Pitched roofs

7.2

7.2.22Drainage

Roof drainage shall adequately carry rainwater to a suitable outlet.

Drainage should be:

  • provided where roofs are greater than 6m²; however, consideration should be given to providing drainage to smaller roofs such as dormer, porch roofs and balconies (see Clause 7.1.12)
  • of a sufficient size to accommodate normal rainfall, and sized to cope with concentrated flows, i.e. where there are dormer roofs
  • designed and fitted to prevent erosion of the lower surface, where water from a large roof surface discharges onto another surface
  • fixed in accordance with the design, using the correct type of fittings for internal and external angles, outlets etc. to ensure efficient drainage of the roof
  • supported and jointed in accordance with the manufacturer’s recommendations
  • insulated when passing through a home, in accordance with Chapter 8.1 ‘Internal services’
  • installed ensuring gutters are provided with stop ends, and are laid with a sufficient fall towards the outlet, unless designed to be flat.

Where gutters are behind parapet walls, a suitably sized overflow should be provided.

Where a downpipe discharges above ground level, or above a drainage gully, the downpipe should be fitted with shoes.