Flat roofs and falls

Flat roofs and falls

Flat roofs are not designed to be 100% flat. Well, they shouldn’t be anyway. Instead, flat roofs need to be designed on a very slight gradient, to transport water away from the roof, as quickly as possible. A gradual slope is the best way to achieve this, as rainwater naturally follows gravity. But how are falls created for flat roofs? And why should you create falls for flat roofs? Well, here at Enviroply Roofing, we are leading commercial and industrial roofing experts, providing high quality, professional roofing services across the North West. As a result, we have produced this guide to all you need to know about flat roofs and falls.


Flat roofs and falls

Flat roofs might look flat, but actually they should have a slight gradient. This can be created through a couple of different options, including:

  • Tapered insulation- This is a lightweight, effective, and convenient way to create a fall for a flat roof, especially on a concrete deck which is installed level, when using a single ply roofing membrane. The insulation and vapour barrier is laid on top of the roof deck, providing thermal insulation for the property below, but also changing the gradient to create an artificial fall. The single ply roofing membrane is then applied on top of the insulation.
  • Sloping decks- by altering the roof deck itself, and laying the supporting beams or joists at a slope, you can create a sloping deck.
  • Firrings- Firrings are tapered shaped timbers that are fixed along the tops of the joists before the deck is laid. These firings should be the same width and length of the joists. The firrings may also provide the fall by each one decreasing in thickness along the slope of the roof.


Advantages of creating falls for flat roofs

So why should your flat roof have a slope, instead of being perfectly flat? Well, there are a number of advantages to a flat roof with a slightly sloping gradient. These advantages include:

  • Effective drainage- on a flat roof with a slight slope, rainwater will be directed easily into the gutters and drains and carried away from the roof.
  • Prevent ponding- ponding is a common problem for flat roofs with improper drainage. Ponding occurs when rainwater gathers in pools on the flat roof, as it is unable to drain off. This causes a range of problems, including:
    • creating a build up of dirt and leaves that can obstruct gutters and drains and become a slip hazard
    • challenge the structural integrity of the roof itself as it supports the increased weight of the water
    • Roofs with extensive ponding require increased maintenance input.
  • Adhere to standards- a key requirement of Building Regulation Part H is that that adequate provision be made for rainwater to be carried away from the roof of the building. For your commercial or industrial property to be up to standard, creating a sloping roof is necessary.

For more information or for professional roof design and installation, get in touch with the professionals today, here at Enviroply Roofing.