Building a PV array to face diverse site factors such as wind, moisture and hurricanes can be very challenging. Roof Tech’s experience of deploying PV arrays in Japan is now having an influence in the U.S.
Each PV module is secured with multiple fasteners to spread the mechanical load evenly over the roof surface, as well as to alleviate torsion applied to a roofing system from thermal stresses. The thermal contraction and expansion of an aluminum array with a high coefficient of thermal expansion has the most movement on top of a roof. Roof Tech’s design, with the rail as the module frame, has mitigated effects to the degree that the distance between adjacent rows can be as low as 3mm (1/8”). Notice that mid and end clamps are 4” wide. This is for the purpose of distributing the clamping pressure on a larger surface of the PV panel frame.
The next step is the sealing of each attachment point with RT Butyl tape. Butyl was first developed in the early 1930’s and is the most important material today for the inner linings of tubeless tires. Among its traditional applications are pool linings and flexible flashing for construction.
Butyl rubber’s unique combination of barrier properties, high damping, resistance to ozone, weatherproofing and heat aging make it the ideal choice for many construction applications. For instance, butyl rubber is commonly added to asphalt compositions in roofing material manufacturing to improve the weatherproofing and low-temperature properties of the asphalt.
Roof Tech’s RT Butyl tape is easy to mold 
yet highly resistant to punctures. Butyl tape retains its elasticity and strength when exposed to service temperatures between -40° F and 248° F. Even with extreme fluctuations in temperature, butyl tape allows for expansion and contraction while preventing moisture from passing through. It has an effective life of 20+ years and is resistant to aging weather, mildew, acids, alkalis and salts. No matter how the attachment of a
PV array is achieved, the ultimate sealing point is at the penetration in the roofing paper, where a lag or fastener gets attached to the frame or roof sheathing and this is conventionally accomplished with the use of sealants. If you pick up a sealant and check the upper service temperature for the product, you may find a maximum of 200° F. RT Butyl performs at higher temperatures (248° F), which indicates greater endurance from heat distress.
At Roof Tech’s parent-company Yanegiken, a product is not released to the market before diligent testing. Complete roofing sets were tested under constant UV light, 145.4° F temperature, 50% humidity and a frequent water spray inside the Carbon Arc machine. The specimens were monitored and at 7,500 hours (almost 1 year later), the specimens were evaluated. RT Butyl tape was still flexible and performing its job.
Photo: Hurricane simulation at Yanegiken Laboratory, Japan.
As far as metal flashing concerns, the code is simple: roof-mounted PV system flashings must be installed in a manner that prevents moisture from entering penetration through the roof plane (IBC & IRC 2012). The current suggested guideline by the NRCA (National Roofing Contractor Association) for the installation of a PV system on a steep slope asphalt shingle roof shows the metal flange to be applied underneath the roofing paper (upper underlayment) for the proper water shedding. However, such step can only be accomplished along with the installation of a new roofing system; it is the proper way to produce a water shedding flashing mechanism. This can’t be done on a retrofit installed above an existing roof, which is the case for a majority of installations in the U.S.
The array installation would normally take 2 hours with a rail based system. Once the installer got to understand the process, the time for similar array assemblies dropped to 40 minutes. (Photo courtesy Border Solar)
The roofing paper is commonly called a secondary layer to protect the roof decking. I, on the other hand, refer to it as the first layer, because it’s the first one to be applied, and if the roofing material (or anything else) fails, the roofing paper is the layer that will protect the decking from moisture intrusion. With this in mind, the removal of nails to allow for proper placement of metal flashing actually creates a hole in the roofing paper, an entry point for moisture. The Center for Environmental Innovation in Roofing does not recommend water shedding flashings on the roof where there is potential ice damming, such as eaves or overhangs. It is recommended to use waterproof flashings in areas where ice damming may occur.
The separation of shingles can be treated as a failure to seal the roof, drastically reducing the warranty from the roofing manufacturer. For instance, a GAF roofing product had its warranty reduced from 50 years to 15 for a failure to seal correctly. A roofing manufacturer will want to be more involved in recommending PV systems that will be installed on its rooftop.
A recent installation in Southern Texas by Border Solar where RT-[E] Mount is placed on a Tile Roof (asphalt roofing system installed underneath the array). It’s a great looking array and the extra cost of the asphalt roofing installation can be offset by the additional installation time when installing PV arrays on top of tile roofs.
Roof Tech is founded on 40 years of experience in the roofing industry with over 400,000 PV residences in Japan, all sealed with the same butyl tape. RT-[E] Mount is a fully waterproof PV mounting system that is tested, certified and code compliant.
Based on extensive testing for water resistance and durability, the ICC Evaluation Report is available online. Professional Engineering (PE) reports for the attachment to the roof decking (OSB 7/16”, Plywood 15/32”), as well as for rafter installations are also readily available on the support page at roof-tech.us/support/.
By: Milton Nogueira, Senior Business Development Manager at Roof Tech
Roof Tech
www.roof-tech.us/
