought up the height of the structure as a concern. 2nd Stories on Accessory Structures are allowed in R-20 only with a Special Exception, and must meet strict conditions.
We completely agree with the concerned neighbors that breaking down the height of the proposed structure would be crucial. Doing so was a major focus during the design process, as it was a major architectural concern. In addition to respecting the zoning guidelines for maximum height of accessory buildings, we intentionally designed the structure to address the scale concerns from the alley (public) side, and from the private side. The project will be located on a steep lot with a 1 story height different from front (street side) to back (alley side), and the structure had the potential of towering over the main residence's backyard, as well as the neighboring backyards. We did so by breaking down the height of the building visually.
The existing house provided a clue for solving this design dilemma: a disguised 2nd story behind a Mansard roof. Throughout Burleith, this typology is common, and successfully breaks down the height of the modestly scaled row houses that can be found throughout the neighborhood. It also adds architectural interest and scale to those structures.
In the case of our tinier version, the Mansard roof will be a standing seam metal roof, and it is broken by front and back dormers that break down the massing further. These dormers correspond to the main living spaces of the ADU, and allow us a slightly taller height at the front and rear exterior walls of the structure than the 7' prevalent over the service spaces. They are also at the tall ends of an inverted roof, allowing taller windows to be provided and more natural light to penetrate to the interior of the unit, preventing it from feeling cavernous. From the exterior, we made the structure appear shorter without actually making it shorter or losing ceiling height where it counts.