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Flat Roof Systems: What’s the Best Option?

man putting down roof tiles wearing gloves

There are several different low-slope roofing systems.  The type of system you currently have greatly affects what you can or can’t do to extend and get the maximum life out of it.

For many years, a built-up roof, or “BUR” was the gold standard.  Remember all the hot tar kettles you use to see everywhere? Even with all the roofing following Hurricane Irma, the smell of tar going down the road in a smoldering kettle is almost non-existent.  BUR systems may or may not have a layer of insulation and recovery board, depending on if there is insulation in the attic space or not. The roof starts with a layer of felt/fiberglass. This can be mechanically fastened or adhered with hot or cold-process tar.  Subsequent layers of felt are added and adhered by tar as you “build-up” the roof till you get to the specified layers. In non-high wind areas, rock ballast can be added. In high-wind areas a granulated cap-sheet is added, for better installations that cap-sheet is modified bitumen, sometimes called a rhino-hyde roof, in reference to the brand of cap-sheet and the expected longevity.

If you have a BUR, there are several options to extend its life, including a couple coating options, some of which have better warranties than your original roof had.  Small problem areas, such as blisters or bubbles, where the layers have delaminated, can be repaired and the full roof coated. Some of these systems have 10-year renewable warranties!  For 20-30% of the cost of replacing a roof, you can continue to repair and recoat it and extend the warranty another 10 years!

If the roof went through a hurricane or other wind event, it can be damaged to the point that it’s no longer repairable.

EDPM or Rubber roofs are far less common than they use to be.  They are single-ply thermoset membranes. They can either be fully adhered or perimeter adhered.  One of the least expensive roofing options is a perimeter adhered EDPM roof, but it is not a good system.  The tension created as the rubber heats and contracts is just too great. Whether the edging pulls loose or the membrane itself tears, there are far too many problems to be a practical solution for occupied living space.  Fully adhering (gluing) the membrane to the roof deck alleviates the extreme tensions, but it doesn’t make it a perfect system.

Again, with EDPM there are repair and coating options available.

Single-ply thermoplastic membrane systems (PVC or TPO).  While PVC and TPO are different products, their use and application are very similar.  Preformed sheets with hidden fasteners and heat-seamed seams provide a durable roof with relatively few problems.  Both come in extremely reflective white for maximum energy savings, and they can come in other colors where visual appearance is more important than practical usage.

In general, for single-ply systems TPO and PVC are smooth, chemically resistant and water-resistant, and neither is easy to coat. For PVC membranes, high levels of liquid plasticizer seem to present a bigger challenge than their slick surfaces. The chemical resistance of these polymers also inhibits the development of suitable primers, and these systems do require special primers for coating. This is not a common application and is an area of ongoing research.

Note that TPO and PVC membranes are easy to misidentify in the field. Because they require different primers and coatings, examining a test patch is a prudent precaution before coating an unidentified white membrane.

FOAM (SPF).  This is a polyurethane product that has many applications including going over existing roof systems.  There are some great advantages in that thickness can be varied to create slopes. The product provides additional insulation, and with the proper coatings, is certified for high-wind use and is very resistant to hail damage as well.

If you are considering replacing, coating, or just looking for a proposed maintenance schedule you can contact us to get a non-biased opinion.  We do not sell roofs, maintain roofs, or even repair roofs. We maintain our neutral position to maintain our ability to provide you and unbiased opinion.

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