Insulating Inverted Roofs
What is an inverted roof?
What are the main advantages of an inverted roof?
How long have inverted roofs been used?
Are there any long-term studies of the use of STYROFOAM™ in inverted roofs?
What finishes are suitable for an inverted roof?
Which products are used for the inverted roof?
Are there any special factors which have to be considered when determining the thickness of insulation required for an inverted roof?
Does an inverted roof have to have a separating layer?
Can an existing flat roof be converted to an inverted roof?
What is an inverted roof?
An inverted roof is a flat roof in which the thermal insulation is placed above the waterproofing membrane.
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What are the main advantages of an inverted roof?
First, the thermal insulation protects the waterproofing membrane from extremes of temperature, exposure to UV radiation and mechanical damage, greatly prolonging its service life. Secondly, the position of the insulation eliminates the risk of interstitial condensation within the roof. Consult Insulating inverted roofs for further information.
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How long have inverted roofs been used?
The inverted roof was developed by Dow in the 1950s and has proved its worth for more than 40 years throughout the world. To date, over 45 million square metres of ROOFMATE™ boards have been laid on inverted roofs in Europe.
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Are there any long-term studies of the use of STYROFOAM in inverted roofs?
Follow-up investigations of inverted roofs have shown STYROFOAM insulating boards do not lose any of their thermal or mechanical properties ten, twenty or even thirty years after installation.
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What finishes are suitable for an inverted roof?
Inverted roofs may be finished with aggregate, paving slabs, extensive or intensive planting, or parking deck systems.
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Which products are used for the inverted roof?
Primarily ROOFMATE SL-X, SL-A and LG-X. However, FLOORMATE™ 500-A and 700-A can be used where high loads e.g. air-conditioning units, Building Maintenance Units (BMUs) may be supported directly off the insulation. For ballasted and green inverted roofs specify FLOORMATE 500-A or 700-A.
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Are there any special factors which have to be considered when determining the thickness of insulation required for an inverted roof?
Allowance must be made for the cooling effect of rainwater which reaches the waterproofing layer. Normally a 20% increase in insulation thickness is required. However, with the ROOFMATE MinK system the rainwater cooling penalty is reduced to 2% (see Agrément certificate 97/3431). The final U-value required for the roof will depend upon the overall energy performance of the building (see Part L guide for further information).
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Does an inverted roof have to have a separating layer?
We recommend the use of separating layers in inverted roof constructions. Specify ROOFMATE MK, a water resistant, vapour open membrane. For further guidance see Separating layers.
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Can an existing flat roof be converted to an inverted roof?
Yes, in principle the thermal performance of a conventional flat roof can be enhanced by adding insulation above the waterproofing membrane. For more information see Renovation.
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