Single-Ply Roofing Attachment Methods Explained
You’re reroofing with a single-ply membrane. Choosing between polyvinyl chloride (PVC), thermoplastic polyolefin (TPO), or rubber (ethylene propylene diene monomer, aka EPDM) isn’t the only decision you’ll need to make when planning your project; how it’s installed is equally important.
The three most common attachment methods are fully adhered, mechanically attached, and ballasted. Let’s explore each and the factors that may influence your decision.
Fully Adhered Single-Ply Membrane
“A single-ply membrane is fully adhered when it’s glued to the substrate using water-based contact adhesives, moisture-cure urethane adhesives, or solvent-based adhesives,” explains Jack Kenney, Vice President National Account Manager, D. C. Taylor Co., Cedar Rapids, IA. This is achieved by folding back the length of the membrane and coating both the underside of the membrane and the insulation or coverboard. The membrane is then folded back flat and smoothed out. Seams are hot-air welded.
This application method may result in a longer warranty, but odors can be strong; consider closing air intakes so building occupants are not affected. Additionally, the temperature must be above 40 degrees for adhesives to bond properly. On the upside though, it’s usually easy to locate a leak on a fully adhered roof.
Mechanically Attached Single-Ply
“Mechanically attached is the most common attachment method,” says Kenney. Unlike fully adhered applications, mechanically attached roofs can be installed when temperatures are cooler because adhesives are not used. “The membrane is attached using a mechanical anchor set through a seam plate or batten bar,” he adds. The substrate (e.g. wood, concrete, or steel) determines the type of fastener used, and code requirements specify the spacing of fasteners.
This is a faster means of installation. “Not having to install adhesives or purchase adhesive also causes the mechanically attached designs to be lower cost systems,” Kenney relays. The downside to mechanically attached membranes, however, is that air under the membrane may cause it to lift and flutter.
Ballasted Single-Ply Roof
Ballasted roof membranes are not adhered to the roof substrate but rather loose-laid and weighted down with washed river gravel, pavers, or an inverted roof membrane assembly (IRMA). These materials both keep the waterproofing membrane in place, as well as protect it from UV damage, foot traffic, and inclement weather. Finding a leak can be a challenge on a ballasted roof though, and it’s important to make sure the roof can support the added weight of the ballast. “Ballasted membrane attachments have fallen off in usage,” notes Kenney.
Your roofing contractor will collect information from you, your municipality, and your insurance provider to make a recommendation on the best roof system and attachment method for your project. Your budget, the type of roof deck, wind uplift and code requirements, structural load, building use, etc. will all be factored into the decision.