Inverted roof
An inverted roof, also referred to as a ‘protected membrane’ or ‘upside down’ roof, is form of flat roof in which the waterproofing layer is beneath the thermal insulation rather than above it.
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.
For a case study of an inverted roof defect, see Inverted roof defect - case study.
[edit] Related articles on Designing Buildings
Featured articles and news
Net zero electricity grids BSRIA guide NZG 5/2024
Outlining the changes needed to transition to net zero.
CIOB Global Student Challenge 2024
Universitas Indonesia wins for second year running.
New project and cultural district described in detail.
The nature of EPCs, crticism and inaccuracies.
History, issues and redesign.
From waste recycling to energy performance the hierchy.
An introduction to WERCS and WEEE responsibilities
Dealing with 2 million tonnes of waste equipment a year.
Global BACS Market: analytics and optimisation
A BSRIA glance at building automation and control systems.
What it is and how to use it.
Types of insulating plaster by binder and insulant.
Investors in People: CIOB achieves gold
Reflecting a commitment to employees and members.
Scratching beneath the surface; a guide to selection.
ECA 2024 Apprentice of the Year Award
Entries open for submission until May 31.
UK gov apprenticeship funding from April 2024
Brief summary the policy paper updated in March.
For the World Autism Awareness Month of April.