Flat Roof Drainage The Basics…

Posted by judy


A standard sloping pitched roof can generally be expected to last more than a hundred years without needing to be replaced, but the life expectancy of a flat roof tends to be quite a bit shorter – and often the covering may need to be replaced after 20 or even 10 years.

However, the initial building cost will be lower, and, of course, that is one of the key advantages of flat roofs. That’s because fewer and lighter materials can be used.

You’ll often find flat roofs used on purpose-built apartment blocks or for garages or extensions, rather than whole structures for houses or bungalows.

Equally, there are sometimes design arguments – for example when putting a roof over a small gap between buildings which are already in place.

There are a number of coverings you can choose from, and you may also need to take the extra need for insulation into account when constructing a flat roof or having one put in place.


Flat roof drainage is one of the single biggest problems you are likely to encounter when you go for this kind of covering.

Here are some tips to help:

  • It may sound odd, but, actually, a flat roof shouldn’t be 100% flat! In fact, its design should always include a fall to drain off water. Even where there are small deflections, the better the roof drains, the less likely it will be that you will get ponding problems.
  • The fall should always be near the spot where the roof drains, either by a parapet gutter, eave or other drainage outlet.
  • Inspect your roof regularly (ideally yearly) to check for water still covering it or a blocked eaves gutter which can cause water to pour down the wall below, and other problems, before they become too serious. The good news is that, with regular inspection, many issues can be dealt with in a speedy, straightforward way.
  • When inspecting, check for built up grit and other debris in a pond on a flat roof. It may just grow algae or weed which can weaken the covering of the roof.
  • A flat roof’s wet and dry sections will behave differently, and there can be stress cracks where the two areas meet, so this point is especially vulnerable to potential damage.
  • Finally, remember to protect mineral felt, commonly used as a flat roof covering, from the potentially harmful effects of the sun’s rays with solar reflective paint or by placing chippings on top.

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