Flat roof homes have particular requirements. Steep sloped roofs rely on gravity to shed water, but flat roofs depend on drains and a waterproof membrane to protect the property below it.
The term ‘flat’ is a little bit misleading because no roof is completely flat. If it were, you’d be living under a small lake on your roof.
“Gradual slope” is a better description of what’s commonly called a flat roof. Gradual slope roofs have at least a 1/4 inch of slope per foot (or more) so water can flow downhill to drains that direct it to the ground.
Flat Roof Types
- Polyurethane Foam: Polyurethane foam is sprayed directly onto the roof. It then “foams up” and turns solid before applying a protective coating. Its also very flexible, so its especially useful for roofs with unusual shapes or angles. Foam has several advantages over other types of flat roofing systems. One of the main ones is protecting against heat so it can cut down your air conditioning bills.
- Built-up Roofs: Many times, built-up roofing is called “hot tar roofing.” Built-up roofs are a very old and time tested method that are made of three or four overlapping layers of asphalt felts that are fused together with hot asphalt. They have to be protected from weather, sunlight and people walking on it by some kind of surface material like gravel, a mineral granule covered top layer, a smooth coat of hot asphalt or some sort of reflective coating.
- Modified Bitumen: Like built-up roofing, modified bitumen is made of reinforced asphalt felts. But the asphalt in the felts have plastic or rubber polymers added to improve elasticity, durability and overall performance. Due to the added polymers, it’s often applied in a single layer with overlapping seams. They then can be attached to the roof with hot asphalt or an adhesive, or by using propane torches to melt the asphalt underside. Some modified bitumen require protective surfacing materials, usually mineral granules or a liquid coating.
- Single Ply: Single ply roofs are made of rubber, plastic or a combination of both. Single ply membranes are applied in a single layer. Installing it is relatively easy: roll out the membrane, heat weld the seams between the sheets, or chemically weld or glue them together. Its then attached to the roof with fasteners, ballast or adhesives.