Cladding options for a flat roof
A flat roof has special requirements, which is why there are different coating options to make it watertight.
On a flat roof, water can't drain off naturally as it does on a pitched roof, so it's carried away by a storm drain. To prevent it from being vulnerable to infiltration, flat roofs are covered with seamless cladding (i.e., no shingles), as water could seep into the interstices.
Asphalt and gravel surfacing
The oldest asphalt and gravel surfacing consists of four or five overlapping layers of felt soaked in liquid asphalt. The felt fills in structural imperfections and stabilizes the asphalt. A layer of gravel, preferably white or grey, is spread over the surface to protect it from the sun, which dries out the asphalt and causes it to lose its properties, and from temperature variations and hail, which damage it over time. Installing this type of asphalt requires the expertise of a professional roofer, as it is dangerous to handle molten asphalt, which emits a strong odour. Seasonal maintenance is required to add gravel as needed. Asphalt and gravel surfacing is relatively economical to install, but requires regular maintenance and has a shorter lifespan than its competitors, around 15 years (or more, depending on the quality of installation and maintenance). As a result, it is losing popularity for large roofs, and some municipalities are banning it because of its poor environmental impact.
Elastomeric bitumen coating
Used for some forty years in Quebec, elastomeric bitumen cladding consists of two elastomeric membranes in rolls: an underlayment and a granulated surface finishing membrane, available in several colors or in white, to ensure resistance to impact, tearing and sunlight. The underlayment is screw-attached or glued, while the finishing membrane is heat-installed. Joints are fusion-welded with a flashlight, fusing the underside of the membrane with the top of the underlay for a perfect seal. Installation is cleaner than with asphalt and gravel, but working with a flame involves certain fire hazards. It's advisable to find a good roofer with the necessary experience and insurance. Asphalt and gravel can also be cold-laid with self-adhesive strips. Increasingly used to replace asphalt and gravel as well as shingles on certain types of roofs, elastomeric bitumen coating costs 10% to 15% more, but has a lifespan of 25 to 40 years. Thanks to its elasticity, it is highly resistant to temperature variations, lighter, uniformly waterproof and easy to maintain. Care must be taken to ensure that water drains properly to avoid stagnant puddles and algae, which can shorten the life of the membrane by deteriorating the surface granules.
Single-layer synthetic membranes
More recent than the two previous options, single-layer synthetic membranes are a bit like a pool liner. Because they are laid in a single layer and the obstacles are chiselled away, they are mainly used in the commercial sector over large areas. There are two main types: EPDM (thermosetting rubber) and TPO (thermoplastic polyolefin). These membranes are highly resistant to sunlight, weather, temperature variations, bacteria, humidity and tearing, thanks to their exceptional elasticity. What's more, they're lightweight, recyclable and easy to install. TPO is mechanically fastened or hot-air welded. EPDM joints are sealed with contact adhesive or tape, and the membrane can be weighted down with a layer of gravel. In both cases, the membrane is installed over polyisocyanurate insulation panels to absorb impact. The challenge is to create perfect joints around the cut obstacles, otherwise watertightness may be compromised. Depending on the product chosen, life expectancy can range from 20 to over 50 years. The experts at Toitures Martin Lafleur install and repair asphalt, gravel and elastomeric bitumen coatings on residential and commercial flat roofs. Don't hesitate to call on them to ensure your roof looks impeccable and remains watertight!