SpecTopics: Mechanically Attached vs. Fully Adhered Roof Systems
When selecting a roof system, architects and specifiers are often faced with the choice of specifying a mechanically attached or an adhered roof. This is an important decision as it can affect the project’s cost and timeline, the roof’s performance, and the overall installation process.
Mechanically fastened systems, where the membrane is attached using fasteners and plates or battens in the seams, have historically been popular with when using reinforced EPDM or thermoplastic membranes such as TPO and PVC. Non-reinforced EPDM membranes have typically been fully adhered with solvent- or water-based contact adhesives. With the advent of new adhesives and installation technology, the share of TPO and PVC roofs that are adhered is also growing.
Mechanically attached roof systems are often viewed as a cost-effective option with few installation temperature restrictions. This is often true; however, it is also important to consider the benefits that a fully adhered system can bring, especially when faced with the option to “value engineer” an adhered spec to a mechanically attached installation.
Performance: In a fully adhered roof system, adhesive evenly distributes the uplift pressure on the roof membrane and substrate, rather than focusing it on fastening points in the seams. This is why fully adhered systems typically have superior wind uplift results and code approvals vs. mechanically attached systems, providing the best long-term performance.
Seams: Adhering a membrane allows the installer to use the widest possible sheet to reduce the number of splices in the roof. In mechanically fastened systems, sheet width is dictated by fastener spacing and typically narrow-width sheets are required around the perimeter of the building to resist wind uplift. This results in more membrane seams and more fastening points throughout the roof deck.
Aesthetics and Sheet Flutter: Fully adhered systems provide a “tight” looking roof because the membrane is fully bonded to the substrate beneath it. In mechanically attached systems, the membrane is only fastened in seam areas, allowing the rest of the sheet to flutter in the wind. This can give the roof a loose appearance and create noise below the deck on very windy days.
It is also worth noting that several innovations have reduced some of the limiting factors of installing a fully adhered roof:
Temperature Restrictions: In the past, many bonding adhesives would not allow installation of an adhered roof below 40°F (4°C) and rising. New adhesives such as CAV-GRIP® III and CAV-GRIP PVC have now made it possible to install fully adhered roofs in temperatures as low as 25°F (-4°C). In addition, exclusive RapidLock™ technology uses a hook-and-loop fastening system that eliminates temperature restrictions.
Odors and VOC Restrictions: Fumes and odors from adhesives can be a challenge when roofing occupied buildings; however, CAV-GRIP III and CAV-GRIP III PVC are not only Low-VOC, but also low-odor compared to traditional solvent-based bonding adhesives. While mechanically attached systems virtually eliminate the need for adhesives and the smells they produce, Self-Adhered Technology™ (SAT), RapidLock technology, and VacuSeal technology can provide the performance of a fully adhered system while virtually eliminating the need for adhesives.
For further information on various membranes and systems, consult the Carlisle Systems Brochure.
Contact Craig Tyler with questions.
Mechanically fastened systems, where the membrane is attached using fasteners and plates or battens in the seams, have historically been popular with when using reinforced EPDM or thermoplastic membranes such as TPO and PVC. Non-reinforced EPDM membranes have typically been fully adhered with solvent- or water-based contact adhesives. With the advent of new adhesives and installation technology, the share of TPO and PVC roofs that are adhered is also growing.
Mechanically attached roof systems are often viewed as a cost-effective option with few installation temperature restrictions. This is often true; however, it is also important to consider the benefits that a fully adhered system can bring, especially when faced with the option to “value engineer” an adhered spec to a mechanically attached installation.
Performance: In a fully adhered roof system, adhesive evenly distributes the uplift pressure on the roof membrane and substrate, rather than focusing it on fastening points in the seams. This is why fully adhered systems typically have superior wind uplift results and code approvals vs. mechanically attached systems, providing the best long-term performance.
Seams: Adhering a membrane allows the installer to use the widest possible sheet to reduce the number of splices in the roof. In mechanically fastened systems, sheet width is dictated by fastener spacing and typically narrow-width sheets are required around the perimeter of the building to resist wind uplift. This results in more membrane seams and more fastening points throughout the roof deck.
Aesthetics and Sheet Flutter: Fully adhered systems provide a “tight” looking roof because the membrane is fully bonded to the substrate beneath it. In mechanically attached systems, the membrane is only fastened in seam areas, allowing the rest of the sheet to flutter in the wind. This can give the roof a loose appearance and create noise below the deck on very windy days.
It is also worth noting that several innovations have reduced some of the limiting factors of installing a fully adhered roof:
Temperature Restrictions: In the past, many bonding adhesives would not allow installation of an adhered roof below 40°F (4°C) and rising. New adhesives such as CAV-GRIP® III and CAV-GRIP PVC have now made it possible to install fully adhered roofs in temperatures as low as 25°F (-4°C). In addition, exclusive RapidLock™ technology uses a hook-and-loop fastening system that eliminates temperature restrictions.
Odors and VOC Restrictions: Fumes and odors from adhesives can be a challenge when roofing occupied buildings; however, CAV-GRIP III and CAV-GRIP III PVC are not only Low-VOC, but also low-odor compared to traditional solvent-based bonding adhesives. While mechanically attached systems virtually eliminate the need for adhesives and the smells they produce, Self-Adhered Technology™ (SAT), RapidLock technology, and VacuSeal technology can provide the performance of a fully adhered system while virtually eliminating the need for adhesives.
For further information on various membranes and systems, consult the Carlisle Systems Brochure.
Contact Craig Tyler with questions.
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