The thermal insulation of flat roofs is a particularly important issue both in winter chills and summer heat. The performance and longevity of flat roofs depends upon many factors, including the position of the insulation within the construction. Due to its numerous advantages for flat roofing one of the best solution is the inverted roof construction.
• protected waterproofing-membrane,
• the roofing membrane is installed on the roofdeck (concrete deck),
• simple build-up without additional vapour barrier,
• the installation of the layers above the membrane is independent from weather,
• easy and fast installation,
• simple exploration and leak repair
The closed cell structure design of RAVATHERM™ XPS thermal insulation is perfect for inverted flat roofs.
• inverted roof with gravel
• green roof
• terrace roof
• parking roof
• duo roof
The advantages of the inverted roof reveal themselves when compared to any other flat roof solution. Because of the danger of condensation, the complex structural design, and the problematic breathability, the double shell cold roof, as a possible structural design solution for flat roofs, is not commonly used. Even though it provides a perfect solution, the straight layer order type of the single shell warm roof has a shorter life expectancy due to the water insulation’s exposure to weather and its implementation without mechanical protection in general, and in the case of failure it is also harder to find and repair the damage.
INVERTED ROOF ADVANTEGES
The inverted flat roof answers all physical, implementation, and operational/usage problems by placing the thermal insulation above the water insulation. The temperature of the thermally insulated waterproofing membrane is roughly the same during the whole year, and in addition to the appropriate mechanical protection, RAVATHERM™ XPS also provides protection against UV radiation. The upside down roof structure is the safest solution for waterproofing and for the operational spaces located under the roof.
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 dew point 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.
THE LONG LASTING FLAT ROOF
The inverted roof insulation system has been proven successful for more than four decades in Europe. The longterm behavior of the system has been examined by independent institutes and building experts several times.
Their assessments can be summarized as follow:
The life expectancy of the membrane is higher, the risk of failure is reduced, due to the effective and permanent protection for the membrane.
Significant reduction of thermal performance at correct installation and applying diffusion-open coverings are not to be expected.
INSTALLATION OF THERMAL INSULATION IN INVERTED ROOFS
In order to design an appropriate inverted roof and use it in the long-term, respect the following advice:
- The slope and design of the screed under the waterproofing membrane should comply with the professional guidelines. The use of waterproofing, e.g. bituminous plate, glued on the entire surface is recommended. In the case of utilised roofs, the use of PVC waterproofing membranes is to be avoided.
- The thermal insulation boards should be laid loosely, in an offset bond on the roof. The boards can be cut to size using a hot-wire cutter or thick-toothed saw on site.
- The filtering, separating and surface-stabilizing layer, that is, the geotextile or water-guide film should be a non-absorbent material to avoid the possible creation of a water film over the thermal insulation boards.
The thickness of the ballast layer should be dimensioned for wind-suction, but it should be a 50-mm thick washed 16/32 gravel layer. Adjacent to attic walls and roof superstructures, concrete tiles may be used as additional load based on the calculation.