Roof Drainage Solutions to Stop Ponding on Flat Roofs

Why is Roof Drainage Important?

As part of Building Regulation Part H it is a requirement 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.

What does standing water do to a roof?

• It increases the load on the roof structure which can cause the deck to deflect, making further drainage harder.
• It can lead to the build of debris on roofs which in turn can lead to the blocking of outlets and the roof becoming unsightly.
• In winter ice could become a slip hazard.
• In the event of the roof being damaged the interior could suffer from greater water ingress.
• Reduces the lifespan of the roof materials
• increases plant life leading to further roof problems (blocked outlets, damaged roof materials)

Common causes of ponding water on a flat roof:

• Poor roof design with no (or an inadequate) slope
• roof deck subsidence
• Inadequate number of drains
• blocked roof drains

Roof Drainage Options:

• Internal drains
• Gutters and downspouts
• Parapet or Balcony Outlets (through wall outlet)