If you feel capable of doing it yourself, be sure to follow the safety guidelines discussed below. The type of roof you have largely depends on what is most popular and practical in your part of the country, and on when your house was built. Another important aspect of roofing structure is the extent of a roof's steepness or incline. Referred to either by its slope, pitch or angle, this factor determines the type of roofing material that may or may not properly be used. A roof with little or no slope is called a low slope or flat roof.
Water tends to lay in pools, and debris accumulates on flat roofs because of their lack of run-off.
Clogged drains running through the building may leak and result in internal damage. Since water expands 700 times in volume from the liquid state to the vapor state, any moisture penetration into the felt layers of a built-up roof can cause bubbles, ripples and delamination of the system. This often results from the flat roof's accumulation and longer retention of rainwater, ice and snow. Flat roofs also chronically suffer from poor ventilation. As a result of condensation, or in the event of leaks through the bituminous coating of the built-up roof, poor ventilation can lead to decay or delamination of the plywood sheathing.