PVC & TPO Roofing Systems
TPO & PVC Single Ply
Thermoplastic Single Ply Roofing has been growing rapidly in popularity and market share over the past decade as it provides an excellent lightweight system that is in tune with the push towards "green buildings". Thermoplastic single-ply roofs are either “PVC” or “TPO”, and are known as Cool (White) roofs due to their unique energy efficient design.
Also, being a true “single-ply” system, these roofing systems can cost substantially less than any type of conventional built-up system.
TPO and PVC are “Cool Roofs”
To understand the concept of a cool roof, there are two factors that need to be explained; reflectivity and emissivity. Reflectivity describes the amount of solar energy that is reflected back by the roofing membrane into the sky. A white membrane would reflect the most while a dark membrane would reflect much less. Emissivity is basically a measure of how well the membrane can shed heat. For example, a white surface will repel the most heat while a black surface will absorb the most.
The higher the emissivity and the higher the reflectivity of the membrane, the more energy efficient the design. Thermoplastic roofs have the highest reflectivity and emissivity values, explaining why they have increased in market share so substantially in recent years and are becoming great alternatives for Chicago buildings. Read more about Johns Manville Cool Roof Solutions.
Single Ply Roofing Installation / Application
There are two methods to install a thermoplastic single ply membrane: mechanically fastened or fully adhered.
Mechanically Fastened TPO / PVC
In a mechanically fastened approach, the TPO or PVC membrane is laid out in shingle fashion according to the existing drainage pattern and roof deck flutes orientation. The field membrane is then fastened through the new insulation layer in the leading edge of the sheet with specific fasteners and plates at 12” O.C. The following sheet is then lapped over the screwed edge of the previous sheet with a consistent minimum 6” lap and the 1.5” seam is then heat welded using the robot. The perimeter of the roof is “picture-framed” to increase the fastening pattern for Factory Mutual wind uplift approval. The details, flashings, and other welds that cannot be performed by the robot are then performed by hand using handheld hot-air welders and seam rollers. This has become the most common application for TPO roofing systems due to its extremely economical and cost-efficient design.
Fully adhered single ply roofing systems are installed in the same fashion as a mechanically fastened system in terms of how the rolls are laid out, how the insulation substrate is attached, and in which direction the laps of the sheet face. Fully Adhered TPO Single Ply Roofing Systems. The difference in fully adhered single ply roofing systems is that the sheets themselves are never mechanically attached to the roof deck and are instead bonded using special adhesives directly to the insulation substrate layer. The membrane adhesive is applied both to the top surface of the insulation layer and the bottom surface of the membrane at specified coverage rates using a combination of rollers and spreaders. Fully adhered specifications are Factory Mutual approved (I-60 for Chicago) and provide a “tight” look and feel that a mechanically fastened system may not be able to achieve due to its inherit design. These systems do have a specific timeframe in which they can be effectively applied in response to the requirements of temperature for the bonding adhesives. If you are interested in installing a fully-adhered single ply roofing system on your building, plan to have the project completed by mid October at the very latest.
Dimensional Stability / Shrinkage Factor
There are several dramatic differences between TPO/PVC and EPDM, the most important of which is what’s known as “dimensional stability” or shrinkage factor. EPDM (rubber) is well documented for its relatively high shrinkage factor (3-5%), which can prove to be problematic around roof penetrations, perimeters, units, etc. because the membrane will commonly shrink to the point that “tenting” may occur around these items. This stress can cause splits, tears, and other issues. Thermoplastics on the other hand, TPO and PVC, are extremely dimensionally stable with a shrinkage factor of under .01%. The stability is due not only to the chemicals involved in the sheet but also a reinforcing element (polyester for TPO, Elvaloy KEE for PVC) that helps to limit expansion/contraction.
In a thermoplastic system, the seams are all welded with hot-air. Field seams are performed using a “robot” that fuses a consistent 1.5” weld while details (flashings) are done by hand with handheld hot-air welders and seam rollers. Due to the permanent nature of this type of seam, major manufacturers will commonly allow the finished roof to have small ponding areas and still be eligible for a strong guarantee.
TPO and PVC are commonly white membranes although they are also available in a wide array of other colors as well. This provides for excellent surface reflectivity and emissivity properties.
A thermoplastic single-ply roofing system from Roofing Solutions can be eligible for a full system guarantee from the manufacturer for up to 30 years. This guarantee is a No-Dollar-Limit warranty, meaning that it is worth the same amount on day 1 as it is on day 7,300 without pro-ration of any kind. As a Johns Manville Peak Advantage approved contractor and Firestone Red Shield approved contractor, Roofing Solutions can provide you with the ultimate in peace-of-mind from a guarantee standpoint alongside first-class workmanship.
TPO Roofing Specifics | Thermoplastic Polyolefin Roofing Systems
TPO roofing is quickly becoming a prominent staple of new construction for all of the big box retailers and warehouses you see throughout the country. Much of the industry has shifted to the thermoplastics over other alternatives due to several of the aspects mentioned above. This material also makes for a great approach to retrofit/recovery systems because it is very lightweight and when installed in strict accordance with manufacturer specifications, can carry a complete 20 year workmanship and material guarantee the strongest warranty available in commercial roofing. This material is the lower cost alternative of the thermoplastic single-ply’s when compared to PVC. TPO roofing systems offer a fire-resistant membrane that is essentially comprised of two plies of thermoplastic that are laminated together with a polyester reinforcement to strengthen the bond. The membrane is also resistant to chemical and grease. Other traits of TPO roofing systems include a more puncture resistant and durable surface than EPDM, allowing for more rooftop traffic. TPO roofing systems can also easily repaired using TPO patches, certain coatings, and repair tapes.
PVC Roofing Specifics | Thermoplastic Polyvinyl Chloride Roofing Systems
A PVC roofing system is arguably the best system available in the realm of single ply roofing systems. PVC membranes are manufactured using UV-resistant polyvinyl chloride and Elvaloy KEE (ketone ethylene ester) formulation. The Elvaloy KEE formulation allows for added long-term flexibility of the membrane. In addition, Johns Manville PVC membranes are reinforced with a non-wicking polyester fabric and Aramid fiber-reinforced edge-making the construction of this sheet the most durable of all single-ply’s in terms of puncture and tear resistance.
PVC roofing systems, as mentioned above, can be installed in the same fashion as TPO systems: mechanically fastened or fully adhered. PVC roofing systems are also fire-resistant and resistant to chemicals and grease. Similar to TPO, PVC roofing systems also feature an element of easy maintenance and repairs.
For more information regarding Single Ply Roofing, please visit the following links:
- National Roofing Contractors Assoc. (NRCA) - Thermoplastic Membranes
- Johns Manville Single Ply Roofing Systems