A Built Up Roof (cap sheet) is a tried and true system that has been used for many years in the roofing industry in Miami. It consists of several layers of felts and hot asphalt hence the name “Built Up Roof”. The base layer is a #75 felt which is rolled out over the deck and mechanically adhered using 1 5/8” tin caps and a 1 ¼” ring shank nail using a nailing pattern determined by the height of the building and the deck type. Once this phase is completed 3-4 layers of fiberglass felt are rolled out and adhered using hot asphalt mopped over the surface between each layer. This fiberglass section is the “roof”. It is what waterproofs the roof, but the fiberglass is susceptible to the sun and requires an additional coating or layer to protect it from the sun. The old way to achieve this was to paint the roof with an aluminum coating which needs to be maintained on a regular basis as the aluminum paint dries out and flakes off over time. In more recent times the advent of the cap sheet helped alleviate this maintenance and provides a longer term “sun-block” for the roof. The cap sheet consists of an asphalt felt covered in mineral granules to insulate the paper. There are essentially two types of cap sheet widely used, regular cap sheet and rubber modified cap sheet.
The built up roof system although reliable has proven to be vulnerable in many instances, especially during hot South Florida summers. It charges a large amount of heat throughout the day making the roof system exceed temperatures of 180 degrees Fahrenheit on a 90 degree, turning buildings in to energy vampires. If a BUR system is exposed to ponding water exceeding 48 hours it is susceptible to being damaged. The hot South Florida sun along with its biologically conducive environment allows for the growth of bacteria, algae, fungus, and molds to decompose the organic asphalt and paper. This system also comes short in terms of its installation process as it involves a very dangerous labor intensive installation. This method carries great liability as it amplifies Murphy’s Law. A hot tar kettle is dragged to and from the job site, once the tar kettle is at the job site it is turned on and runs at about 550 degrees Fahrenheit, solid blocks of asphalt are put in to the kettle to get it to a liquid state. This is then poured on to a smaller kettle which then has to be transported up on to the roof by hand. As the tar is spread on to the roof small drops of the asphalt are splashed up in to the air and it lands on the surrounding areas leaving stains and damaging property, all this while it is emitting toxic fumes which the installers inhale, pollutes the environment, and the smell lingers as the material cures over the following days and weeks.
Stay Tuned for Part 2 of Flat Roofing in Miami