Most asphalt shingle roofs built in the United States are built in virtually the same way from contractor to contractor. In many cases, these roofs are built to industry standards. But can we do better? Industry standards from organizations like ASTM, the Asphalt Roofing Manufacturers Association (ARMA) and various roofing shingle manufacturers are basic and minimum standards.
In this article I will demonstrate that a better Asphalt Shingle Roof System can be built and this is accomplished by installing better details that exceeded industry standards primarily at penetrations through the roof and intersections in the roof. These details are the cause of most residential roofing leaks and can be avoided at a small additional cost,
Roof Penetrations
A roof penetration is anywhere a pipe or vent penetrates through the roofing system. If not properly flashed, these penetrations can be the cause of many homeowner headaches. The plumbing system in your home requires venting to allow sewer gas to escape through the roof, preventing odors from building up in the home. These vents are pipes that penetrate the roofing system, usually PVC pipe. These penetrations must be properly flashed to prevent rainfall draining off the roof from entering the home.
Additionally, cooking odors and bathroom odors are also vented through the roof through sheet metal ducts that exit through louvered sheet metal vents in the roof. Homes with gas central heat and or gas water heaters also need to be vented via metal ductwork that exits through vents called roof jacks the roof.
The minimum flashing practice is sealing the new shingles to the vent flanges with asphalt cement and most contractors stop there. My team and I take additional steps to provide multiple layers of protection at these penetration locations in your roof.
First of all, every penetration detail starts with a gasket of ice and water shield self-adhering membrane two inches larger than the vent flange perimeter and is cut to seal tightly around the penetration and then sealant is applied where the penetration meets the gasket. The exception to this sealant step is at pipes that vent hot air exhaust. Then the vent flashing is installed, and asphalt roof cement is applied to seal the new shingles to the vent flange.
Finally, in addition to the rubber seal in the metal flashing that seals the pipe to the flange we apply an additional rubber rain collar for a third layer of protection. This final step may be the most important one of all. The rubber seal in the metal flange of the pipe flashing will begin to fail with time due to Ultra Violet Degradation (usually eight to twelve years). This additional rain collar acts as a sacrificial shield keeping the UV rays off the primary seal.
Valleys
Valleys are one the most critical flashing locations in a residential roof. Valleys are intersections where the water run-off from multiple roofs comes together before existing the roof. A leak here can be disastrous because of the high volume of water congregating in these areas that enter the home through voids caused by faulty workmanship or damage. Most contractors either line their valleys with sheet metal or ice and water shield self-adhering membrane.. My team and I do both. First, we apply 20” wide sheet metal valley liner then we overly the sheet metal valley liner with a 40” wide ice and water shield self-adhering membrane. The reasoning behind these extra steps are based on experience.
I have observed that when sheet metal valley liners are used, sometimes the roofing nails used to secure the liner are placed too low in the valley and missed with the asphalt roof cement causing leakage. To address the problem the industry has endorsed the use of ice and water shield self-adhering membrane as a valley liner instead of metal valley liners because they are self-adhering and require no nails for attachment.
Additionally due to the self-sealing modified bitumen properties found in ice and water shield, nails used to fasten the shingles in place can be driven through it without causing leaks. So then, why do both?
I have also seen foot traffic, sharp and or heavy objects damage the ice and water shield self-adhering membrane before the roof is completed and missed by the shingle installer resulting in future roof leaks. With metal valley liner installed first it is much less likely to have anything penetrate the ice and water shield self-adhering membrane and that’s why we do both.
Please look for my next article on Building The Best Asphalt Shingle Roof: Part Two – The Rest of the Story for more important information on Building The Best Asphalt Shingle Roof!
