EPDM membrane: rubber in large sheets

Fewer seams, more give

A single sheet of EPDM can cover a wide strip of roof. Fewer seams means fewer places where water can get through.

The rubber stretches and contracts with the building, from heat wave to frost, without cracking. Of all commercial roofing membranes, it is one of those that best withstand temperature swings.

EPDM suits large, simple roofs with little equipment, such as those of a warehouse, a plant or an institutional building. Its lifespan is in the range of 20 to 30 years, according to manufacturers and depending on the quality of installation.

Glued, screwed or ballasted

• Glued. The whole sheet is adhered to a cover board.
• Screwed. Bars or plates fasten it to the deck.
• Ballasted. The sheet is simply rolled out, then weighed down with round stone or pavers that hold it in place.

Ballast goes down quickly and shields the rubber from the sun. It is heavy, however. On an existing building, a structural engineer must first confirm that the roof can carry it.

Another drawback: to look for a leak, we have to move the stone. Under a sheet that is not glued, water can travel far before it shows inside.

Seams first

EPDM does not melt with heat like a thermoplastic. The sheets are joined with a primer and an adhesive tape made for this material. If the surface was dirty, damp or poorly primed, the seam eventually opens.

Faced with a leaking EPDM roof, we look, in order, at:

1. the seams from one sheet to the next,
2. the upturns at the parapets, where the membrane can shrink and pull on its fasteners,
3. the flashings around drains, vents and equipment.

What to know before choosing it

• It does not like grease. Petroleum products and cooking grease degrade the rubber. Near a restaurant hood, protection is needed.
• It does not tolerate bitumen. Tar and bituminous sealants are incompatible with it. A makeshift repair done with the wrong product makes things worse.
• It is often black. Black absorbs heat. White versions exist.

A black membrane on a flat roof in Laval

Section 379 of the Code de l'urbanisme (Laval's urban planning code) names EPDM membrane among the permitted roof coverings. It names it in a passage that also mentions materials certified as white roofing, and it says nothing about a black membrane. The City's Service de l'urbanisme (urban planning department) has to answer that. On a flat roof, section 380 also requires a green roof, a white material (or one covered with a reflective coating or white ballast) or a solar reflectance index of at least 78. A black membrane raises the question of the index. The manufacturer, or the professional who signs the specifications, has to attest it. The Code does not say what applies to an existing roof redone identically. The City has to answer that, through the Service de l'urbanisme, before you order.

Frequently asked questions