What are the types of Flat Roof Material Options?
Various Flat Roof Material Options. The flexibility of a flat roof for certain design limitations is great, but they have some reputation for leaks and repairs. Yes, flat roofs are not flat but have a very slight roof pitch of between 1/4″ to 1/2″ per foot. That is enough slope to drain water but still flat enough to be a problem if not constructed properly.
The nice news is that there are material options for your flat roof beyond traditional hot-mopped built-up roofing that will increase the reliability of the flat roof.
Here is a review of the most common categories of flat roof materials available for your needs:
Modified bitumen roof,
Single-layer membrane roof,
Built-up roof (BUR),
Single Layer Membrane Roof
As you know, the membrane roofing materials are the latest roofing technology and are also a great choice in commercial construction. That is known technically as elastomeric or plastomeric roof membrane (depending on the material), single-ply roofs come in a few varieties including:
PVC (polyvinyl chloride),
EPDM (ethylene propylene diene monomer),
Chlorinated polyethylene and chlorosulfonated polyethylene sheets,
Of all these membrane types EPDM, synthetic rubber is the most common single-ply membrane roof material in both residential and commercial use.
These types of roofs are installed as thin sheet materials 0.030 to 0.060 inches thick and are applied to the roof in a single layer. Being made of synthetic rubber or polymer, they are flexible and elastic and can handle temperature changes and some impact types better than built-up roofs.
Membrane roofing materials are attached in a variety of ways. They can be partially loose laid and held down with river rock ballast (requires roof structure to support the weight) or fully adhered to the roof deck. EPDM and Neoprene roof seams are fastened by adhesive and PVC roof seams are heat or solvent welded.
Modified Bitumen Roofing.
It was developed in the 1960s as a replacement technology for BUR, or built-up roofing, by using the proven technology of BUR but also adding polymer reinforced roof wear layers or cap sheets.
These types of roofs can be installed using different numbers of techniques that are determined by the project’s specific requirements and material specified. This are some of the installation methods:
The most often used polymers are atactic polypropylene (APP) and styrene butadiene styrene (SBS). The polymer used in the cap sheet provides improved elasticity and flexibility in lower temperatures.
Thermoplastic APP sheets, on the other hand, are installed using the torch applied method. SBS cap sheets are usually installed using cold adhesives or hot asphalt tar.
The oldest material of the flat roofing is the built-up roof or BUR. Built-up roofs have solved the low pitch roof problem for ages, a challenge that asphalt shingles could never handle.
Built-up roofs are installed using several layers of a special type of roofing felt that has been asphalt impregnated and embedded in bitumen applied with a hot mop.
A wear surface of finely crushed stone granules is usually applied to the top layer of hot tar to protect the built-up roof assembly from UV light and weather. The hot-applied asphalt or coal tar pitch blends with the bitumen soaked roof felt and creates a monolithic roof membrane. The roof felt/asphalt tar layering is repeated in overlapping layers until the assembly is two to four plies in thickness.