Flat roofing

EPDM systems are often referred to as rubber roofs or membrane roofs. Other rubber and rubber-like materials used are chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CSPE, trade-named Hypalon), and polychloroprene (Neoprene).

EPDM is a thermosetting elastomeric polymer that must be bonded using appropriate adhesives. The material is made from:

• clay, which gives fire resistance;
• carbon black to increase tear strength and resistance to ultra violet light;
• process oils for flexibility; and
• curing agents for vulcanisation.

Usually membranes are laminated together out of 2 plies. Like all single-ply membranes, workmanship and proper detailing are essential for proper performance.

EPDM roofs are not maintenance free and need to be inspected regularly to identify the early signs of system or detail failure. Manufacturers claim a life expectancy of at least 25 years for EPDM and despite early failures this does not appear to be optimistic.

Roof systems can be either fully bonded, mechanically fixed or loose laid and ballasted, the latter being unsatisfactory in conditions of high exposure because of the risk of wind scour. Performance data on EPDM roofing is not always easy to come by. Manufacturers are, for commercial reasons, disinclined to publish information on membrane failures or system faults. Continual product development does mean that troublesome details and methods are gradually improved and so it is not necessarily appropriate to judge performance on historic usage.

A 1990 study of EPDM membranes of between 6 and 13 years old revealed that a high proportion of roofs exhibited defects of one form or another. Of the sample roofs, 87% had had one warranty claim, while 67% had had multiple claims. (Wallace, T.J. and Rossiter, W.J., ASTM Committee D-8 on Roofing, Waterproofing and Bituminous Materials, ASTM International, 1990)

Many of the defects identified reflected workmanship and maintenance problems rather than inherent faults with the systems themselves. Judgment of the system based on old data would be unfair, since during the intervening period a number of advances have been made, such as improvements in bonding, elimination of neoprene flashings and their substitution with EPDM flashings, improvements to edge detailing and so on.

Typical defects with EPDM roof coverings, derived from ASTM Committee D-8 report, are summarised:

• Puncture damage: Most often caused by a failure to drive home the mechanical fixings to insulation boards fully, leaving the fixing pin slightly proud of the stress plate. The pin can then gradually work its way through the membrane under normal loading or foot traffic.
• Embrittlement of flashings (depends on age of installation): Often neoprene based detail flashings at wall abutments or other perforations, exhibiting signs of checking, splitting and cracking where exposed to south and west and where overworked during installation - forming by hand or with roller tending to thin the material.
• Contamination: Contamination of flashings or field membranes with bitumen derived from previous roof coverings. Also contamination by grease or oil from roof mounted plant, extract equipment, etc. EPDM-based membranes are sensitive to hydrocarbons and should not be used in areas that are likely to become contaminated.
• Delamination: Interphasal delamination of insulation facing sheets when bonded to fully adhered EPDM membranes. Possibly due to manufacturing faults with the insulation (see rigid foam insulation). If this occurs, the roof membrane may be at risk from wind uplift.
• Seam defects: Birdsmouthing of seams, particularly at 3-way junctions due to poor workmanship, adhesion failure, contamination of contact surfaces, etc. Moisture working its way into seams can disrupt the integrity of neoprene-based splicing cement resulting in the gradual debonding of the entire seam. Since the 1980s, EPDM sheets have commonly employed factory applied adhesive seams rather than having to rely on site-applied adhesive.
• Wrinkles in the membrane: Possibly due to inadequate attachment, curling of insulation or contraction of the membrane after installation.
• Poor dimensional stability of insulation: Places undue levels of stress on the membrane.
• Defects in finishes: Risk of puncture from sharp debris left in ballast, or wind uplift due to missing paving slabs, wind scour of ballast, etc.
• Defects in membranes: Due to poor or misguided attempts at repair using inappropriate or incompatible materials.