The thermal insulation of flat roofs is an important issue both for winter chill and summer heat. The performance and longevity of flat roofs depend upon many factors including the position of the insulation within the structure. Inverted flat roof construction holds numerous advantages for flat roofing and provides the best solution because:
- the roofing membrane is installed directly on top of the structural deck
- the water-proofing membrane is protected by the insulation
- there is a simple build-up of layers without an additional vapour barrier
- the installation of layers above the waterproof membrane is independent of weather
- the insulation is easy and fast to install over the water proofing layer
- any defect in the waterproofing is simple to locate and repair, replacing the insulation afterwards
Inverted roofs comply with the building energy requirement that thermal protection should be unbroken and installed on the outside surface of the building structure. Thermal insulation efficiently reduces outbound heat flows when the building is heated, while in the summer it prevents building structures from warming up, thereby significantly reducing (or, ideally, excluding) the need for air conditioning.
The closed-cell structure design of XPS thermal insulation is perfect for inverted flat roofs, offering in addition use of the roof area as pedestrian terraces, for car-parking or green roof applications.
The advantages of inverted roofs are clear when compared to any other flat roof solution. Double-shell cold roofs are not commonly used for flat roofs due to the danger of condensation, the complex structural design and the problematic breathability. Single-shell warm roofs with a straight order of layers have a shorter life expectancy due to the exposure of the waterproofing layer to weather and if implemented without mechanical protection in general. It is also harder to find and repair the damage in the event of failure.
ADVANTAGES OF INVERTED ROOFS
The inverted flat roof answers all physical, installation, and operational/usage problems by placing thermal insulation above the waterproofing layer. The temperature of the thermally insulated waterproofing membrane remains roughly the same throughout the whole year, and used in conjunction with appropriate mechanical protection, Ravago's XPS insulation provides additional protection against UV radiation. The inverted roof structure is the safest solution for waterproofing and for the operational spaces located under the roof. The insulation protects the waterproofing layer from:
- wide temperature variations — daily 60 to 70°C and annually sometimes even exceeding 100°C (-20 to +80°C)
- degradation caused by extreme weather conditions
- mechanical damages 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 dew point temperature so the risk of condensation is eliminated.
The inverted roof concept has other benefits as well. The insulation can be:
- installed in any weather
- added to or replaced without stripping the waterproof layer
- easily lifted and replaced/re-used if the building is altered
THE LONG-LASTING FLAT ROOF
The inverted roof insulation system has been proven successful for more than four decades in Europe. The long-term behaviour of the system has been thoroughly examined by independent institutes and building experts.
Their assessments show that having an effective and permanent protection increases the life expectancy of the membrane and reduces the risk of failure.