Roof Drainage Issues? How to Determine Your Options

Posted on: 26 October 2016


Have you noticed some drainage issues on your roof recently? This could be because of improperly sized or installed roof drains. These types of fitment come in a variety of different sizes and shapes and must be chosen according to the specific building and roof that they're going to be installed on. If you think that you may need repairs or replacement, what do you need to consider?

Factors to Take into Account

Firstly, its important that the drains be spaced equally around the perimeter of the roof at its lowest point, or in any position where water seems to accumulate. In order to determine how many drains you need and their size, you have to calculate the entire surface area of the roof that will channel rainwater towards the drains. You also need to know what the average rainfall rate is for your home. You can get this information from your local authority.

Then, you have to determine the size of the drainpipes, which are also called leaders. This will be determined according to the amount of rain water that each pipe has entering its specific 'catchment' area. Usually, the drainpipe manufacturer can help you determine this calculation.

Other information you need to consider when selecting the proper type of roof drain is the pitch of the roof itself and the rate of drainage (which will vary according to the pitch) and the average volume of rainfall. You need to consult your local building code to determine whether there are any overflow requirements stipulated.

Talk to your roofing contractor about the roof load. This is a factor that is based on the amount of water that the roof can actually hold should the drains be obstructed. This is an important metric as it determines the overall stability of the roof.

Siphonic Options

It may be advisable for you to consider the fitment of a siphonic roof water drain. This type of drain essentially vacuums water from the roof at very high velocity as compared to conventional drains. The benefit here is that a smaller number of roof drains will be required, and they are all typically connected to one drainpipe. While this is a far more efficient system and is very smooth and efficient, it usually requires much less maintenance going forward. The siphonic drain is costlier than its conventional counterpart, but it is much more flexible when it comes to design and fitment.