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Low Slope Roofing Options

Traditional flat roofing systems include built up, modified bitumen and single ply. Another option gaining market share for their economic benefits are Liquid Applied Roofing Systems (See also: Understanding Liquid Applied Roofing Systems). It is important to note that the information on this page can vary from one manufacturer to the next and may change from time to time.

Low slope roofing is rated anywhere from 10-30 years by the various product manufacturers. The determination of this longevity is how the new roof is installed. One thing is for sure, though, a low slope roofing system is all about the details. Neglect one detail and it’ll leak for sure!

Single Ply – TPO Low Slope Roofing Options

TPO is short for Thermo-Plastic Olephine and is quickly becoming the standard for low slope roofing applications in the Chicago and Northern Illinois area. TPO is a highly reflective and durable single ply membrane. What makes TPO great is its’ ease of installation and it’s heat welded seams.

Hot air, forced from electric heaters, are used to fuse flashings and seams. In addition TPO is available in rolls larger than more traditional roofing systems meaning less seams. Less seams means less chance for failure. TPO is and excellent choice where minor ponding water may exist due to it’s excellent lack of water permeability.

While TPO is available in multiple colors, it’s most common is white. A White TPO roof is a highly reflective and is a cool roof, exceeding current energy efficiency standards and is an US Department of Energy, Energy Star rated roofing system. TPO may qualify for tax credits and LEED points. TPO is truly a “green roof”.

TPO is commonly installed mechanically fastened or fully adhered. Due to its’ lightweight nature it can often times be installed over existing roofing systems (when code allows). TPO is available in thickness ranging from 45 mils up to 80 mills. As you can imagine the thicker TPO will be more durable, last longer, is able to be warranted for longer terms, but also does require more up front investment.

Single Ply – PVC Low Slope Roofing Options

Single ply PVC membrane is similar in appearance to TPO. However PVC has been on the market longer than TPO. The methods and manner in which a PVC membrane is installed is very similar to that of the TPO roof described above.

A PVC roofing system requires a slightly greater upfront investment than that of a TPO roof. However the roof installation is almost exactly the same. If you want the very best thermoplastic roofing system installed, with the peace of mind that comes with heat welded seams, choose a PVC roofing system. PVC is highly chemical resistant and has a longer proven track record.

Single Ply – EPDM Low Slope Roofing Options

EPDM is similar to TPO in the fact that it is a single ply membrane, however EPDM is a rubber compound instead of plastic, like TPO. EPDM has a strong reputation for durability. With properly taped seams and detailed flashings, an EPDM roof can easily last 30 years. However, unlike TPO, the seams are treated with adhesive making them vulnerable over the long term and may require maintenance sooner than a heat welded seam.

EPDM is commonly installed fully adhered or ballasted. However EPDM can also be installed mechanically attached. Ballasted EPDM roofs are very economical on large projects, when the structure can support the weight of the ballast material, typical washed river rock.

EPDM is available both reinforced with polyester scrim and non-reinforced in thicknesses ranging from 45 to 90 mills. 90 mill EPDM is the only EPDM membrane eligible for a 30 year system rating.

Definitions of Single Ply installation methods:

Fully adhered – a roofing membrane or a component of that system that is glued in place or otherwise secured with adhesives. Membranes may also be adhered using adhesives pre-applied at the factory. Fully Adhered roofs carry system ratings of 15-20 years (30 years on EPDM with proper design and construction of the roofing assembly).

Mechanically fastened – a roofing system or a component of that system that is secured in place using fasteners of some kind. Often these fasteners are button head nails or screws with plates. Regular shingle style roofing nails are not acceptable. Mechanically fastened roofs carry system ratings of 10-20 years.

Ballasted – a roofing system that is not fastened nor adhered in place. Instead the roof is weighted in place by the application of washed river rock, manufactured concrete pavers or other media of substantial weight. Ballasted single ply roofs carry system ratings of 10 years.
Mill Thickness can be translated into inches for better understanding. Since 1 mil = 0.001″ (or 1/1000 of an inch; hence it being called a “mil”), 45 mils = .045″. In fractions a 45 mill membrane would equal approximately 1/22″.

Modified Bitumen Low Slope Roofing Options

Modified bitumen is perhaps the most common of residential low slope roofing systems. However Modified bitumen has lost a tremendous amount of market share in Commercial and Industrial roofing projects.  Modified Bitumen is still often used in some Institutional (Schools and Government buildings) roofing projects.  Modified bitumen is installed in 3′ rolls, either torch applied using flame heat to weld the cap sheet to the base sheet(s) or self adhering using factory applied adhesives on the various components. Modifiued Bitumen can also be applied with cold process adhesives applied in the field.  The duration of your warranty term on modified bitumen is determined by the quantity and type of layers.

Quick specs for a typical modified bitumen roof assembly is as follows:

  • 1 layer felt or fiberglass base and 1 layer of smooth black modified bitumen – 10 year system rating.
  • 1 or 2 layers of felt or fiberglass base with 1 layer of smooth modified bitumen and an application of an approved reflective coating – 12 year system rating. (Please note that this reflective coating may require periodic maintenance or re-application to achieve a 12 year life cycle)
  • 2 layers of base with 1 layer of granulated modified bitumen – 15 year system rating.
  • 1 or 2 layers of felt or fiberglass base with a smooth modified bitumen mid-ply and a granulated modified bitumen cap sheet – 20 year system rating.
  • 1 layer of premium self adhering base with a granulated cap sheet – 20 year system rating.

People often wonder why their modified bitumen roofs last only 10 or 12 years and do not understand that is usually the system specification provided when hiring their contractor.

A note about modified bitumen in regards to city of Chicago energy and reflectivity codes; A smooth black modified and many granulated modified bitumen membranes will not meet current city of Chicago reflectivity requirements without the application of reflective coatings.

Selecting your Low Slope Roofing System Options

Choosing a roofing system for your property may be overwhelming if you don’t know the pro’s and con’s of each membrane. There are no one size fits all solutions. Each low slope roofing membrane may be superior for some conditions, while inferior for others. The determination of this longevity is how the new roof is designed and installed. For example a mechanically attached 45 mil single ply roofing system may be rated to last 15 years, while a fully adhered 60 mil roofing system with proper insulation may be rated to last 20 and 90 mil membrane may be warran ted up to 30 years.
Liquid Applied Roofing Systems (Coatings)

To learn more about liquid applied roofing systems please see also: Understanding Liquid Applied Roofing Systems. Liquid applied roofing systems are a wonderful alternative when removal of the existing roofing system isn’t necessary or won’t fit in the budget. Liquid applied roofing systems can be expected to last 5-15 years.


Post Author: Thomas Kral

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