Inverted Roofs
The performance and longevity of flat roofs depends upon many factors, including the position of the insulation within the construction.
If insulation is placed below the structural deck (cold roof construction) the structure remains cold and there is a considerable risk of condensation; for that reason cold deck roofs are not recommended and are now seldom used.
Insulation placed above the structural deck and beneath the waterproof layer (warm roof construction) reduces the risk of condensation but, because the waterproof layer is thermally isolated from the rest of the roof construction, it is exposed to wide temperature fluctuations with consequent increased risk of premature failure (Figure 01).
The inverted roof concept overcomes the problem by placing thermal insulation above the waterproof layer, maintaining it at an even temperature close to that of the building interior and protecting it from the damaging effects of UV radiation and from mechanical damage.
The insulation protects the waterproof covering from:
- wide temperature variations - +80 to –20°C.
- degradation from weathering.
- mechanical damage during construction, use and maintenance.
The waterproof layer acts as a total vapour control layer and, being on the warm side of the insulation, is maintained above dewpoint temperature so the risk of condensation is eliminated.
The inverted roof concept has other benefits. The insulation can be:
- installed in any weather.
- added to, without stripping the waterproof layer.
- easily lifted and replaced/re-used if the building is altered.
