Helene Hardy Pierce, FRCI, Vice President of Technical Services, Codes, and Industry Relations, GAF
Asphalt shingles dominate the steep slope roofing market and have proven their durability as a product choice that can perform for a very long time. Key to their performance is a good installation which is easy when roofing contractors follow installation recommendations provided by the manufacturer. Often when there is a performance issue, it is simply that one or more basic “rules” were not followed.
Review of over 10,000 punch lists from roof inspections on asphalt shingle roofs found that almost all deficiencies identified could be avoided by just following a few key roofing principles. Certainly, the cost of failure for roofing contractors in terms of reputation, cost of call backs, loss of future business, etc. can be high – so paying attention before you pull off of a shingle roofing project can avoid a lot of hassles and help contribute to your bottom line.
Where were these common problems found? There were eight distinct areas: product selection, missing components, ventilation, drip edges, chimneys, penetrations and flashings, valleys, and fasteners. While this might seem like a long list, when taken as a whole, consider that simply checking eight areas for common errors can help you ensure that your property owner is going to have a roof that should perform for a very long time.
Simply put, the right product needs to be used on the right slope. Traditionally, asphalt shingles have been considered “steep slope” products and perform well on slopes 4:12 or greater. They also can perform on lower slopes, some down to 2:12 when installed with special steps, such as a double layer of underlayment. But if they can’t use gravity and slope to shed water, they won’t keep water out of the roof. So, a good rule of thumb is that if the roof slope is less than 2:12, or higher for some shingle styles, the roof will
leak – shingles shed water, they are not waterproof.
In Florida, ice and water dam protection materials are not critical like they are further north, but beyond cold climates, these materials provide extra protection at penetrations, in valleys and along eave and rake edges. Another component that is critical but sometimes not found is the starter course at the eave edge. This course is very crucial for the wind performance of the roof since it seals the first course of shingles and prevents their tabs from lifting.
Improper, unbalanced, or inadequate ventilation can result in condensation problems that, at the least, cause ghost leaks and more seriously, cause mold, rot, and deck deterioration. In humid climates like Florida, proper ventilation of both heat and interior generated moisture is important to the long-term performance of the roofing system. Another ventilation problem is improperly fastened ridge vents – using the wrong (typically too short) fastener can result in leaks and blow offs of this critical component of the roofing system.
Metal drip edges direct water off of the roof and prevent wicking of water under the shingles at the edge of the roof. They also keep water from running down fascia and getting behind soffits and walls. If the drip edge is left out, it can result in deterioration of the deck, fascia, and soffit and also allow water infiltration into the building.
Chimneys on roofs have two common installation problems – missing step flashing and missing crickets. Step flashing diverts water away from the chimney/roof interface and provides long term performance at the deck/chimney wall joint when installed properly with the shingles that butt up against the chimney wall. Crickets on the “upside” of a chimney move water from what is often otherwise a no-slope valley and prevents water as well as debris from sitting behind the chimney and causing premature aging of the roofing materials. They also direct water down the roof and can prevent water from being forced over base flashings in a heavy downpour of rain.
Most steep slope roofs have penetrations that interrupt the shingles installed in the field of the roof, such as vents and pipes, and there are proper details that allow them to be flashed into the field of the roof and not allow water into the interior. Unfortunately, there are also penetrations where another trade has decided to use the roof as a platform to “hold” something on the roof, such as satellite dishes, lighting fixtures, signs, wires, etc. and often these additions are simply fastened to the deck through the roof. This results in holes that will eventually leak and let water through the roof deck. Penetrations that roofing contractors flash should simply shed water like the shingles that surround them and should not have fasteners that are not covered by a shingle course.
Another common flashing error is missing step flashing at walls. Like on the chimney wall, step flashing diverts water away from the wall and provides long term performance when properly “stepped” into the installed shingles. It also provides a detail that allows the roofing system to be joined with dissimilar materials that are used on the wall. Caulk/sealant is not a long-term solution, especially where a vertical surface meets a sloped deck.
Valleys are probably the most difficult part of any shingle installation. Understanding that a few steps ultimately determine whether the valley will perform or not can help roofing contractors avoid long term problems. When installing open or closed cut valleys, clipped corners of the shingle direct water down the valley and not under the shingles and then sealing the shingles in the valley reduces the chance that water will travel under the shingles in the valley, especially in a heavy rain. Likewise, using a woven valley with a laminated or many of the specialty shingles available today can result in bridging in the valley, wind damage, and poor resistance to water entry from wind driven rain.
It is really simple: fasteners keep the shingles on the roof. Nail pops, underdriven fasteners, overdriven fasteners, exposed fasteners, and high nailing can each cause their own type of problem. Nail pops and underdriven fasteners keep the shingles from sealing and often times cause a distortion that is visible from the ground. Eventually over time, they can actually break through the shingle that is laid over the fastener.
Overdriven fasteners have little holding power and often are associated with the use of pneumatic nail guns. Exposed fasteners create “shiners” on the face of the roof and eventually will leak; high nailing can result in wind damage prior to shingles sealing. In addition to these installation errors with the fasteners themselves, not using enough fasteners, particularly in high wind areas where additional fasteners may be required can cause problems in the future.
Checking these few areas to ensure a good installation is a great way to avoid problems. A few other key items to not forget include: avoiding patterning by following the manufacturer’s instructions for starting each course; making sure there is a minimal overhang at the eave edge to work with the drip edge and move water off the roof; being aware that mansards (very steep roofs) typically will require extra installation attention, making sure that hip and ridge shingles are installed correctly to finish off the top of the roof; and verifying that the fasteners being used are either all the way through a plywood deck or at least ¾” into a wood deck.
Today, a wide product offering of asphalt shingles is available for homeowners and contractors. Some of the most popular designs remain wood-shake style and slate-style shingles, but many manufacturers have also created unique new shapes to match a particular architectural style. These many choices and colors provide great aesthetics and options to compliment any home. When combined with a professional installation, asphalt shingle roofs can last a very long time.
Helene Hardy Pierce is Vice President of Technical Services, Codes, and Industry Relations with GAF in Parsippany, NJ.
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