Types of Commercial Roof Systems and Materials

Commercial Roof Systems

There are a multitude of commercial roofing systems available in the market today.

For the commercial building owner or facility manager, it can be difficult to navigate the terminology associated with the activity, and even more difficult to evaluate and understand the advantages and disadvantages of each water-proofing type.

First of all; commercial roof systems can be categorized in two types. Water-proofing for “flat or low slope “ applications, and water-shedding for steep slope areas.

Commercial roofing in Toronto involves both types of categories; and in general terms, could apply anywhere in Canada and the U.S.; with variations in methodology and product substitutions based on regional weather considerations.

The most common commercial roofing systems for flat roofs include the following:

B.U.R. (Built-Up Roof Systems)

B.U.R. (Built-Up Roof Systems), which typically involve the application of four plies of organic or five plies of fibreglass felts, inter-mopped with coatings of hot asphalt. A final pour of hot asphalt, and the spreading of clean pea gravel, are applied over the surface of the roof. This system has been the most commonly used for over 100 years in North America.

The advantages of such roof systems involved the fact that they can be self-healing to some degree. Asphalt used in such assemblies prior to 1977 was considered by many, to be superior to the asphalt manufactured today. The average life-span of such roofs is considered to be twenty years. Some older versions had been known to last thirty years. Such roofs had a higher concentration of coal tar pitch.

Disadvantages include high odour and pollution as a result of burning hot asphalt in kettles. Such assemblies are not considered to qualify as “cool roof” assemblies, as they can retain heat, and are considered to contribute to the urban heat island effect. Special equipment, highly qualified labour, and considerable experience, are necessary to install such systems well.

Modified Bitumen Systems

Modified Bitumen Systems (often nick-named rubber roofs), were originally introduced to the North American market as single ply systems, which required a reflective paint coating to be applied after installation. The product’s evolution resulted in a two-ply system of application. Modern two-ply modified bitumen systems can be applied by using hot asphalt, cold applied asphalt, or torch applied methods.

The system typically involves the application of a base ply having a smooth surface, and finished ply, referred to as a cap sheet. The cap sheet has a ceramic granular coating embedded in the top surface, (much like shingles). Advantages include the fact that they are lighter systems than B.U.R., have a higher tensile strength, and have the ability to expand and contract with the thermal movement of a building.

The quality of installation is key, as proper methodology and techniques are required to heat weld the membranes together. Over –torching of the materials can lead to premature failure, and or insufficient bleed out on lap seams, are often causes of premature failure of such systems.

Other advantages include that they are easier to repair than traditional BUR, involving less labour and equipment setups. Because modified bitumen membrane systems are lighter, they can provide an advantage in terms of the increased load that a roof may withstand, such as snow for example.

Modified bitumen commercial roof systems have been used in North America widely for over thirty years, and even longer in Europe.

TPO Flat Roof Membranes

TPO Flat Roof Membranes (Thermoplastic polyolefin), were designed specifically for commercial / industrial roof applications. Essentially, think of large bales of a vinyl appearance material; which is installed almost like carpet over the roof. Such roofing assemblies are considered “cool roof” systems.

As a result of their white reflective surface; TPO reflects heat from the rooftop and is therefore known to result in lower heating and cooling costs for commercial structures; particularly when incorporating higher degrees of thermal insulation beneath the assembly.

Such membranes can be fully adhered with an adhesive in the field of the sheets (termed a fully adhered assembly); or the system can be loose laid allowing for greater expansion & contraction with building movement. In all systems, plates and screws are used along lap seams in prescribed numbers and patterns to secure the material. Overlapping material seams are then thermo-fused (hot air welded); using robotic hot air welders in the field runs of the sheeting, and hand-held hot air welders at detail areas such as pipe protrusions, etc.

Such materials are typically available in 45 mil, 60 mil, and 80 mil configurations. TPO is increasingly taking market share for commercial roofing systems, because it provides many advantages. It is easily repaired, involves fewer seams than modified bitumen, and is lightweight relative to other assemblies. It requires no open flame application, so it is considered safer for many structures. TPO is also a fully recyclable material.

TPO is being embraced by cities such as New York, Chicago and Toronto; who are attempting to curb the Urban Heat Island Effect. In other words, lowering the ambient temperature in cities by several degrees, which results in less energy consumption, and a more sustainable living environment.

In cities where high rise buildings are prevalent; firefighting issues can be a consideration, as open flame applied roofing materials have created issues for fire control. TPO is also a great candidate for green roofing application, as it does not rot like organic based materials can, being prone to do so, under conditions of stagnant water.

EPDM (Ethelyne Polymer Dienne Monomer)

EPDM (Ethelyne Polymer Dienne Monomer) is also considered a single-ply commercial roofing system membrane. Similar in appearance to a bicycle tube material, it is also available in various thicknesses.

Deemed a highly cost-effective flat roofing solution, in terms of initial cost of installation; EPDM can be less puncture resistant if applied as a loose-laid assembly. Loose- laid EPDM is typically ballasted using heavy river wash stone. It can also be applied using hot asphalt, if “felt-backed” EPDM is used. EPDM can also be fully adhered using adhesives.

White or grey EPDM can also qualify as a cool, roof assembly. Overlapping seams are first cleaned to remove talc,then are adhered with such items as seaming tape, and or adhesives designed for the product.

PMR Roofing Assemblies 

PMR Roofing Assemblies (Protected Membrane Systems) also know as inverted, or upside down roofs; can consist of many of the systems described above, as the water-proofing component. The difference between “conventional” flat roof systems and PMR systems, is where the thermal roofing insulation is placed.

In PMR assemblies; the waterproofing membrane is applied to the roof substrate (deck), and the insulation is exterior to the waterproofing membrane. Extruded polystyrene (rigid) insulation is used in such assemblies because the insulation does not rot with long-term exposure to water. The insulation is a shiplap design, and is typically covered with a fabric filter cloth, and then ballasted with heavy, smooth river rock to act as ballast. Such systems are usually found on buildings that have concrete roof decks (substrates).

In conventional flat roof applications; the thermal insulation is placed beneath the waterproofing membrane. Polyisocyanurate (Poly-Iso) insulation is typically used for today’s modern flat roof assemblies.

Green Roof Systems

Green Roof Systems refer to creating an eco-system on a flat roof, usually involving a variety of sedums that bloom through various seasons, and then go dormant in winter months (eastern Canada and the US).

Green roofs have existed in Europe for decades, and have been a more recent phenomenon in North America. Over the past decade, popularity and demand for green roofing has been steadily increasing.

For some, the initial investment can be prohibitive; but over time the investment can represent tremendous value in terms of increasing the longevity of the actual roof assembly, mitigating stormwater run-off in major cities, helping to increase thermal value, and in turn helping to lower heating and cooling costs, and creating a mini ecosystem for birds and insects. Generation of clean oxygen, and lowering the temperature in major cities also helps to reduce the effects of pollution; both air and noise.

A prerequisite for installing a green roof, first involves selecting a suitable water-proofing assembly for the flat roof, and then testing to insure that it is well installed; prior to applying the plant materials.

Green roofs are termed in two different categories. Extensive and intensive systems. Extensive systems are typically lighter weight, and consist of a sedum matt applied over a fleece layer for water retention. Beneath the fleece layer, is a polyethylene root barrier sheet, used to isolate the water-proofing membrane from the growing medium assembly. It can be thought of, like laying sod. It is best to combine a variety of sedum mixes which can thrive in various weather conditions, and to pick materials which can be drought resistant.

Intensive systems could be characterized almost like container gardening. Plant varieties are placed in grids of trays or pots. Such systems are usually heavier and perhaps better suited to roofs which have concrete decks or that have substantial structural load capability.

Typical design considerations involve retaining an engineer whom can study the existing roof structure and determine load restrictions, or who can design enhanced load capability for the roof’s structure if required. Permits and plans are usually involved when designing such assemblies.

Maintenance must also be considered, as under drought conditions, the building owner must make provision for watering. Access and fire considerations should be particularly considered on taller roof structures. Examples can be the requirement for paver walkways, railing systems, and proper clearances from the roof’s edge, for those whom may be maintaining the green roof.

To learn more about commercial roofing, green roofing, and other related building envelope services; contact AVENUE ROAD ROOFING®