Anatomy of an Industrial Flat Roof

Flat Roof on a Self Storage Building

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 industrial building will be used.

For example, the roofing 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 industrial flat roof from the bottom up to the top surface.

Roof section diagram Anatomy of a Flat Roof


Industrial Flat Roof Deck

The roof deck, or substrate, is the weight-bearing layer of your flat roof system.  It 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. 

Industrial Flat Roof Vapour Retarder

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. 

Industrial Flat Roof Insulation

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 is installed over 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.

Industrial Flat Roof Cover Board

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. 

Industrial Flat Roof Membrane

The top layer on a commercial flat roof is the roof membrane.  This is 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).

Anatomy of a Flat Roof Modified Bitumen roof in Toronto
Modified Bitumen roof membrane

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, is one of the oldest membrane systems.  It 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. This is 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.  

Anatomy of a Flat Roof BUR Roof in Toronto
Hybrid built-up roof membrane (BUR)

Single-Ply Membranes: 

TPO (Thermoplastic Polyolefin), PVC (Polyvinyl Chloride) and EPDM (Ethylene Propylene Diene Terpolymer) are single-ply options. These are chosen by a roof designer to achieve specific requirements, let it be: resistance to chemicals or hot application methods or reflectivity factors.


The First Step to Designing and Building Your Industrial Flat Roof

Knowing about an industrial 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. One that is recognized for superior workmanship and customer service.

Contact Elite Roofing in the Greater Toronto Area to install or repair your industrial flat roof.