A description of Roofing Types
Asphalt is an aliphatic compound and in almost all cases a byproduct of the oil industry. Some asphalt is manufactured from oil as the intended purpose, and this is limited to high quality asphalt produced for longer lasting asphalt built-up roofs. Asphalt ages through photo-oxidation accelerated by heat. As it ages, the asphalts melt point rises and there is a loss of plasticizers. As mass is lost, the asphalt shrinks and forms a surface similar to alligator skin. Asphalt breaks down slowly in water, and the more exposure the more rapid the degradation. Asphalt also dissolves readily when exposed to oils and some solvents.
There are four types of roofing asphalt. Heating and blowing with oxygen create each type. The longer the process the higher the melt-point of the asphalt. Therefore, Type I asphalt has characteristics closest to coal tar and can only be used on dead level surfaces. Type II, is considered flat and can be applied to surfaces up to 1/4 in 12 slopes. Type III, is considered to be "steep" asphalt but is limited to slopes up to 2 in 12, and Type IV is "special steep". The drawback is, the longer it is processed, the shorter the life. A dead level roof where Type I asphalt was used as the flood and gravel adhesive has performed nearly as well as Coal Tar. Asphalt roofs are also sustainable by restoring the lifecycle by making repairs and recoating with compatible products. The process can be repeated as necessary at a significant cost savings with very little impact on the environment.
Asphalt BUR is a common roofing type for flat roofs and is hardly used anymore. It is made up of multiple layers of reinforcing plies and asphalt forming a redundancy of water proofing layers. The reflectivity of built up roofs depend on the surfacing material used. Gravel is the most common and they are referred to as asphalt and gravel roofs. Asphalt degradation is a growing concern. UV-rays oxidize the surface of the asphalt and produce a chalk-like residue. As plasticizers leach out of the asphalt, asphalt built up roofs becomes brittle. Cracking and alligatoring inevitably follows, allowing water to penetrate the system causing blisters, cracks and leaks. Compared to other systems, installation of asphalt roofs is energy-intensive (hot processes typically use LP gas as the heat source), and contributes to atmospheric air pollution (toxic, and green-house gases are lost from the asphalt during installation).
Ethylene Propylene Diene Monomer is a synthetic rubber most commonly used in single-ply roofing because it is readily available and relatively simple to apply. EPDM as a roofing membrane has advanced significantly over recent years. Problems previously associated with it included moisture gain under the membrane by vapor drive (occurring on roofs with air conditioned space beneath), and that EPDM did not like to adhere to itself and seam problems occurred. Simply adding a vapor barrier, such as a DPM will resolve vapor drive.
Seaming has become simple with the addition of Factory Applied Tape, resulting in fast installation & perfect joins every time. The addition of these tapes has reduced labor by as much as 75%. Rolls of EPDM are available with Factory Applied Tape pre-applied to one edge. This is an uncured EPDM tape. The other edge is marked to indicate the appropriate overlap. The Factory Applied Tape is laid into the primed overlap and rolled with a little pressure. The resulting seam is stronger, neater and highly unlikely to fail. Any details are taken care of with the appropriate tape. The process involves applying primer with a brush, allowing it to flash off to touch dry (this takes moments), then applying the tape and rolling to ensure it’s watertight. It’s a low cost membrane, but when properly applied in appropriate places. Typically, there are three installation methods. Ballasted at 1,000 lbs/sq or 10 lbs/sq.ft. with large round stones. Mechanically attached is another method and is suitable in some applications where wind velocities are not usually high. Fully adhered is the most expensive installation method but proves to give the longest performance of the three methods.
The new generation of EPDM, FleeceBack, has been combined with a polyester fleece backing and fabricated with a patented adhesive technology, which provides consistent bond strength between the fleece backing and the membrane. This has resulted in largely eliminating shrinkage of the product, whilst still allowing it to stretch up to 300% and move with the building through the seasons. The fleece improves puncture and tear resistance considerably and .045 mil EPDM with a fleece backing is 180% stronger than .060 mil bare EPDM.
PVC (vinyl) membrane roofing
Polyvinyl Chloride (PVC) membrane roofing is also known as vinyl roofing. Vinyl is derived from two simple ingredients: fossil fuel and salt. Petroleum or natural gas is processed to make ethylene, and salt is subjected to electrolysis to separate out the natural element chlorine. Ethylene and chlorine are combined to produce ethylene dichloride (EDC), which is further processed into a gas called vinyl chloride monomer (VCM). In the next step, known as polymerization, the VCM molecule forms chains, converting the gas into a fine, white powder – vinyl resin –, which becomes the basis for the final process, compounding. In compounding, vinyl resin may be blended with additives such as stabilizers for durability, plasticizers for flexibility and pigments for color.
Thermoplastic PVC roofing is extremely strong, as its heat-welded seams form a permanent, watertight bond that is stronger than the membrane itself. PVC resin is modified with plasticizers and UV stabilizers, and reinforced with fiberglass non-woven mats or polyester woven scrims, for use as a flexible roofing membrane.
Vinyl roofs are inherently fire resistant due to their chemical composition and have a broader range of fire ratings over common substrates. PVC has been sold for commercial roofing use for more than 40 years. Vinyl roofing membranes’ long life cycle – and the associated lower energy consumption to both produce the raw material and process it into useful products – is a significant factor in their sustainability as a building product.
Vinyl roofs provide an energy-efficient roofing option due to their inherently light coloring. While the surface of a black roof can experience a temperature increase of as much as 90 degrees under the heat of the full sun, a white reflective roof typically increases only 10-25 degrees Fahrenheit.
Vinyl membranes can also be used in waterproofing applications for roofing. This is a common technique used in association with green, or planted, roofs.
Thermoplastic Polyolefin single-ply roofing roof membranes constructed from ethylene propylene rubber. This roofing material can be fully adhered, mechanically fastened, or balasted with the proven performance of hot-air weldable seams. The material's manufacturers are so confident in properly welded seams that the material is sometimes advertised as a monolithic (seamless) roof. Seam strengths are reportedly 3 to 4 times those of EPDM's adhesive and tape seams. TPO is highly resistant to tears, impacts, and punctures with good flexibility to allow for building movement.
This is a popular choice for "Green" building. It is available in white, grey, and tan. Using white roof material helps reduce the "heat island effect" and solar heat gain in the building. They have been tested as having excellent resistance to ozone, are algae-resistant, environmentally friendly and safe to install.
Cold applied liquid membranes
A popular choice for roof refurbishment this roofing type can provide seamless waterproofing around roof protrusions and details. And can provide a reflective coating for the entire roof.
Polyurethane Foam Roofing
This roofing system does not work in New England and at DAVOL we remove the style roofs all the time. The Polyurethane foam is a coated style roof with white, elastomeric coating, sprayed on polyurethane roofing it will need re-coats at 5 years, 25 years, and every 20. These roofs provide a thermal barrier that has no air infiltration and can retain water if the coating has a failure, Contact DAVOL for an evaluation of your roof if you think this is the type of roof your building has.
Coal-Tar Pitch Built Up Roof
DAVOL will not install this dangerous type of roofing system, coal tar pitch is a known carcinogen, and forbidden by code in many areas, and even where permitted it should be avoided where possible, due to health concerns. In patching existing coal tar roofs, worker and building occupant exposure should be avoided, or minimized to the maximum extent possible. Coal Tar fumes are hazardous and provisions must be made during application to prevent fumes from getting into the building. Workers should wear protective equipment and clothing, and commonly get higher compensation (Pitch Pay) for exposure to the health risks.
Coal Tar is an aromatic hydrocarbon and a by-product from the coking process of the coal industry. It is historically in abundance where coal is used in steel manufacturing. It ages very slowly through volatilization and is an excellent waterproofing and oil resistant product. Roofs are manufactured by heating the coal tar and applying between layers of coal tar saturated felts. It has limitations to application on dead level or flat roofs with slopes less than 1/4 in 12. It has a tendency to soften in warm temperatures and "heal" itself. It is always ballasted with gravel to provide a walking surface. Coal Tar provides an extremely long life cycle that is sustainable and renewable. It takes energy to manufacture and to construct a roof with it but its proven longevity with periodic maintenance provides service for many years, with ages from 50 to 70 years not uncommon, with some now performing for over a century.
Coal tar pitch is often confused with asphalt, and asphalt with coal tar pitch. Although they are both black and both are melted in a kettle when used in roofing, that is where the similarity stops.