Rob Edwards, Specification Sales Director at SIG Design & Technology, discusses the benefits and practicalities of using EPDM on large-scale flat roofing projects with Architecture Today’s Technical Editor John Ramshaw

EPDM flat roofing has risen to prominence in recent years for many reasons – not least its cost-effectiveness, life-expectancy, durability and fire performance. However, the material is often up against stiff competition in the form of PVC, liquid products, bitumen and other single ply membranes when it comes to specifying large-scale commercial roofs. So how does EPDM compare to its rivals? How should architects approach the design and specification processes? And are there any downsides to the material’s use? Rob Edwards, Specification Sales Director at SIG Design & Technology, discusses these questions with Architecture Today’s Technical Editor John Ramshaw.

What is EPDM roofing?
EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber roofing membrane originally pioneered by Carlisle SynTec in the USA. The company first used the material on the rotunda at Chicago’s O’Hare International Airport in 1961, and nearly 60 years later it is still protecting the building. Continuous innovation and refinement has led to today’s high-performance products, such as SIG Design & Technology’s Sure-Seal EPDM Roofing systems. Backed with a 20-year warranty, the BBA-approved membranes are said to be ideal for commercial flat roof installations, and feature industry-leading UV resistance and excellent weather resistance. Among the most recent product developments is Carlisle SynTec’s RapidLock Roofing System, which favours Velcro over traditional adhesives to meet and exceed wind uplift requirements. The versatility and labour-saving aspects of the system means that is already gaining traction in the US and is likely to become available in the UK.

EPDM re-roofing of Lotus Court, a block of three residential units in Stafford (ph: Crescent Roofing)

Why choose EPDM for large-scale flat roofs?
One of the most important advantages of EPDM over other roofing types, such as PVC, single ply or bitumen, is speed of installation. Sure-Seal FleeceBack (reinforced) is available in sheets measuring up to 3.05-metres wide by 15.25-metres long. Using either a spray-applied polyurethane or acrylic deck adhesive, it is possible to install 45-square-metres of roof in approximately 20 minutes. Factory Applied Tape (FAT) seams reduce EPDM’s installation time further, with trials showing this to be around 75 per cent faster than non-FAT seaming methods. Combined with a 3.05-metre wide roll that already has 67 per cent fewer seams than bitumen felt, a completed roof section requiring no further work can be achievable in around 20 minutes. Standard Sure-Seal (non-reinforced) is available in far larger sheets – up to 15.25-metres wide by 30.5-metres long – and is perfect for ballasted systems.

EPDM roofs also provide a wide range of performance benefits. They can withstand extreme weather conditions, while remaining UV-stable and largely unaffected by ozone and heat. Fully adhered EPDM roofs are unlikely to tear, exhibit excellent puncture and impact resistance, as well as withstand normal roof traffic. Furthermore, EPDM roofs are able to accommodate structural movement, elongating as required over the lifetime of the building. It with withstands huge temperature fluctuations without suffering from thermal shock, and will not crack over time as many systems can. Last but not least, EPDM roofs, such as Sure-Seal and Sure-Seal FleeceBack, are brilliantly simple to install, requiring no specialist equipment.

EPDM re-roofing of teaching blocks at Hareclive E-ACT Academy in Bristol (ph: Crescent Roofing)

Are there any other benefits?
Unlike some single ply systems EPDM is plasticiser-free. This ensures that it remains flexible, pliable, and most importantly of all, adaptable throughout its lifetime. As such, building owners can retain the option to add skylights, sun tubes, or PV systems in the future. From another perspective, EPDM roofs remain repairable in the event of damage occurring. This may not be possible with roofing systems that become brittle or degrade with age, resulting in the need for a new roof.

Are there any disadvantages to using EPDM?
For some people, the slate grey colour of EPDM holds less visual appeal than other roofing materials. However, the material’s dark tone can be of benefit in the UK climate by converting harmful UV rays into heat, which can in turn help to maintain the condition of the substrate and internal temperatures.

Typical Sure-Seal EPDM box gutter detail (SIG Design and Technology)

How does the life-expectancy of EPDM compare to other roofing types?
EPDM can last for decades – as evidenced by O’Hare International Airport – resulting in fewer re-roofs and significant cost savings. Carlisle SynTec has subjected a range of flat roofing systems to Xenon Arc Weathering Testing. This exposes the membrane to a measured amount of energy and accurately reflects the effects of long-term weathering. PVC (1.5mm) failed at 12,600 kj/m², while Sure-Seal EPDM (1.5mm) reached 41,580 kj/m² without cracking or crazing. This suggests a potential membrane life-cycle of three times that of many PVCs. High-quality EPDM membranes, such as Sure-Seal and Sure-Seal Fleeceback, hold market-leading 35-year BBA Certificates.

How does EPDM rate in terms of cost?
Sure-Seal is comparable in terms of cost to many of the flat roofing systems it competes against. Sure-Seal Fleeceback comes at a premium, but the performance advantages and labour cost savings far outweigh the increased price point, resulting in excellent value for money.

Typical Sure-Seal EPDM parapet detail with 150mm Sureseal PS cover strip (SIG Design and Technology)

How should specifiers approach EPDM roofs in terms of detailing
EPDM detailing has progressed significantly over the years, with early seaming methods using splice cement giving way to pressure sensitive (PS) tapes that are faster, cleaner and more reliable. Detailing conditions that cannot be solved using PS tape are usually overcome with Sure-Seal pourable sealer, which works like a traditional pitch pocket. In general, specifiers should seek advice on detailing EPDM roofs from reputable manufacturers, such SIG Design & Technology, at the earliest opportunity. This will help provide workable solutions to unusual conditions and ensure the smooth running of projects when they get to site.

Is EPDM suitable for re-roofing projects?
Yes. Sure-Seal FleeceBack was originally designed with re-roofing in mind. A good example is overlaying an existing bitumen roof. If the original system is still largely performing, but approaching the end of its useful life, avoiding the risk of water ingress during the works and maintaining day-to-day activities within the building can be invaluable. Significant cost savings can also be made in terms of labour and material disposal, which can then be passed on to the building owner. In addition, the low odour and noise characteristics of EPDM systems, such as Sure-Seal, make them ideal for re-roofing occupied premises.

Typical Sure-Seal EPDM wall flashing detail (SIG Design and Technology)

How should specifiers approach the installation and maintenance of large-scale EPDM roofs?
In terms of installation, EPDM roofing should always be applied by a fully trained contractor. The SIG Design & Technology Accredited Contractor (DATAC) scheme provides assurance that SIG products are correctly installed. In common with other flat roof types, EPDM installations should be inspected at least annually, with any debris swept away and gutters (where used) cleared. While the material is naturally durable and damage resistant, cleaning it can further help to maintain its long-term strength and performance.

Contact Details
For more information on EPDM roofing please visit the SIG Design & Technology website.