Inverted Flat Roofs

In an inverted roof construction the Sarnafil membrane is installed directly to the structural decking (usually concrete) and the SarnaTherm XPS (extruded polystyrene) thermal insulation is laid exposed on top of the waterproofing membrane's protection layer. Then SarnaTherm Aquazone® a high performance non-woven polyethylene WFRL (Water Flow Reducing Layer) is installed over the insulation to minimise the 'cooling effect'  associated with rainwater flowing down through the insulation and away, reducing the insulation's thermal performance in the process. It is critical the WFRL layer is installed correctly, as this significantly reduces the insulation thickness required for a given U-Value. An air and vapour control layer is not required.  

This type of roof is generally used where there is going to be a requirement for paving (or another surface finish) for use as a roof terrace or balcony area. A minimum ballast weight of 80kgs/m² is normally required in order to resist wid uplift forces and adequately secure the loose laid inverted roof system. The ballast requirement may increase in some locations, depending on the specific type of building, exposure/location and surface finish.  

Sarnafil carry out thermal and condensation risk analysis for every project inclusive of SarnaTherm insulation. Furthermore a bespoke designed system eliminates any performance and design issues