Are you coping with the rain ?

by Doug Basen- Local Authority Building Control

So what has this got to do with us from a professional angle, you ask?

Well, H3 Rainwater Drainage simply tells us that ‘Adequate provision shall be made for rainwater to be carried from the roof of the building’. The guidance to H3 says it must carry the flow of rainwater from the roof to an outfall with minimal risk of blockage and it must be accessible for clearing blockages.

Various tables in H3 Section 1 advise on maximum areas of roof that can drain into specified gutter sizes and gutter and outlet size. But what it doesn’t tell us is how to deal with the different sorts of anti-blocking gutter systems that may be incorporated into the gutter that won’t impede carrying capacity.

Some housing developers are choosing to install products in the gutter at the time of development often as a result of nearby trees. Unless carefully chosen, they can unwittingly be a cause of blockage. BS EN 12056-3:2000 Clause 7.3.3. states ‘the reduction in outlet capacity due to strainers being installed shall be taken into consideration.’ It therefore follows we need to pay particular attention to what if any means of debris prevention is proposed at design stage, this applying equally to outlet design.

For those amongst us who are not too familiar with the various products sold to deal with gutter blockages here are a few examples.

  • The first is a system that incorporates filling the gutter with different types of foam, fibres, rubber or acrylics.
  • The second is known as hedgehog gutter system, which is self-explanatory when you see the image.
  • A third is a product known as gutter-clear, which is positioned above the gutter and does not affect flow capacity of the gutter.

It would seem the first two examples will immediately cause a reduction in flow capacity as a direct result of their installation – whereas the last example does go some way towards addressing the problem of blockage through leaf fall. The moral here is make sure you do check if guttering anti blockage has been incorporated before completion, and if it has that the flow rate of the gutter has not been impeded.


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