Flat Roofs, Rainwater and Drainage
Posted on January 14, 2010 by Samuel Cheeseman
Pooling rainwater and melting snow can cause serious problems in flat roof buildings. If effective drains are not installed then water damage could shorten the life of a flat roof considerably. There are many kinds of drainage systems available that will effectively remove any excess water as long as they are installed and maintained correctly. If you live in an area which experiences frequent snowfall or storms then you should be very cautious about choosing a flat roof design. Many adverse weather conditions such as heavy rain can damage a flat roof relatively easily.
Angle of a Roof
Many people will ask if a roof can be perfectly flat. It will usually not be a good idea to design a roof which is totally level due to the drainage issues mentioned above. Any roof with a slope of less than 10% in usually considered to be flat. In general water will move very easily but you will need to pitch your roof on at least a small angle otherwise you are just inviting water to form large pools. 
The pitch of a roof is expressed in terms of the number of inches a roof will rise over a length of twelve inches (one foot). A one inch elevation every twelve inches will be written as 1:12. A slope commonly used will be 2:12 and this should prove to be sufficient for most flat roof materials. One quarter of an inch is often the minimum allowed. The International Building Code sets this limit when using asphalt or tar.
Drainage
Flat roof drains will always be necessary to ensure water is allowed to run off of a roof easily. If you are having water related problems then the installation of effective drainage systems in a great way to improve a flat roof. These are located either in the centre of the roof or around the edges. Drains in multiple locations are always a good idea. You should always remember that the roof angle will be important when draining a flat roof. You want to provide the least resistance possible to water which is trying to escape. There are various flat roof drainage systems currently available and the type of roof you currently own will determine the best drainage choice for you. The primary options are traditional drains or scuppers around the edges of the roof and siphons for dealing with water which forms pools. You should research the flat roof drain installations and rainwater outlets on the market which would best suit your property and take into consideration the roof size and pitch, the location of your home, any current problems and of course your budget.
Related posts:
