What is the best flat roof?

Flat Roofing

Flat roofing is a vital part of the building and thus a substantial and critical investment.

Whether you are considering the environmental benefits of green / sustainable “cool roofing membranes”, a conventional flat roof system, rooftop deck, or are looking for ways to extend the life of an existing flat roof, our expertise and commitment to quality will ensure your system will be built to last and will extend the life of your building.

Flat Roofing install

No roof will last forever – not even the very best installed by the very best flat roofers. A re-roof or retro-fit can help maintain a healthy building and your valued investment. The full-removal (replacement) of a low-slope roofing system involves removal of the surface membrane and insulation to the deck to enable installation of the new system.

A Recovery (retro-fit, overlay, re-covering) involves covering an existing system with a new roof membrane. This process requires removal of all wet, damaged, or deteriorating roofing insulation prior to the new low-slope roof being installed. Both methods are appropriate for flat roof systems that can no longer be repaired through regular maintenance, are showing signs of serious deterioration, or are regularly leaking.

New Flat roofs Installations

Flat roofs are not installed in a controlled environment – projects have many variables. The type of roofing material, application, job-site conditions, and weather all affect a construction project.

Flat Roof Systems

Flat Roof Repair. Materials and Option to Choose From.

Following is an exhaustive guide of roofing options we make available to the commercial, institutional, industrial, and residential marketplace.

1. Built Up (BUR) – Tar and Gravel Flat Roofing (Mop on)

2. Single Ply Roof Membrane

a. EPDM Roof

b. TPO Roof

c. PVC Roof

3. SBS Modified Bitumen Flat Roof (Torch-On or Torch Down)

4. Metal / Steel Roof (Low Slope)

5. Liquid Applied and Spray Foam Roofing

6. Green Roof – Garden Roofs – Rooftop Decks, Patios, and Terrace Waterproofing

Multiple-Ply – Tar and Gravel Roof

Traditionally, low slope roofs were installed by setting 3-4 layers of asphalt-saturated felt (tar-paper) by mopping hot asphalt. Typically, the surfacing is gravel set in a flood-coat of hot asphalt. This is referred to as “conventional built-up, BUR, or Tar and Gravel roofs”. GRS installs new Tar and Gravel and regularly repairs and maintains Tar and Gravel roofs that have been installed 50 or more years ago. Tar and Gravel is very flexible in application and have been an industry standard for many decades.

Single-Ply Roof Membranes

Over the years, a wide variety of flat roof membranes have been developed, using various forms of synthetic rubber and vinyl. The membrane is manufactured under controlled factory conditions. The seams are formed on site, using adhesives, tapes, or hot-air welding. Some are available in different colors and can be manufactured in wide rolls to minimize seams.

EPDM Roof (Ethylene Propylene Diene Monomer)

EPDM roofing is a single ply system composed of a rubber membrane used on commercial, industrial, and residential projects. It is applied using a fully-adhered glue system, loose-laid with gravel (ballasted), or mechanically fastened – all of which require no open flame. The environmentally friendly considerations of EPDM are; reduced emissions from equipment, fewer petroleum based products and less landfill waste. EPDM can lower heating and cooling costs with proper insulation. EPDM is readily available in white, grey, or black. EPDM has competitive life cycle costs. It is an excellent choice for retro – fits with less cost than completely replacing the whole roof assembly. EPDM has been installed on millions of square feet over a number of decades and is widely used today.

TPO Roof (Thermo-plastic Polyolefin)

A thermoplastic elastomer is a diverse family of rubber-like materials that unlike conventional thermoset rubbers, can be reprocessed and recycled like thermoplastic materials. Thermoplastic polyolefins are in the thermoplastic elastomer family and are commonly referred to as TPO.

TPO roof membranes are used in various commercial, industrial, and residential applications, including the automobile industry, and have seen their usage expand. Over time, TPO moved into the roofing industry as a non-reinforced sheet. In 1993, the original non-reinforced TPO was replaced with membranes containing reinforcing fabric. TPO installation has grown to hundreds of millions of square feet annually.

TPO Composition

TPO roofs are typically based on polypropylene and EP (ethylene-propylene) rubber polymerized together using state-of-the-art polymer manufacturing technology. This technology enables the production of TPO membranes that are flexible at low temperatures without the use of polymeric or liquid plasticizers. Unlike some other popular thermoplastic roof membranes, the TPO polymer does not contain chlorine and no chlorine-containing ingredients are added during sheet production. This lack of chlorine has allowed TPO marketers to tout their membrane as an environmentally safe, “green” product.

The TPO resin is compounded with other components including a weathering package, fire retardants and pigments for color to create a product that can withstand the elements associated with rooftop exposure. The membrane is comprised of TPO based top and bottom plies encapsulating a reinforcing fabric that enhances the physical properties of the sheet. The combination of the fabric and TPO plies provide reinforced roofing membranes with high breaking and tearing strength and puncture resistance.

TPO System Types

TPO is typically installed using mechanical fasteners and plates placed along the edge of the sheet and fastened through the membrane and into the decking. Adjoining sheets of TPO are overlapped, covering the fasteners and plates, and joined together with a hot air weld. In the field area, proper membrane width and fastener spacing is determined after calculating potential uplift loads based on building height, surrounding terrain and the wind zone in which the building is located.

The fastener/deck combination must exhibit adequate pull-out resistance to withstand the fastener loading generated during uplift. The membrane and the welded seam must also resist the forces generated by wind uplift. The ability of a mechanically fastened system to withstand these forces is typically evaluated using a 3.7 x 7.3 m (12 ft x 24 ft) uplift table where the system may be pressurized until failure. Along the perimeter of the roof, where the highest wind loads are experienced, reduced width membrane (40 to 60 percent of the field sheet width) is installed to reduce the fastener and seam loading.

TPO may also be fully adhered to an insulation or deck material using an adhesive. Insulation is typically secured to the deck with mechanical fasteners and the TPO is adhered to the insulation.

This type of system is highly resistant to wind and its associated uplift forces. Since the sheet is 100 percent affixed to the substrate, the membrane does not flutter due to associated wind forces. With no sheet movement due to the 100 percent attachment of the membrane, the fully adhered system is ideal for very visible roofs such as domes or other high slope applications.

Weld-ability: One of the primary benefits of TPO is the ability to fuse the sheets together with a hot air weld. The welding process results in a bond that is actually stronger than the sheet itself. Roof flashing details, such as exhaust vents, pipes and parapet corners are also completed using hot air welds and flashing material (typically non-reinforced).

When properly compounded, TPO has a wide window of weld-ability, allowing the applicator to complete hot air welds consistently in a broad temperature range.

TPO is a thermoplastic material and does not “cure” on the rooftop once installed. This allows the sheet to be repaired with proper surface preparation after rooftop exposure.

Recycling: TPO, reinforced and non-reinforced, is 100 percent recyclable during the production process. During production, if the need arises, the roofing membrane can be ground into “rework” and this regrind can be incorporated into the bottom ply during the extrusion process to produce new TPO product. This process results in 100 percent reuse of recycled product.

Reflectivity: Another important characteristic of TPO is its high level of reflectivity. Because of this, white TPO can meet and even substantially exceed ENERGY STAR performance levels. While TPO membranes typically display reflectivity ratings in the high 80 percent range when new (ENERGY STAR specifications require 65 percent minimum) and in the low 80 percent range after three-year rooftop exposure with cleaning (ENERGY STAR specifications require 50 percent minimum). TPO roof membranes are highly resistant to mold and algae growth, which can degrade the overall reflectivity of the roof and reduce anticipated energy savings.

PVC Roof (Poly Vinyl Chloride)


PVC roofing is among the most durable waterproofing options as proven through more than 45 years of service on roofs all over the world. PVC products serve their intended purpose for a long period of time without need for replacement are naturally more sustainable. Recycling: PVC has an established end-of-life recycling program that converts the old membrane back into roofing membrane products.

Fire Safety: PVC is naturally fire retardant and will self extinguish with the removal of the flame source. Energy Efficiency: Reflective vinyl roofs (PVC) saves energy by reducing the absorption of solar energy and transfer to the building interior. Less heat transferred to the interior means less energy needed for air conditioning.

Resource Efficiency: Just 47% of the PVC resin’s raw materials are derived from petroleum, less than any other single ply membrane. The remaining 53% for PVC are derived from salt. Health & Safety: PVC is inert and contains no dioxins. The plasticizers are highly stable and an integral part of the PVC membrane. They have never been shown by any government body to be harmful to humans.

Code Compliance: PVC meets all applicable building codes. PVC membranes also meet the cool roof requirements of EnergyStar®, Green Globes™, and LEED®. Water Quality: PVC roof membrane is inert and does not contribute any chemicals of concern to storm water runoff.

2 Ply Modified Bitumen Roof (SBS and APP)

These are asphalt-based materials. Plasticizers have been added to improve strength, flexibility, water-resistance, etc. They can be incorporated into conventional BUR flats, or applied as a single-ply membrane. Close cousin of the Built-up-Roof (BUR). Engineered modified bitumen originated in Europe in the mid 1960’s and have become a standard application – used successfully in the United States and Canada since approximately 1975.

Increased resistance to brittleness at cold temperatures, greater flow resistance at high temperatures, and increased elasticity can be achieved by blending synthetic rubberized polymers with asphalt in lieu of modification by the blowing process used for BUR asphalt.

There are numerous surfacing options for this system which include a factory applied mineral surface, gravel surface, including “cool roof” coatings which are highly-reflective to save on building cooling costs. Mineral-surfaced roofing products are typically furnished with white granules, but are also available in designer colors to match asphalt shingles or to otherwise compliment the over all building design.

It gives system designers and installers an even broader array of options than with BUR. It may be installed by the torch-application method, or “hot-mopped” like BUR, or applied with “cold-process” adhesives.

The latest innovation to modified is the self-adhering sheet. Using special combinations of polymers to modify the underside of the sheet, the rolls are manufactured with a release paper. The installer removes the release paper and as the sheet is rolled out, it adheres itself to the substrate. This method eliminates the risks associated with the use of torches, hot asphalt, and is completely free of VOC (volatile organic chemicals) fumes during and after roof application.

Benefits of Modified Roofing Membranes

Proven track record of performance in Commercial, Industrial, and Residential applications. Superior waterproof characteristics. Broad range of roof application methods. Wide choice of roof top-surfacing, including “Cool Roofing” options. With insulation, provides an even better-performing building component. High tensile-strength. Available as part of a fire, wind, and/or hail rating system. Competitive roof life-cycle cost. Available with flame-free and VOC-free installation. Long-term rmanufacturer warranties are available.

Metal Roofing

Low slope metal roofs have been chosen as a covering for commercial, institutional and industrial buildings for many years. A metal roof protects structures against the elements, allows water to drain away from the surface, and keeps building contents and occupants dry and comfortable.

Metal roofing has a long service life, low life cycle cost, sustainability, recycle-ability, low maintenance, light weight and resistance to wind.

Low slope structural metal clad roof systems (generally used on roof pitches ranging from ¼:12 to 3:12), consist of interlocking roof panels. Commonly called standing seam the seams run vertically along the roof surface. These roof panels generally come with a painted mill finish or a clear acrylic finish. Some metal used on low slope roof applications requires machine seaming during installation to ensure a watertight seal. A seaming apparatus is rolled along the panels to crimp the panel seams together.

A standing seam roof design assures adequate drainage from rain and snow, effectively eliminating ponding, leaks and related problems associated with built-up roofs. In retrofit projects, a sub-framing system is attached to the existing roof surface to provide a minimum ¼:12 roof pitch.

Low slope metal roofs are not prone to the degradation experienced by organic materials, enabling them to better resist the elements. This, in turn, results in a longer life span and a very low annual operating cost.

Metal Roof Cost

As a result of the durability and reliability of these systems, low slope metal roof manufacturers offer 20- to 40-year warranties on their products. Their long life and low maintenance requirements also put metal roofs on a very attractive life cycle cost track.

This was confirmed in a 2005 study of low slope roofs conducted by Ducker International. Respondents to the study said they expected the life cycle cost of a metal roof, including outlays for maintenance, to be about 30 cents a square foot per year, far less than their expectations for built-up and single-ply roofs, at 37 cents and 57 cents, respectively.

Metal roofs also have a significantly longer expected service life than either built-up or single-ply roofs. Study participants said they expect metal to last 40 years – 17 years longer than built-up and 20 years longer than single-ply.

Not only can low slope metal contribute to the bottom line, it can also contribute to LEED credits, which are awarded to buildings that use high recycled content and other “green” construction material. A typical low slope metal roof has at least 25% recycled content, and at the end of its long useful life is 100% recyclable. In addition, “cool roofing” can significantly reduce a building’s long term energy use. With heat deflecting metal coatings, energy costs can be reduced up to 40% or more, according to a study conducted by Oak Ridge National Laboratory.

Metal roofing systems

Typically, low slope metal roof systems vary in weight from 40 to 135 pounds per 100 square feet, making them among the lightest roofing products and the easiest to install. A lightweight roofing system also places fewer demands on a building’s structural support system, an important consideration in earthquake-prone areas.

Unlike non-metal systems which require an underlying substrate or deck, low slope metal roofs can be applied directly over bar joists or purlins. And, because of their interlocking or active fastening systems, metal roof panels are designed to meet the requirements of severe wind and uplift tests.

Metal roof panels come in a variety of materials as well as many colors, textures and profiles. To ensure longer life, almost all low slope roof materials are protected from the elements by high performance, highly durable metallic coatings.

Liquid and Spray-Applied Roof Coatings

A wide variety of liquid applied systems are available that can be applied with roller, squeegee, or spray. Some incorporate a reinforcing fabric bedded in the liquid. These systems are sometimes used as a coating over an existing roof. Their use also extends to various commercial and industrial applications including; parking decks, balconies and terraces, waterproofing, etc.

Polyurethane Foam Roofing (SPF) is a closed-cell material formed by combining two liquid components. When these two materials meet in the mixing gun, they expand 20 to 30 times their volume immediately, forming rigid polyurethane foam (PUF). This foam is sprayed on the entire roof to the desired thickness, usually 1-2 inches, to form a seamless monolithic surface including flashing, penetrations and parapet walls. This eliminates seams and cold joints, the primary source of major roof leaks, and provides a durable waterproof covering that bonds tightly to nearly any properly prepared surface.

Sprayed Polyurethane Foam is lightweight – about 8 ounces per square foot – and can be applied over most existing roof structures without exceeding the structural load capacity. Yet it is strong, easily withstanding foot traffic and other weight requirements. Since it can be applied directly over asphalt, shingles, built up roofs, clay, concrete, metal and wood there is little to no need for tear-off, reducing the amount of roof installation time, disruption to the business and even reducing the debris in landfills.

Sprayed Polyurethane Foam has to be protected from exposure to the sun’s ultra-violet radiation and moisture. This is where roof coatings help protect and seal the foam from any damage.

Green Roofing

A green roof is an extension of an above grade roof, built on top of a human-made structure, that allows vegetation to grow in a growing medium and which is designed, constructed and maintained. A green roof assembly includes, as a minimum, a root repellent system, a drainage system, a filtering layer, a growing medium and plants, and is installed on a waterproof membrane of an applicable roof.

There are three main types of green roof systems:

1. Complete systems where all the different components including roof membrane are an integral part of the whole system.

2. Modular systems that are positioned above the existing roofing system.

3. Pre-cultivated vegetation blankets that consist of growing medium and plants that are rolled onto the existing roofing system with drainage mats and root barriers as required

Intensive or extensive
Intensive/active green roofs have a deep growing medium that supports a variety of landscape design and growth. They are accessible and used as recreational space. An example of an intensive/active green roof is the Manulife Centre which is located over a parking garage. It is a well established 25 years old system with mature trees that reach three stories high.


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