Roofing Give-and-take

Andy Fell of Hambleside Danelaw summarises the pros and cons of different flat and low-pitched roofing membranes


ousing maintenance is a demanding task, with cost, performance, lifespan, ease of installation and maintenance being the main governing factors. ‘Traditional’ roofing systems are still considered to

be valid for certain applications, but there are alternative products that should always be appraised for their merits.

BITUMINOUS A good, robust product compatible with many other systems, with extremely good flexibility and resistance to rupture. Naked flame use however makes this a risky choice on combustible substrates, and the heavy environmental cost of sourcing and manufacture weigh against it.

PVC Aesthetically pleasing, speedy to apply, easy to make a roof look decorative using standing seams applied to the surface. But, as well as being difficult to repair after long-term weathering, the potential for damage by following trades makes the specification of PVC waterproofing one to give serious consideration to if a roof is going to be trafficked.

TPO Fairly robust, aesthetically pleasing, speedy to apply, and easy to make a roof look decorative using standing seams applied to the surface. TPO however is incompatible with many other membranes, especially bitumen, and can be difficult to repair after weathering. Like PVC, the potential for damage by following trades makes the specification of TPO waterproofing one which requires careful consideration.

The suitability of alternative waterproofing systems for refurbishment work does offer a wide choice

LIQUIDS Polyurethane and PMMA (Poly Methyl Methacrylate) liquid systems can be ideal for awkward detailing with multiple roof penetrations. Quick curing acrylics such as PMMA are ideal for trafficked surfaces, but for refurbishment, these systems rely more heavily on the quality of preparation and condition of the underlying layers and substrate to be successful, so the relatively high cost of the product, added to extensive preparation can lead to an expensive system; the cost of which exceeds many other solutions.

EPDM This can be a very hard wearing and robust waterproofing material which is usually adhered to the roof or laid loose and ballasted. However, failed EPDM roofs generally happen because detailing is more difficult to achieve, and the adhesive bonding upstand membrane can disengage from the substrate, causing flashings to fall away. Additional fixing at edge detailing is generally required, which usually means fixing through the completed membrane. | HMM March 2018 | 45

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