Roof drain installation should only be attempted by a trained professional.
Whether you own a home or a business with a flat roof (which is something of a misnomer because every roof has a little slope) you will need to choose an option on how to quickly and effectively remove water from your roof.
Standing water can cause problems.
Problems can include the growth of moss and mold and not the least of which is the weight of the water itself. A twenty foot by twenty foot section with one inch of water weighs one ton. Quite frankly, your roof is not designed to support that much additional weight for long periods of time.
There are a few options on how to remove the water from a flat roof.
Gutters and downspouts are very common on residential homes. The water follows the slope of the house to the gutter and down the spout away from the home. This method does, however, require regular maintenance to avoid clogged gutters.
Another method, more common for commercial applications, is scuppers and parapet walls. Again, the water follows the slope to the scupper and the water exits the roof either directly out the scupper or via downspout.
A roof drain is another option.
By using a roof drain, the water is directed through a series of pipes internally. For this reason it is paramount that proper roof drain installation is completed by a professional. If these internal pipes begin to leak, it could lead to extensive damage to the buildings interior.
Also, the point at which the roof drain is connected to the roof can also present the potential for leaks if it is not attached to the roof and sealed properly.
However, a roof drain with a properly sloping roof is an extremely effective means to avoid standing water on your roof.