What it is made of
Ordinary bitumen hardens in the cold and softens in the heat. Manufacturers blend in a rubber-like polymer to correct that. The result stays flexible in winter and holds its shape in summer. This blend is called modified bitumen, or elastomeric.
The bitumen coats a reinforcement, a polyester or fibreglass mat that gives the sheet its tear resistance. Everything arrives on site in rolls.
The system has two layers.
- The base sheet. It is smooth and forms the first barrier against water.
- The cap sheet. It is covered in ceramic granules that protect the bitumen from the sun and give the roof its colour.
The two layers are torched or glued, depending on the product. Once joined, they act as a single skin.
Why it dominates in Montreal
Among the systems installed on a flat roof in Montreal, elastomeric has taken first place.
It handles the climate. A Montreal roof goes from deep frost to heat waves, with dozens of freeze-thaw cycles in between. Modified bitumen follows these movements without cracking.
It offers two barriers. The seams of the cap sheet are offset from those of the base sheet. A weak spot in one layer does not immediately open a path for water.
It suits small, busy roofs. A triplex roof is full of details, with parapets, vents, a chimney, skylights and the neighbour's wall. The rolls can be cut and shaped around every obstacle.
It can be repaired. A tear or an open seam is fixed with a torched patch, without touching the rest of the roof.
Roofers know it. Most crews in the region install it every week. Finding someone to maintain it in twenty years will not be a problem.
Colours and reflective roofs
The cap sheet comes with granules in several shades, including white. Most boroughs require a reflective roofing when a flat roof is replaced.
Not all pale granules perform the same. Ask us for the data sheet of the proposed product and check with your borough that it meets the requirement.
Its limits
The elastomeric membrane has its limits.
- Installation is everything. A poorly torched or poorly glued seam does not show on installation day. It shows up years later.
- The flame. Traditional installation uses a torch, close to wood that is often old and dry. It calls for a trained crew and strict precautions.
- Standing water. The membrane tolerates a passing puddle, but water that sits permanently wears out the granules and seams faster.
Frequently asked questions
How long does an elastomeric membrane last?
An elastomeric membrane lasts roughly 25 to 35 years, depending on the manufacturer and the quality of installation. Drainage and maintenance weigh heavily on that figure. A neglected membrane on a roof where water sits will not reach the top of the range.
Can an elastomeric membrane be white?
Yes. The cap sheet is made with white or very pale granules. Reflectance requirements vary from one borough to another. Check that the chosen product meets yours.
Can a membrane go over the old roof?
Sometimes. A membrane can go over the old roof if the old roofing is dry and stable and the structure can carry the weight. If the insulation is wet or the deck is doubtful, the old roof must come off. Ask us to justify this choice in writing in the quote.
What is an elastomeric membrane?
An elastomeric membrane is a flat roofing made of bitumen modified with a rubber-like polymer, laid in two layers. The base sheet is the first barrier against water, and the cap sheet is covered in granules that protect the bitumen from the sun. The two layers are torched or glued, depending on the product.