Flat roof

Flat roof 
Flat roofs are cheap to install, but may face issues with waterproofing.

What is a flat roof?

A flat roof is installed to sit horizontally on top of a building, with very little or no pitch. A flat roof is ideal in many ways - for example they're cheap, fast and easy to install. The key problem with flat roofs however, is they can be difficult to waterproof. A pitched roof encourages rain, ice and snow to drain or slide off. Water on a flat roof tends to pool and then soak down into the house.

If the issue of water drainage can be successfully dealt with, the top of a flat roof can be used as an extra living area without sacrificing any room inside the home. Without proper waterproofing though, water damage from leaks inside the home will outweigh the benefits of having the extra space.


What variations on flat roofs exist?


The key variations between flat roofs are in their pitch and function. Some flat roofs are more steeply pitched than others. A skillion roof describes a flat roof with a steep pitch. Low pitched flat roofs can be used for gardens or outdoor terraces. Another common use for flat roofs is solar panel installation.


What materials are typically used for flat roofs?

As flat roofs are particularly vulnerable to moisture penetration, they need to be properly sealed to ensure the building envelope remains tight and the inside of the building stays dry. Flat roofs were once typically covered with an asphalt and gravel mixture. This coating is not particularly durable though, as the asphalt tends to become brittle and then crack.

Aside from its poor long-term waterproofing properties, asphalt is not seen as a sustainable building product, and may release toxic chemicals into the atmosphere during production and installation. Recently, materials such as vinyl and rubber-based products such as Ethylene Propylene Diene Monomer (EPDM) have been chosen over asphalt for installation to create a roof membrane which helps to seal flat roofs.

A well sealed and maintained layer of rubber, combined with a pump or syphon system will help to keep interiors free from leaks. Solar panels, decking or even soil and grass can then be installed over the top of the vinyl or rubber membrane.


  • Easy to build
  • Cheap to build
  • Allows a good use of space
  • Prone to pooling and water damage
  • Lack of pitch increases load for bearing
  • Not suitable for areas prone to cyclones or strong winds