Creating drainage falls on a roof

It is a requirement of Building Regulations that adequate provision is made for rainwater to be carried from the roof of the building. It is generally considered good practice for flat roofs to be designed to clear surface water as rapidly as possible. According to BS6229 & BS8217, flat roofs should be designed with minimum falls of 1:40 to ensure a finished fall of 1:80 can be achieved, allowing for any inaccuracies in the construction. Water ponding on flat roofs should be avoided because:

  • It encourages the deposition of dirt and leaves which can be unsightly, may obstruct outlets and /or become a slip hazard.
  • In the event of damage, the interior may suffer greater water ingress.
  • It increases the dead load and may cause progressive deflection of the deck.
  • Ice may be a slip or wind hazard during the winter months.
  • Roofs with extensive ponding require increased maintenance input.
  • On an inverted roof this will create the situation where a thermal calculation is not possible.  Flotation of the insulation may also occur.

Tapered insulation systems are a lightweight, convenient and cost effective alternative method of providing falls to the roof and can be used with our reinforced bitumen membrane (RBM) and synthetic single ply roof systems.

Our Technical Department can design bespoke insulation schemes for individual projects and provide advice on roof fall design.

More about Bauder tapered insulation