Today we’re taking a look at a flat roof, similar to many of the flat roofs we see around the Washington DC neighborhoods like Capitol Hill and Dupont Circle, but these particular row homes were built a little bit differently and it’s a bit of a unique circumstance. They don’t have an actual parapet between side by side built row homes.
Instead and applied type parapet has been built on top of the framed roofing and a coping metal spans on top of that framed element with the individual roof systems terminating underneath of that coping metal.
For several specific types of elements like penetrations through the roof membrane to exhaust air or plumbing vents, the building code requires and recommends minimum heights depending on the local area and the typical snow loads. This original building may have been built with all row homes as part of one construction and without a parapet rising above the roof systems.
Many of our older, classic row homes were built before modern building codes, with much shorter parapet heights, typically only around 8 inches high.
A parapet has several additional distinct purposeful functions. Three of the most important functions follow:
- Between joined buildings, the parapet provides a location for each distinct building roof system to terminate.
- A parapet serves as a fire barrier between adjoining buildings or sections of a building to contain the spread of fire.
- Lastly, a parapet can provide a raised surface for mounting rooftop equipment, such as HVAC units, antennas, or solar panels, while keeping them set back from the roof edge. BUT, it is very important the bearing of materials or equipment does NOT damage oflr penetrate the parapet as is so often done by photovoltaic solar panel installers.
In the case of historic city row homes, the roof of one building is attached to the roof of the next building but the parapet provides a place of demarcation and separation where the roof membrane can terminate. At the front and back of the buildings where buildings are not connected to an additional or separate building, it’s easier to make a termination because the roof can terminate independently going from the horizontal position downward over the edge of the building. At these locations there is usually a fascia board to which a drip edge or gravel stop can be installed and the roof membrane, on the other side of the termination, can be secured. In many cases, the historic row homes today were built as one building or built differently and not actually separate the way they are broken up and split into smaller residences today.
A parapet acts as an effective fire barrier by creating a continuous vertical barrier that extends above the roofline. Its construction, using non-combustible and fire-resistant materials, such as historic brick masonry, prevents or deters the instantaneous spread of flames and embers from one roof to another. The height of the parapet plays a part or role, as taller parapets create a more substantial obstacle to the horizontal propagation of fire. Parapets subdivide the roof area into smaller compartments or sections, ensuring that if a fire originates in one section, the parapet contains the blaze within that compartment, averting its spread to neighboring sections or buildings.
Parapets, when well built can also deter the passage of flames, smoke, and hot gasses in the demising wall areas below the roof. By building a continuous, fire-resistant vertical barrier between structures or building segments, parapets significantly impede the proliferation of fire, affording more time time to respond and mitigate the situation, ultimately minimizing the risk of extensive damage to adjacent properties.
For these historic row home neighborhoods, the building codes today allow grandfathered provisions to preserve the original architectural character, rather than enforcing new parapet height minimums retroactively.
So for historic districts in DC, while new construction must meet the 30-inch code, the existing iconic short parapets on centuries-old row homes are often a grandfathered condition and allowed as part of the area’s architectural history, despite providing relatively minimal fire separation compared to modern standards or even the ones built at 8” in height.
Too often, we see solar panel installers in Washington DC drill and bolt their purlins or aluminum beams directly through the metal coping on top of the roof parapet. This is not allowed by the building code and should be strongly or seriously avoided. This type of improper installation relies on almost nothing more than just sealants to prevent leakage of water from the top of the parapet through the coping and down into the building. The sealants, alone, are a very weak defense from the exterior elements.
We recommend every building owner in DC who values the longevity of their roof (and their investments) and building use a contractor who values the simple and important principles of proper roof construction like Dupont Roofing DC. Learn more about our company and the proper techniques of working with roofing on historic buildings in Washington DC here on our blog at DupontRoofingDC.com, and you can call us at (202) 840-8698 and email us at dupontroofingdc@gmail.com.
