- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 13 Nov 2017
The waterproofing layer is typically a liquid-applied membrane above a concrete roof slab, with insulation boards laid over the top, weighted down with either paving slabs or gravel ballast to protect against wind uplift and flotation. Rainwater percolates down through and between the insulation boards to the membrane where it is drained away through rainwater outlets.
One of the main benefits of the inverted roof method is that the membrane is protected by the insulation from the expansion and contraction caused by weather fluctuations, such as frost and solar radiation. It is also protected from damage by traffic on the roof, such as people walking, the movement of equipment and so on.
When calculating the U-value of the roof, consideration must be given to the fact that the insulation is likely to be wet a lot of the time, with some moisture trapped beneath the boards. This can create the risk of condensation occurring within the build-up of the roof, as the temperature of the membrane can be below the dew point. However, once the roof deck (and the membrane) warms up, the condensation will be able to evaporate. Problems can occur if the accumulation of condensation persists.
For more information, see Specifying insulation for inverted roofs.
 Related articles on Designing Buildings Wiki
Featured articles and news
Matt Rhodes, Quiss Technology, explains how an increasing number are falling victim to sophisticated cyber-attacks.
Assembly drawings represent items that consist of more than one component and show how they fit together.
Is the water sector under too much pressure from the regulator?
Everything you need to know about acoustics in under 800 words.
Check out our list of the 90 most unusual buildings of all time.
The government is to set a personal consumption target to reduce water use.
BSRIA calls for more education to promote fuels that are fit to burn.
Michael Gove admits air pollution is making people ill and shortening lives.
BRE call for a clearer, focused drive for the delivery of sustainable, quality developments.
Proposals for a 140m high observation wheel next to the Tyne.
Consistently one of our most popular articles - so just how much do you know about BoQ's?