Elastomeric, TPO or EPDM

Start with the shape of the roof

Two of the three are single-ply membranes, TPO and EPDM: one thin, wide sheet does all the waterproofing. The elastomeric membrane stacks two plies of modified bitumen, in narrow strips.

The roof of a duplex or a triplex is nothing like a warehouse roof. It is small and cluttered: parapets, a chimney, vents, a skylight, sometimes a rooftop terrace. On such a roof, the large sheet loses its advantage. The roofer has to cut it at each obstacle, and each cut becomes a detail that must not be botched. Narrow strips suit a cluttered roof better.

On a garage, an addition or a building with no obstacles, the reasoning flips: a single-ply membrane installed with care gives a very good result there.

EPDM, rubber in large sheets

EPDM is a synthetic rubber, delivered in very wide sheets and often black.

• What it does well: it stays flexible in deep cold, it is light, and a simple roof can be covered with few seams.
• What it does less well: its seams are not fused, they are glued or joined with tape. Over the years, those seams need watching.
• Order of magnitude: 20 to 30 years, depending on the manufacturers and the quality of the installation.

TPO, a plastic welded without a flame

TPO is a flexible plastic sheet, often white. Its seams are welded with hot air.

• What it does well: its smooth white surface reflects a lot of sunlight, its wide sheets reduce the number of seams, it is light and installing it needs no open flame.
• What it does less well: the sheet is thin. A sharp object or debris damages it more easily.
• Order of magnitude: 20 to 30 years, depending on the manufacturers and the quality of the installation.

Elastomeric, thick and granulated

Elastomeric rolls are thick and covered with granules.

• What it does well: it takes foot traffic and resists punctures, it can be cut around obstacles, it can be repaired with a patch, and local roofers know it well.
• What it does less well: it has many more seams, takes longer to install, weighs more and often calls for a torch.
• Order of magnitude: 25 to 35 years, depending on the manufacturers and the quality of the installation.

What Laval's Code adds to the choice

Section 379 of the Code de l'urbanisme (Laval's urban planning code) names all three membranes in its list of permitted roofing materials.

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. The 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.

TPO is sold in white. For elastomeric, everything depends on the granules of the finish ply. For EPDM, look closely at the version offered. Ask us for the manufacturer's data sheet and submit the project to the City's Service de l'urbanisme (urban planning department) before signing.

Frequently asked questions