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Getting A Good Single-Ply Roof Design
February 22, 2017 - Contact FacilitiesNet Editorial Staff »
The first major factor is roof design. Pay attention to key considerations like these:
• Choose the correct color membrane for the building. A rule of thumb is to use a darker colored membrane when heating days exceed cooling days and a lighter one when the opposite is true.
• When the roof is over wide open spaces, choose a wider membrane. These require fewer seams than a narrower membrane. Since the most vulnerable part of a single-ply membrane is the seaming, less is generally better.
• Pick the insulation or direct membrane attachment method most suited to the deck type. Single plies are most commonly installed using screws and plates — sometimes over and sometimes under the membrane. Mechanical attachment — screws and plates — are better for wood, lightweight concrete, cementitious wood fiber, gypsum, and steel decks. In many cases, adhesives can also be used on these decks, depending on the roof to be installed. A concrete deck lends itself best to adhesives. Regardless of the attachment method, a deteriorated deck will cause problems, so it is mandatory to require the contractor to replace any areas of deck deteriorated to the point where a fastener will not properly hold, and areas that are damp to the point that the adhesive will not stick.
• Choose a system that fits the use of the building. A sturdier system that resists punctures is more appropriate for roofs subject to abuse, such as schools. A restaurant that spews greasy residue on the roof is not appropriate for a system that is deteriorated by hydrocarbon products. A membrane that is more resistant to deterioration from standing water is better for a place where the drainage is inadequate and not easily remedied by sloping insulation or adding new drains.
• The termination of the roof becomes even more important in a single-ply membrane system. Be sure that the metal termination method is appropriate for the wind conditions. Salt water exposure and high humidity make the corrosion-resistance of the edge metals of very high importance.
• Be sure the membrane is properly supported by a hard substrate, especially where hail or foot traffic is common. A soft substrate can allow the membrane to be more easily damaged as the soft substrate will depress and allow the hail to penetrate.
• If all else is equal, choose a membrane that is readily available in the area and that has contractors nearby who are qualified to install it.
• Together, the specifications and drawings form the contract documents that allow bidders to all bid on the same scope of work. More importantly, during the installation, the facility manager’s quality assurance inspector can use these documents to compare what is being installed with what the facility manager is paying for to be sure the roof is being installed according to the contract.
This quick read is from Karen L. Warseck, AIA, LEED AP, a registered architect and president of Building Diagnostics Associates. Click here for more from Warseck on keys to getting a good single ply roof. And click here for more on the roofing on Facilitiesnet.com.