Installing a PVC Roofing Membrane

While as a home or business owner, you will most likely not be installing a PVC roofing membrane yourself, it is important to have basic understanding of the installation process, so that you can ensure that your contractor is doing a good job.


As with any roofing material, ensuring that your PVC membrane is properly installed is a key determinant of the longevity and proper service of the roof. Many PVC roofing membranes that fail prematurely, do so because of initial incorrect installation done by an unprofessional roofer, rather than inherent flaws of the roof itself.


Prior to installing the PVC roofing membrane itself, typically some type of insulation board is put in. Most commonly used insulation is ISO or EPS foam board. Both of these insulation boards carry an R-value that ranges from 4-R to 6-R per 1 inch of insulation thickness. Insulation is important because it saves energy by reducing heat loss. Heat gain is taken care of by PVC’s cool white surface.


A PVC roofing membrane can be installed in three different ways. Regardless of what installation procedure is chosen, all PVC roofing systems are sealed with a hot-air welder. This ensures superior seam strength and makes the membrane resistant to leaks and wind blow-off. When choosing a time to install your PVC roof, note that the temperature of the heat welding of the seams is critical to getting a strong bond. Therefore, welder temperature should be adjusted upwards in the winter to account cooler ambient temperatures.


The hot-air welding of all seams and flashing is used on all PVC roof installations. Hot – air welding makes material overlaps last a lot longer, than those on EPDM rubber roofs and other torch applied or glued flat roof systems. The advantage of hot-air welding is that it can be done in the winter and does not require and adhesives to work, where as solvent based glue used in Rubber Roof installation will freeze, making installation or repair impossible.


In a nutshell, a PVC membrane is attached to the substrate using a special adhesive. Even though this is a quick and simple installation method, it has one major disadvantage. In case condensation forms underneath a PVC membrane, which sometimes happens as a result of poor ventilation of the roof deck, it will cause the adhesive holding the membrane in place to become loose. As a result, the loose membrane will be susceptible to wind blow-off. While the chance of such strong wind may be very small, the consequences of your roof being blown-off will be disastrous to your property and will cost thousands of dollars to repair. Thus, you need to evaluate whether you want to take even this minimal chance by choosing a full-adhered method of installation.

A fully – adhered method of installation is recommended in case your PVC membrane cannot be easily attached using screws or other types of fasteners, such as over a structural concrete deck. In this case, it is best to first attach the insulation with adhesive and then to attach the membrane to the insulation with adhesive  to minimize damage to the roof deck.

A fully-adhered membrane must always be mechanically along the perimeter, which greatly improves wind uplift.  Fully adhering your PVC roofing membrane will also eliminate the flutter that can occur in a mechanically – attached system.

NOTE – fully adhered installation method should only be used when the ambient temperature is above 40 F degrees, otherwise the adhesive will freeze, and membrane will not bond properly to the substrate, causing bubbles and delamination problems.


Another possibility is to mechanically attach your PVC roof to the substrate using heavy duty screws and barbed plates, which will hold the membrane down tight.  This type of installation ensures that even hurricane-level wind will not tear off your roof. If your building is located in a high-wind area, such as along the coast line or on a high hill, it is best to go for mechanically-attached installation.


In a ballasted installation, a PVC roofing membrane is laid across the substrate loosely, rather than being fastened or glued in place. The membrane is held in place with a ballast, which is typically made of washed river rock, manufactured concrete pavers, or other materials of substantial weight.