Fully Adhered Roof System

In a fully adhered roof system, the membrane is bonded continuously to the insulation, cover board or deck beneath it. Bonding may use contact adhesive applied to both surfaces, water-based or low-VOC adhesive, low-rise polyurethane foam adhesive, hot asphalt, torching, or a factory-applied self-adhesive backing.

Membranes

• EPDM: bonded with contact adhesive or as fleece-backed sheet set in adhesive.
• TPO and PVC: smooth or fleece-backed sheets in contact or foam adhesive.
• PIB: usually fleece-backed and bonded with cold adhesive.
• Modified bitumen and BUR: inherently adhered by mopping, torching or cold adhesive.
• Liquid-applied membranes and spray foam: bonded by their nature.

Advantages

• smooth, wrinkle-free appearance
• no billowing, because wind cannot get under the sheet
• uplift resistance governed by the bond and substrate attachment
• easier leak tracing, since water cannot travel far under a bonded sheet
• suits complex roofs, curved surfaces and areas where fasteners are undesirable

Limitations

Full adhesion is slower than mechanical fastening, uses large quantities of adhesive, and is sensitive to temperature, humidity and substrate moisture. Solvent-based adhesives release VOCs and odour; water-based products need warm, dry curing conditions. The substrate must be clean, dry and strong enough; facer delamination of insulation or a weak cover board can become the failure point in high winds, which is one reason cover boards are common under adhered membranes.

Fleece-backed sheets

Fleece-backed membranes, made in EPDM, TPO, PVC and PIB, carry a non-woven fabric on the underside. The fleece provides a bonding surface for adhesives, protects the membrane from rough substrates, and makes these sheets popular for recovering old roofs.