There are four main types of flat roof:
Built-up roofing (BUR), or tar and gravel flat roofing, is comprised of a waterproof base layer, multiple layers of roofing felt laminated together with bitumen, and a layer of gravel for weight and UV protection.
A modified bitumen flat roof is similar to a BUR roof, but with added reinforcements to give it a rubber-like property. There are two basic types: torch down and peel-and-stick.
A rubber roof, or EPDM flat roof, is a synthetic rubber very similar to that of an inner tube. It is applied in thick strips with either a liquid adhesive or a specially formulated tape.
A PVC or vinyl roof is similar to the thick plastic pipes used for drainage, but with additional plasticizers and stabilizers. It is form of membrane flat roofing that is heat-welded at the seams.
Applying a modified bitumen torch on flat roof | @ iStockphoto.com / deepblue4u
Problems with a Flat Roof
The main culprits causing a flat roof replacement are poorly secured or damaged flashing, cracks or bubbles and ponding water. Bad flashing, cracks and bubbles are like having a hole in your umbrella. Ponding lasting more than 48 hours after rainfall can indicate a poorly installed flat roof, and has the added effect of increasing the effects of UV rays.
BUR flat roofing is prone to leakage, and the source can be difficult to find as water can travel many feet from one defect layer to a defect in another. Gravel can clog gutters, and exposed tar paper will weaken the structure, ensuring an imminent replacement.
Inspecting Your Flat Roof
Regular inspection can prevent replacing your roof early. Walk the entire surface of the roof, paying attention to how to feels underfoot. A soft or squishy area could indicate wet or damaged insulation. Look for cracks and blisters on your flat roof, as well as ponding water.
For a BUR flat roof, look for areas where gravel is missing and tar paper is exposed. If there are areas where gravel has piled up, use a stiff broom to brush the gravel away, and evaluate the tar paper below.
As with all roofs, take a peek in your attic to check for water damage.
When Your Roof May Need Replacing
You should contact a professional for an assessment if you notice any cracks, bubbles, damaged flashing or water damage in the attic. They can tell you if the problem can be patched up or if you need a full roof replacement.
This is important as the problem may not be cosmetic, and has likely affected much more than the eye can see.