The ins and outs of industrial flat roofing can be complicated, especially in Toronto or other areas with harsh climates. The primary guidepost in determining what type of roof to choose is how the building will be used. For example, the needs of a food processing plant are very different from those of a warehouse or community center.
No matter the purpose of your building, all roofs have similar elements, but with many variations. Making the right choices for your flat roof project will increase the longevity of the building and the safety of the people, equipment, and inventory inside.
Below, we’ll discuss the roof from the bottom up to the top surface.
The roof deck, or substrate, is the weight-bearing layer of your flat roof system that sits on appropriate structural supports, carrying the roofing materials built above it. The most common types of decking are steel, poured or precast concrete, wood, and composite decks.
Selected based on the type of deck and building use considerations, it is usually a thin and flexible layer installed over the decking to minimize moisture penetration from inside of the building up into the roofing assembly. Moisture migration from inside is as bad for roofing components as leak from the outside. The vapor retarder needs to be on the warm side of the roof assembly. On a refrigerated warehouse or ice rink, the warm side is on top of the roof so different considerations apply.
In Toronto’s cold winter and warm summer weather, improving insulation Rvalue reduces energy costs. This main insulating layer is often chosen to suit the type of roof deck it will be installed over and the other components of the selected roofing system. The most common type of insulation currently used in Ontario is open cell polyisocyanurate [ISO]. On the other hand, inverted or protected membrane roof assemblies typically have closed cell insulation, such as extruded polystyrene [XPS], in place of ISO. Closed cell insulation will float in water, whereas open cell insulation will sink.
Cover boards, which are installed on top of the main insulation board, provide a stable and smooth surface for new membrane installation. Varieties of cover board include perlite, fibreboard, asphalt protection board, cementitious board, and gypsum board. Some of the important considerations when selecting a cover board for your flat roof include the method of attachment, roof traffic or use of the roof area for amenity space or solar PV systems.
The top layer on a commercial flat roof is the roof membrane, the watertight seal that protects the internal structure from weather, wind, abrasion, roof traffic, and other weathering factors. The three main types of membranes are Built-Up Roofing (BUR, including 3 and 4 ply asphalt and gravel), 2 ply SBS modified bitumen and single-ply (TPO, PVC and EPDM).
While some design criteria or installation elements of these two types of systems are similar in certain ways, there are also some key differences.
Built-up Roofs (BUR):
BUR, one of the oldest membrane systems, consists of installing multiple interplied layers of organic or glass type reinforced felt in a hot mopping of asphalt. These layers are covered with aggregate surfacing, most commonly with 3/8” pea gravel to form a final integrated roof membrane. A gravel top coat installation is optional in two ply modified bitumen membrane systems due to the fact that the top cap sheet layer can have ultraviolet resistant, ceramic stone granules that are factory embedded to the top surface.
TPO (Thermoplastic Polyolefin), PVC (Polyvinyl Chloride) and EPDM (Ethylene Propylene Diene Terpolymer) are single-ply options chosen by a roof designer to achieve a specific requirement, let it be: resistance to chemicals or hot application methods or reflectivity factors.
The First Step to Designing and Building Your Roof
Knowing about a roof’s anatomy is a basic step in understanding how to work with your architect, contractor, and roofing professionals. Whatever your final specifications, be sure to work with an experienced, reliable roofing company that is recognized for superior workmanship and customer service. Contact Elite Roofing in Toronto and surrounding areas to install or repair your commercial flat roof.