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Concrete Roof Decks - Embracing New Technology

Martyn Holloway, Business Development Manager Flat Roof for SFS intec, examines the options now available when fixing single ply membrane to concrete deck, in the wake of new technology.

16 March 2016

The fixing of single ply membrane to concrete deck has traditionally used an adhesive application approach but this is now being challenged by the advent of new technology. Martyn Holloway, Business Development Manager at SFS intec examines the options now available.

The application

Installing single ply membrane over a concrete deck is a common requirement for new build applications. This involves the application of a vapour control layer (VCL) followed by an insulation layer which is usually tapered. The single ply membrane layer is then installed. Refurbishment projects also require single ply membrane as an overlay to replace existing waterproofing systems.

The adhesive option

The deck must initially be primed and this is usually followed by a torch applied or self adhesive bituminous VCL. The insulation layer is subsequently adhered to the VCL and should this be made up of several layers, each must be bonded together. The single ply membrane is then adhered to the specialist insulation surface.

The mechanically fixed option

Polyethylene VCL is rolled out, joints taped and then overlaid by foil faced insulation boards which are mechanically fastened to the concrete deck. Should multiple layers of insulation be used then fasters are applied  through the top board. The single ply membrane is mechanically fastened through the membrane laps or in the case of field fix systems welded to proprietary insulation plates.

Advantages & benefits of each

The adhered application method requires no drilling into the concrete substrate. Adhesive applications however can be weather dependent and the design is limited by a specified maximum wind load exposure. The application of the correct adhesive weight for each layer will be down to the judgement of the installer on site. In comparison, mechanically fastened applications are less weather dependent. Mechanical fastened schemes can additionally be used in all exposure zones providing predictable and reliable performance. Tensile performance can be measured by pullout testing and the appropriate design load per fastener calculated to provide the correct fixing pattern which can be inspected after installation. In the case of refurbishment applications, existing bonded layers can be secured with mechanical fasteners to ensure that the complete roof build up will last for the lifetime of the new waterproofing membrane.

Mechanical fastening innovation

The days of drilling deep holes and hitting reinforced bar to accommodate tapered insulation boards are long gone! Adjustable insulation fastener systems such as the SFS intec TIA system are specifically designed to self-adjust to the insulation thickness, as the fastener engages the sleeve as well as the concrete deck. The TIA system requires 5mm diameter by minimum 25mm deep pilot holes for all settings, compared with conventional practice of 60mm or deeper pilot holes for tapered schemes.

Induction welding offers significant benefits to the contractor. The SFS intec isoweld® system uses heat induction to weld the membrane to a specially coated metal stress plate located underneath the membrane which is mechanically fastened to the deck. The heat induction welding method provides an extremely secure fix, without penetrating the waterproof membrane. This field fix system enables the installer to use the widest membranes available and thereby significantly reduce the amount of seam welding required. Additionally because fixing is not in-seam, less overlap is required offering increased membrane coverage. Up to 40% fewer fasteners (and 40% fewer pilot holes) are required. The isoweld® plates can be installed with the TIA fixing system for tapered schemes thereby offering additional labour and cost savings.

Furthermore, induction welding offers a fast, easy and cost effective solution for fixing membranes to concrete parapet walls.

Cost savings

So how do the costs compare? Not surprisingly mechanically fixing offers a significant cost saving opportunity to the contractor. Sizeable material and labour cost savings can be made by not priming the deck, using a polyethylene VCL instead of bitumen, removing the adhesive bonding of individual layers and using thinner foil faced insulation. Combine the cost savings of a mechanical fix with an induction welding application, that offers typically 40% fewer fasteners, increased membrane coverage and an adjustable fixing system for tapered insulation (requiring less drilling) and additional savings are possible.

Conclusion

With the advent of new technology, contractors should challenge traditional approaches to work practice. The application of single ply membrane to concrete decks is no exception. New mechanical fixing options offer the roofing contractor improved security and peace of mind combined with real cost saving opportunities.