Meir Roofing

Extruded polystyrene boards have similar thermal movement and heat sensitivity characteristics to expanded polystyrene but have an improved thermal conductivity, low water absorption, high compressive strength, is flame-retardant, reduces thermal stress and saves heating and cooling energy. When selecting a thickness to achieve a specific U-value for an inverted roof, it is necessary to allow for the loss in efficiency due to the cooling effect caused by water draining through the insulation. The normal method to take this into account is to add 20% to the thickness of the board. The cooling effect can be reduced by the use of a suitable waterproofing membrane laid on the top of the insulation.   It is suitable for a number of applications including walls, floors, car park, high compressive strength applications and because of its exceptionally resistant to water absorption is suitable in an inverted roof system. Application in the protected membrane roof system consists of laying the boards loose above the waterproofing with anchorage against wind uplift and protection from ultra-violet degradation provided by a loading coat of gravel with a minimum size in the order of 20mm or paving slabs. A suitable loose laid geo-textile underlay may also be applied to even out surface irregularities or, if the waterproofing has a rough or sharp surface, to prevent abrasion to the underside of the board. Fine granules can work their way through the joints of the insulation and can cause damage and instability if they accumulate on the underside of the insulation. If it is expected that significant quantities of fine gravel will be present, it will be necessary to add a filter layer on top of the in addition to the waterproofing membrane insulation to act as a sieve and prevent the passage of fine material through the joints blowing under them
Interlocking extruded polystyrene panels are available with a decorative cementitious surfacing, to provide an inverted roof which is light weight, but will not need additional loading. The interlock ensures safety against wind forces within limits prescribed by the manufacturers. A special grade of panel is available with a reinforced decorative cementitious surfacing for pedestrian terrace decks. This surface is suitable for foot traffic only or light maintenance traffic. It is desirable to provide an even substrate which is free of undulations and which provides a continuous support for the panels. This will reduce the risk of panel breakage under foot traffic. The roof system must be impermeable and secure against wind. Panels must be protected from wind, edges against parapets and abutments should have panels set back about 50mm and the space filled with clean gravel. Panel joints are set open by 1mm to allow for thermal movement. The roof waterproofing should be installed to falls to prevent significant ponding, which could give rise to the flotation of the panels which may result in the need to install additional loading to prevent floatation. In all cases the detail of design and application must be in accordance with the manufacturer’s instructions