Elastomeric membrane

Bitumen given some flexibility

Left as is, bitumen hardens and cracks in the cold, and softens in the heat. Manufacturers blend in a polymer that behaves like rubber. The mix bends in January without splitting and holds its shape in July. Modified bitumen and elastomeric refer to the same product.

Inside each sheet is a reinforcement, of polyester or fibreglass. This reinforcement keeps the sheet from tearing when it is pulled.

On a flat roof in Laval as elsewhere, the system has two plies. The first, smooth, stops the water. The second, on top, is covered with ceramic granules. These granules shield the bitumen from the sun and give the roof its colour. Torched or glued depending on the product, the two plies end up acting as one.

What it handles poorly

• Careless installation. A poorly melted or poorly glued seam looks the same as a good seam on the day of the work. The defect shows up years later.
• Fire. The traditional method uses a torch, very close to wood that may be old and dry. It takes a trained crew and strict precautions.
• Water that does not drain. A puddle that lasts a day does it no harm. A pond that settles in for good wears away the granules and tires the seams.

Why roofers often suggest it

The climate does not scare it. Between winter frost and summer heat waves, a roof here goes through many freeze-thaw cycles. Modified bitumen moves with them instead of cracking.

It doubles the protection. The seams on top do not line up with those underneath. If one ply has a weak spot, the other slows the water down.

It fits cluttered roofs. Parapets, vents, chimney, skylights, party wall: the rolls can be cut and fitted to each obstacle.

It can be patched. For a tear or a gaping seam, a torched patch is enough, and the rest of the roof is left alone.

The trade knows it well. Many roofers install it routinely. That makes the roof easier to maintain twenty years from now.

Granule colour and Laval's rule

The top ply is sold in several granule colours, including white.

In Laval, section 379 of the Code de l'urbanisme (Laval's urban planning code) lists elastomeric membrane among the permitted roofing materials, without mentioning colour. On a flat roof, section 380 also applies. It requires a green roof, a white material, painted white or covered with a reflective coating or white ballast, a material with a solar reflectance index of at least 78, or a combination of these coverings. This index must be attested by the manufacturer's specifications or by a professional's specification. The Code does not say what applies to an existing roof redone identically.

Two pale granules do not necessarily have the same index. Ask us for the product data sheet, and have your project confirmed by the City's Service de l'urbanisme (urban planning department).

Frequently asked questions