Roofer Mike walks us through a flat roofing project in Miami Springs. Ponding areas, the use of tapered insulation and the difference between GAF Ruberoid and “cap sheet” are discussed.
In Miami Springs many homes have had additions built with flat roofing which can get pretty hot in summer if the ceiling is not sufficiently insulated. Such was the case with this roof and the owner wisely chose to include insulation in the roofing specifications. There were also a couple of ponding areas to address and since both were fairly close to the eave we included tapered insulation at the perimeter.
According to Miami-Dade County any standing water which does not evaporate after 48 hours is considered excessive ponding. I have an issue with this standard as a roof could be under water for considerably longer during rainy season when daily thunderstorms are common. A flat roof with a ponding area which takes 36 hours to completely dry could be submerged for many days at a time. I like the idea of the county’s standard but we like to design our flat roofs so they dry completely in one afternoon. This ensures there will be no ‘algae farms” developing which feed on the calcium carbonate in granulated systems and can lead to a premature loss of granules.
The use of tapered insulation is an excellent way to deal with ponding. Here the eaves were slightly elevated, causing rainwater to gather. We installed 1 1/2” EnergyGuard Composite Board Roof Insulation to within 3′ of the eaves. We usually use a minimum of 1 1/2” of insulation to ensure an effective R-Value. 1 1/2” – 0” X 12” x 4’ tapered edge was then installed. This sloped the insulation from 1 1/2” thick to 0 in a one foot span, leaving a one foot flat area without insulation at the edge. Two layers of GAF #75 Base Sheet and the insulation were simultaneously attached with 3” Drill-Tec plates and #12 screws in a pattern conforming to Roofing Application Standard 128 and its minimum uplift requirements. This flat roof is not going anywhere. 26 gauge galvanized flashings were then installed and primed for good adhesion.
Torching the Ruberoid Torch Granule cap is my favorite part of the job. I’d torch roofs for my friends and family for free if I hit the Lotto – really!! Tearing the old roof off is their problem . My main guy torched most of this one but I had to jump in and cook a few rolls just to stay sharp.