FORSMITH Building Science Consultants (FORSMITH) was tasked with solving the issue of ponding water on the low-slope roof system of a residential complex. Upon investigation, it was determined that the roof had deteriorated severely, and was no longer capable of providing the necessary protection to the building. The roof had inadequate insulation, the seams and flashing had deteriorated, and the roof was covered with sediment and growth. Furthermore, there were insufficient drains with poor flow capacity, and evidence of repeated moisture absorption into the roof assembly.
The main challenge was determining a roof design that would ensure adequate drainage. The roof was equipped with only two drains and installing further drains was not possible. Additionally, sloping the roof to adequately flow towards the drains would not be economically feasible because the roof membrane was showing signs of fatigue in the top membrane layer and the underlying fiberboard was wet. These constraints would be a tough challenge to remediate.
After reviewing the complex roofing conditions, FORSMITH decided that the optimal solution would be a full roof replacement. Simply, the chosen design included the installation of a Protected Membrane Roof Assembly (PMRA), that would drive out the water accumulation. The PMRA works by allowing water to seep under the ballast and insulation to the membrane, creating a buoyancy force that is counteracted by the weight of the ballast on top. The water then travels to the drains. As part of the roof replacement, all deteriorated components were removed, and the new roof was installed to include enough ladder access. By implementing these repairs FORSMITH was able to provide the client with a long-term and durable solution.