Why front porch roofs need timely attention and care
Today, we’re looking at front porch roofs, but not just not just looking at one specific porch roof, a series of porch roofs that are basically interconnected from one house to the next in a row of historic buildings. These couple of roofs happened to be next to the one that we were working on when we replaced the existing roof. As you can see in the pictures below, the existing roof was a modified bitumen single ply membrane roof system.
The old / existing roofs were installed many years ago and at this point are way beyond its original intended lifespan. Even without knowing the exact year that it was installed we can see that there is damage and deterioration and defects that go all the way back to the time of that original installation.
Since most of these buildings were built over 100 years ago, the porch roof was also built at that same time together with the house. The original or earliest actual original porch roof was built much earlier, but the modified bitumen roof was installed directly on top of those materials about 20 to 30 years ago. We’re just guessing that time range though because we don’t know for sure. We know that modified bitumen roof materials have only been used in high frequency here in Washington DC up to about 40 years ago and the majority of them were installed between that time. That ranges from about 20 to 30 years ago.
The particular signs that indicate there are problems, jump out right away when looking at the photo below. You can see that there is a dirtier area around the center of the roof, near the front edge. That area of dirt deposits indicates that there is an area of ponding or puddling. Essentially during almost any types of rain events or precipitation, water will pond up at that area because it’s built lower than the surrounding areas. In most cases, where there are ponding areas inside of the rear termination of a typical flat roof on the main part of a building, it’s a problem.
Here though, it’s a little bit different because although it’s still a problem, it’s not the type of problem you find on those roofs. Typical loose laid roofs over the main part of a historic building were intended to drain over the rear termination. Normally, that rear termination is built with a drip edge and that drip edge should be the lowest part of the roof system.
Even though that’s the way they’re intended to be built, we often find there are mistakes in installation, those mistakes often don’t go all the way back to the original installation, they’re normally a type of installation defect that happens when the second or third or even fourth roof is applied in sequence after the original construction.
This problem with the elevation of the rear termination happens, generally, because at the time of re-roofing, it’s intended and beneficial to remove the rear termination completely and adjust the gutter accordingly. At that time a new drip edge should be installed at the height of the planar sheathing or decking on top of the roof rafters. Often, as a shortcut, people doing the roofing work, particularly if they’re not high quality contractors, like ourselves, will roof right over the old termination, even when they remove the remainder of the roof system which creates a bit of a buildup at that area. That then leads to ponding and a residual build up of water.
In the next picture below, you can see that the seam of a strip of membrane laid like stristin flashing to the drip edge is also delaminated from the substrate. This is a big problem because water builds up in that specific area.
For pounding water to build up at a location where it is coincident with a seam, it’s significantly more problematic because seems have a tendency to deteriorate and open when they are submerged in water for extended periods of time which is the exact case described when there’s ponding. Ponding is dictated or imposed by the configuration of the plane or contour of the roof. Here, the seam needs to be repaired and the contour should be fixed, but changing the contour is particularly problematic. It requires extensive rework of the substrate which means removal of at least a portion of the roof system, just for that repair.
We provide this information here on our blog, and our website, to help our customers and future clients, and 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. Our company specializes in flat roofing here in Washington DC and we’re happy to help building owners of almost all types.
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. We are happy to help and at least talk through options.
