Flat asphalt roofing has been installed since the 1840s. That is far longer than any single-ply roof system, most of which have been installed since the 1970s. The golden rule of asphalt roofing is that more is better. A 5 ply (or 5 layer) built-up or modified bitumen roof system, which may be ½” thick, will last far longer than any 2 ply (or 2 layers) built-up or modified system, which may be ¼” thick. In comparison, single ply systems are significantly thinner, typically between 45 millimeters (mills) (3/64 of an inch) to 80 mills (5/64 of an inch). Yet both roof systems have a similar life expectancy.
Single-ply has taken over the flat roofing industry over the years. Between the big 3 single-ply products, EPDM, TPO and PVC roofing, single-ply is installed on 86% of roofs throughout the United States. Asphalt, on the other hand, is installed on 14% of roofs. Some of the reasons for this shift include:
- Cost: As a rule of thumb, asphalt roof systems are far more expensive than single-ply roof systems. This is mostly due to the labor involved to install an asphalt roof system. Installing 3-5 plys, or layers, of asphalt roofing, takes far longer than installing 1 ply or layer of a single-ply roof system.
- Warranty: Typically, most single-ply roofing manufacturers offer a longer and more competitive warranty than asphalt roof manufacturers. Most single-ply manufacturers offer standard 15 to 20-year warranties, with some upgrades to get to a 25 or even a 30-year warranty. While some modified bitumen manufacturers do offer comparative warranties, they are installed at a far higher price point. A 30-year single-ply warranty still involves installing 1 layer of membrane. The membrane is thicker, the details are more extensive, and the cost is certainly higher. However, to install a 30-year asphalt warranty, 5 plys or layers of roofing are typically required, and the details are more extensive. This makes it a lot harder and more expensive to get the same warranty.
- Puncture resistance: Typically, asphalt roofing has a far better puncture resistance than any single-ply roof system. Installing multiple layers of thick asphalt roofing makes it much more difficult to puncture. Typically, when an old roof system needs to be removed, a single-ply roof removal is completed using utility knives. With an asphalt roof removal, 9 to 13 HP roof cutters are used, along with axes, chop saws, and other heavy-duty ripping equipment. However, single-ply manufacturers have gotten competitive by using thicker membranes (75, 80 and 90 mil membranes) and stronger, higher PSI cover boards. Additionally, some single-ply manufacturers are offering puncture-resistant warranties, which are not common on asphalt roof systems. While asphalt roofing still has better puncture resistance, single-ply is certainly durable enough that, in most cases, puncture resistance won’t be a problem.
- Flexibility: Single-ply roof systems are much more flexible. This is helpful particularly in regions where there are large temperature differences, such as New England. Extreme heat in the summer and extreme cold in the winter can be devastating to rigid asphalt flashing details. Most single-ply roof systems have the ability to expand and contract, making these temperature differences less problematic.
- Ease of Use: Single-ply roof systems are typically easier to install than asphalt roof systems. A contractor working on any system needs to understand the details and specifications to properly install a roof system, but typically single ply roofs have more standard details that are easier to follow. Plus, with the decline of asphalt roofing, it is getting harder and harder to find experienced workers that know how to install asphalt roofs. Flat asphalt roofing is almost becoming a lost art due to its less frequent use in the roofing industry.
The best roof system depends on the building’s use and the available budget. Asphalt roofing has far better puncture resistance and an exceptional track record. However, it also has a far greater cost and is much more difficult to install. Typically, the best price to performance is a single-ply roof system, which is why single-ply is dominating the flat roofing industry. However, if your roof system is prone to punctures, or you want a very proven roof system, a flat asphalt roof system may be a good choice.
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