Compiled this together to help some understand single-ply roofing aspects.
Questions and Answers;
questions:
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What are the advantages of thermoplastic membranes over thermoset?
What are the components of single-ply roofs? -
*What are the advantages of the newest single-ply membrane, TPO? *
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What are the differences between membrane attachment methods?
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What are single-ply roof membranes made of?
answers: -
Thermoplastic membranes are set in the field with exposure to the elements. The seams are welded with a heat gun, which makes them stronger than the sheet material. In thermoset membranes the seams are lapped and glued. This connection is often the weakest point in the system. Thermoplastic membranes are easily recycled, but thermoset membranes are not. Thermoplastics can be melted, purified, and re-extruded.
Single-ply roof membranes are flexible sheets of synthetic polymers. Membranes range from .033 to .060 mils thick, though they are available in heavier sheets. Most have a reinforcing sheet of polyester to prevent puncture, increase wind-load resistance, and improve dimensional stability. This layer is not necessary for some applications. There is a range of attachment methods, depending on the location of the roof and the type of membrane.
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Sheets of membrane are mechanically anchored, chemically adhered, or ballasted. With mechanical attachment methods, clips and metal plates, batten strips, or bars, are used. Fasteners secure the sheets at the seam edges. If there are not enough fasteners, the wind uplift can cause the fasteners to eventually work loose. A conservative fastening schedule is normally advised. Chemically adhered membranes use adhesives to hold the membranes to the roof substrate. The time and labor to apply the adhesive and smooth the sheets in place adds to the cost of the job, but the bond achieves a roof that is highly resistant to wind, water, and dimensional changes. Ballasted roofs weight the membrane with gravel or pavers. This is the least expensive application, but there are drawbacks. Wind can blow the ballast off causing damage to the membrane or other surfaces.
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TPO combines synthetic rubber with polymers, such as olefins, making a more stable formulation. This advantage, combined with the membrane’s low cost, makes it attractive. Disadvantages include a lack of testing and a limited number of installations, making it difficult to accurately assess the performance of the membranes.
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Roof membranes are made of several different chemical compounds. The oldest is chlorosulfonated polyethylene (CSPE), commonly known as Hypalon. The most widely used is ethylene propylene diene monomer (EPDM), commonly know as a rubber roof. Polyvinyl chloride (PVC) has been reformulated over the years to improve its durability and is available only as a reinforced sheet. The newest is thermoplastic polyolefin (TPO).
Hope this helps some.
Marcel 
