Protect your home with proper low roof termination
Here in Washington DC, the circumstances for low slope roof installation are a bit unique because low slope roofs like this are actually a commercial type of material system, yet we have them installed on thousands of residential buildings where there are historic low slope roof homes. One of the unintended consequences of this unique arrangement, here in Washington DC, is that the average installer is of lower quality and lower training and experience than you might find in a market that is exclusively commercial.
As a result of that lower level of quality or training, we often see the same mistakes being made by other roofing contractors, again and again. One of the biggest types of problems that we find is ponding and delamination at the flat roof rear termination. This type of problem leads to leakage and significant cost of repair and remediation. We’ll show some pretty clear examples here. The photos that we’re going to look at were taken just before sunset, a few months ago when the sun was still setting early in the day in our bitter past winter.
Just from the dirt and dust washed off of the roof and then accumulated in the ponding or puddling area at the rear of the roof, you can see a shadow-like dirt line that shows the area of puddling or ponding. When water builds up and stays accumulated in a puddle, on a roof, we refer to that as ponding.
Roofs are generally required, by the manufacturer’s installation instructions, to be installed so that there’s a near-continuous slope or or at least a nearly consistently positive grade from all parts of the roof towards the drain. Here, as you can see in the photo below, is a reverse grade area where the center of that area is deeper than the surrounding areas. Water in that area cannot escape by gravity alone.
Here, in the picture below, you can see that dirt line area in a little bit more clear of a view, and closer. There happens to be one area, right in the middle, longitudely, that runs through the ponding area where it’s a little bit higher. That area looks like a lighter color peninsula that pokes into the ponding area.
That area happens to be coincident with one of the rafters below. That indicates that in the past, as water ponded in this rear area of the roof, water entered through seams or punctures or mislaps or some type of defect and slowly rotted out the sheathing and or framing adjacent to that rafter. Those negative and destructive conditions caused the roof to subside and now as a result water continues building up in that area.
When the previous iteration of roofing was applied, that area should have either been rebuilt, down to the framing below, or a different type of material should have been used to cover the remaining roof structure. This roof membrane system is made or built with a modified bitumen roll material which cannot be installed in any types of ponding conditions like this. Modified bitumen systems happen to be one of the better types of modern low slope single-ply roofing materials available on the market, yet it cannot handle or deal with conditions of ponding or reverse grade and build up of water.
The next problem that we’re going to show is that the end or termination of the membrane is delaminated where the membrane is intended to attach to the substrate metal flashing. That metal flashing in this case is called a drip edge which can be built with a variety different materials, but in this case it’s built with aluminum and is intended to create a physical point of termination where the membrane can be attached. Here though, the membrane has delaminated or separated from that underlying substrate metal.
As I gently touch the material with my finger, the material rolls back because it is loose and unattached to the substrate.
Dirt has already got in between the membrane and the substrate metal and that dirt works both as a decoupler which separates the material from reattaching to the substrate metal and also acts as a moisture retainage type material. Essentially, as it rains and water runs over that rear drip edge that water seeps into the open joint. Once the water around the surface of the roof evaporates in typical weather conditions, that area stays wet because that dirt is absorbent and retains that water for a longer period of time than optimal. That continued excessive hydration breaks down the polymers and other materials surrounding the area of delamination and causes further deterioration and separation.
Here in the next picture below which is zoomed in pretty close, you can see that the material is just loose and delaminated from the substrate. This is a big problem and it’s unfortunately really common here in Washington DC.
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.
