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Installation - Things to Consider When Replacing a Low Slope Roof
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Energy Efficiency: More Than a Black and White Issue (RCI)
White Roofs, Green Myth? Good Marketing and Sloppy Science (Huffington Post)
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A Comprehensive Roof System Guide
There are many different flat roof systems to consider. Below is an extensive guide to assist you in reviewing your roofing options.
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Flat Roofing Systems
Following is an exhaustive guide of options we make available to the commercial, institutional, industrial, and residential marketplace.
1. Built Up (BUR) - "Tar and Gravel" - "Mop on"
2. Single Ply Membrane
a. EPDM Roofing
b. TPO Roofing
c. PVC Roofing
3. Modified Bitumen (SBS) "Torch On or Torch Down"
4. Low Slope Metal / Steel
5. Liquid Applied and Spray Foam
6. Green Roofing - Garden Roofs - Rooftop Decks, Patios, and Terrace Waterproofing
Multiple-Ply - Built Up (BUR) "Tar and Gravel"
Traditionally, flat roofs have been 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”. 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 Roofs are very flexible in application and have been an industry standard for many decades.
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 Roofing (Ethylene Propylene Diene Monomer)
EPDM 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 roofing is readily available in white, grey, or black. EPDM has competitive life cycle costs and 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 Roofing (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 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 is 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 roofing 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.
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.
TPO, reinforced and non-reinforced, is 100 percent recyclable during the production process. During production, if the need arises, the roof 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.
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 membranes are highly resistant to mold and algae growth, which can degrade the overall reflectivity of the roof and reduce anticipated energy savings.
[ source: ASTM Standards for TPO Membranes ]
PVC 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.
PVC has an established end-of-life recycling program that converts the old membrane back into roofing membrane products.
PVC is naturally fire retardant and will self extinguish with the removal of the flame source.
Reflective vinyl roofs (PVC) save 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.
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.
PVC meets all applicable building codes. PVC membranes also meet the cool roofing requirements of EnergyStar®, Green Globes™, and LEED®.
PVC roof membrane is inert and does not contribute any chemicals of concern to storm water runoff.
[source: sarka sarnafil]
2 Ply Modified Bitumen (SBS and APP)
These are asphalt-based materials, but plasticizers have been added to improve strength, flexibility, water-resistance, etc. They can be incorporated into a conventional BUR flat roof, 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 Bitumen 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.
Seamed Metal Roof
Low slope metal roofs have been chosen as a covering for commercial, institutional and industrial buildings for many years because of their ability to protect structures against the elements, to allow water to drain away from the surface, and to keep building contents and occupants dry and comfortable.
Metal roofs have a long service life, low life cycle cost, sustainability, recycle-ability, low maintenance, light weight and resistance to wind.
Low slope structural metal clad 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.
Study Substantiates Low Life Roof Cycle 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 roofing 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 Roofs Place Fewer Demands on Structure
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.
GRS uses Roof Coatings extensively for Metal Roof Restoration and Repair.
The Roof Coating section of our website has more information here:
The GRS Roofing Blog has numerous articles and information about roof coatings. When you arrive at the landing page of the blog, simply type in your search criteria in the search box in the right hand column of the blog page. For example, type in "roof coatings" or "liquid rubber roof". All pages that contain words you are searching will be listed at the top of the page as well as other pages linked to our roofing blog will be listed.
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.
By contrast, extensive has a shallow growing medium and the landscaping is designed to be more self-sustaining, requiring less maintenance than an intensive system. Extensive green roofs are less expensive than intensive systems, since they are lighter and require less structural support and need less frequent maintenance. The roof on Mountain Equipment Co-op in Toronto is an example of an extensive system, built in 1998.
New or Retrofit
Green roofs can be designed to be an integral part of a new building, or can be installed later on an existing building with several benefits. For example, the building is designed to provide the necessary structural support, and won't require reinforcement later. Also, the building can be designed to take advantage of the aesthetic value by providing viewing areas.
York University installed a 30,000 square foot green system during the construction of the Computer Sciences Building in 2003. This green system is not accessible. It has been monitored by the Toronto Region and Conservation Authority to determine the quantity and quality of storm-water and quantify other benefits of green roofs.
An example of a retrofit is the intensive 704m2 green roof on ESRI Canada Ltd. 12 Concorde Place. It covers 100% of available roof space on a commercial building, and it hosts 52 plant types including sedums, grasses, flowers, herbs, shrubs and trees.
Below is a brief description of a complete system that is more fully described in the consultant's report, Environmental Benefits and Costs of Green Technology for the City of Toronto.
In a complete green system, all parts are designed to support vegetation growth. These systems provide the most flexibility in terms of the type and nature of growing medium, drainage and protection layers and type of vegetation. Complete systems vary in thickness and weight from as low as 50mm to 75mm (2 to 3 inches) in depth and 60 to 90 kg per sq. m, (12 to 18 lbs per sq. ft.) in weight. They can be installed with a variety of membrane types.
Below is a brief description of a modular system that is more fully described in the consultant's report, Environmental Benefits and Costs of Green Technology for the City of Toronto.
Modular systems are essentially trays of vegetation in a growing medium that are grown off-site and simply placed on the roof to achieve complete coverage. They are available in different depths of growing medium typically ranging from 75mm to 300mm (3 to 12 inches). The variety of vegetation is typically more limited.
Re-cultivated vegetation blanket
Below is a brief description of a vegetation blanket system that is more fully described in the consultant's report, Environmental Benefits and Costs of Green Roof Technology for the City of Toronto.
A pre-cultivated vegetation blanket is a pre-grown interlocking green roof tile. The blanket shown below is available in a thickness of about 45mm (1.75 inches).
Blanket systems are available in a variety of system designs. The most versatile system contains 25 mm (1 inch) of planting substrate. The result is a lightweight system ranging in weight from 40 to 60 kg per sq. meter.
The majority of the vegetation is made up of several varieties of Sedum, a succulent plant (8.0 to 13.0lbs per sq. ft.) tolerant to extremes in temperature that survives with little or no irrigation while requiring very little maintenance. They are cultivated at ground level, then rolled and transported as a complete system on pallets or by crane.
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