What are Asphalt Roof Shingles?
Asphalt roof shingles are the most common covering found while inspecting roofs in Florida. Early shingles were made by saturating rag-felts with asphalt and by coating each side of the saturated felt with an asphalt-mineral filler-coat, covering the top surface of the shingle with mineral granules (sunlight and weather resistance) and coating the bottom surface with a material to prevent shingles from sticking together in storage or shipment. Beginning in the 1940’s the felt mat was changed to a zero rag-content using wood fibers and cellulose (newspaper). More recently many manufacturers began producing shingles using a fiberglass mat to replace the felt. The fiberglass mat was thought to have good tear resistance, possibly slightly better fire resistance, and as the mat was generally thinner than the felt mat, we believe that there were also economic advantages for both the manufacturer (less asphalt used in the mat) and the roofing installer (lighter material, easier to install).
Ten Reasons Roofs Fail
1. Blisters. Bubble-like or long, thin raised areas on the roof are called blisters. Blisters are the most common roofing problem. They occur when a gas, usually water vapor, is trapped within the roofing system either between the plies or between the plies and the insulation. The heat of the sun during the day causes the gas to expand. The expansion of the gas creates a pressure within the system that pushes the plies apart, resulting in the blister.
Blisters would not occur if there were not some reason for moisture in the membrane. Two common ones are applying the roof to a damp substrate, as during a re-cover, and applying wet materials, such as felts, that have absorbed dew or rain on the edges. The moisture that causes blisters can often be traced back to another problem: improper storage of insulation, which allows water to soak through holes in shrink wrap or at the bottom of the stack where shrink wrap doesn’t cover. Moisture can also get into a roof installed in the presence of rain, snow or dew.
2. Open laps. Open laps in the field membrane, but especially in the flashings, are another problem. Open laps are just carelessness on the part of the installer. Usually it means that the installer has failed to apply adhesive to the entire lap. Sometimes it is caused in built-up and modified-bitumen systems when the bitumen is applied too cold. The laps appear to be closed, but open up as the roof ages.
In single-ply membranes, open laps are usually caused by improper surface preparation, such as adhering to a dirty membrane, heat welding at too cold of a temperature, not allowing the adhesive to dry properly or applying too much or too little adhesive.
3. Splitting. The most common splits occur when a metal accessory is flashed with a membrane material. As the temperature changes, metals and membranes expand and contract at very different rates. Because the membrane generally cannot move as much as the metal, it will eventually fatigue and crack when it is adhered to metal. This problem is not as common with single-ply membranes with better expansion and contraction capabilities, but it is common in asphalt and coal tar systems.
Splits occur frequently in expansion joints. Contractors rarely know how to properly terminate an expansion joint cover. They run it to the wall and stop it dead. Unfortunately, the movement in the building does not stop at the end of the expansion joint and, consequently, it rips open any attempt to seal that edge. Splits are also common at joints within the expansion joint cover itself.
Splits are not limited to flashings, however. As most roofs age, they become more brittle and less resilient. This means that they become less resistant to movement from common sources such as temperature changes, foot traffic and substrate movement. Because the roof cannot flex or stretch as well as it did when new, it cracks.
Probable Cause:
It’s possible that shingles made by some manufacturers do not meet the ASTM Standards for tear resistance.
Even where shingles meet the Standards, it’s possible that the standards themselves were defective.
In any case, Fiberglass mat may lack adequate tear resistance.
Self-sealing tabs on shingle backs may glue shingles together with too much strength, causing the roof covering to form a single large membrane which cannot accommodate large temperature changes.
Reduced total amount of asphalt in thin fiberglass mats might become brittle after exposure to heat and sunlight.
Temperature swings probably contribute to the onset and extent of tearing, and we’d expect worse tearing where temperature swings are more extreme such as in Northern climates.
Nailing or placement pattern of shingles: “laddering” vs. “staggered.” On laminate and strip type shingles we have inspected roofs on which damage is found occurring at the corners of shingles rather than in the middle of the shingle material. It appears that as temperatures dropped and the glued-together-roof-membrane cools and contracts, the natural point at which movement occurs is where shingles are end-butted together. When the pattern of end-butts is laddered rather than staggered up the roof we have found corners tearing off of shingles following the laddering pattern exactly. (Laddering is not a recommended installation pattern according to NRCA and ARMA publications nor according to instructions from some manufacturers.) Laddering alone cannot be blamed for this failure however, as we have seen similar shingle tearing following a staggered end-butt pattern up other roofs. However laddering may indeed create a more localized natural point of separation on a roof, causing most of the movement to occur in a smaller area when the roof material contracts with cooling.
4. Punctures. The most preventable failure symptom, punctures usually occur because of carelessness on the part of people visiting the roof: HVAC technicians, window washers, painters, maintenance staff, smokers and tenants. Punctures can also occur because of debris left, blown or tossed on the roof. They may appear as tears or holes.
5. Penetrations. Another common failure location is penetrations. Of particular concern are pitch pans. There are three failures common to pitch pans: the sealer itself, the container in which it sits and the penetration to which the sealant is supposed to adhere. Almost all sealers used in pitch pans will crack eventually due to loss of plasticizer or aging. If the penetration is not stabilized, vibration or movement of the penetration can cause the sealant to crack around the penetration. If a penetration is not thoroughly cleaned of asphalt before installing pourable sealers, the sealer will not adhere to the penetration.
Other types of penetration flashings also can fail. Concrete curbs filled with sealer will crack if not fully supported underneath. Metal pans eventually rust and lose adhesion to the sealer. Rubber and plastic boots will deteriorate with ultraviolet radiation exposure. The sealant used at metal penetration flashings eventually deteriorates with exposure and may not seal to the penetration if the penetration has not been properly cleaned before installation. The penetration flashing may also leak if the wrong diameter flashing is used or the cover is not correctly installed.
6. Wrinkles. Wrinkles can occur both in the flashings and within the membrane itself. When there is differential movement between the roof deck and the perimeter, the flashings will wrinkle on a 45-degree angle. When a wrinkle reaches the edge of a membrane or flashing, the opening left at the end of the wrinkle is called a fishmouth because of its bass-mouth-like appearance. Depending on the ply in which the wrinkle occurred, the fishmouth can be a tunnel for water to get down into the building.
Wrinkles within the membrane will eventually fatigue and crack. Because they are raised above the surface of the roof, they are more prone to traffic damage, scuffing and surfacing loss than the rest of the roof.
7. Flashings. Flashings must be fastened at the top to prevent the membrane from slipping down the wall or curb, or to keep the membrane from creating a funnel into the building. A flashing normally terminates under a metal counter flashing. If it does, the counter flashing can create problems if the top is not properly sealed or the sealant has failed. If the metal counter flashing does not lap the membrane enough, it may fail to divert water from the flashing and instead funnel water into it.
8. Surfacings. Surfacings on membranes may provide protection from ultraviolet radiation and damage from traffic on the roof. They also may be a component of the fire rating of the roof. In the case of ballasted roofs, surfacings may be the only thing keeping the roof in place other than gravity. When the surfacing gets displaced or worn off, either from foot traffic, repair persons, wind, etc., this protection no longer applies.
9. Fasteners. In mechanically attached roofing systems, movement from wind will cause fasteners to rock back and forth with the gusts. Eventually, this movement causes the hole in the deck around the fastener to enlarge and the fastener to back out. The fastener heads can eventually puncture the membrane from below. But fastener back-out is not limited to single-ply membranes. It is also a common occurrence in metal roofing and in metal accessories on membrane roofs. In these cases, the backed-out fasteners leave holes where water can directly enter the building. This is an especially serious problem when a coping — the metal cap on the top of a parapet — is fastened through the top of the horizontal portion and not through the vertical flanges.
10. Abuse and Neglect. When it comes to mistreating a roof, the most common culprits are air conditioning and maintenance technicians, window washers, and sign installers. It is not unusual to see debris — ranging from screws and bits of sheet metal all the way up to empty refrigerant canisters and abandoned HVAC units — left on roofs after an air conditioning repair visit.
Small debris can cut into the roof if the debris is stepped on; large debris will work its way into the roof membrane during the hot months of the year. Sign installers routinely install conduit through the walls without properly sealing the penetrations. The water that gets into those penetrations works its way through the walls and into the building, disguised as a roof leak. Window washers and painters hang access equipment over the side of the roof, kick flashings and damage parapets, allowing leaks to occur. All of these groups of people can wreak havoc on base flashings, which get kicked, punctured with tools and machinery, and have mechanical equipment run up against them.
Owners contribute to the early demise of their own roofs by not properly maintaining them and failing to repair small problems, before they become big ones.
Special Defects in Roofing Materials
Splice shingles used to keep material moving during the manufacturing process should be discarded but they almost always end up installed on the roof.
Blisters in shingles wear off from weather or foot traffic, becoming pits, causing moisture absorption.
Aesthetic or Cosmetic Roofing Issues
Some consumers have concerns with how their shingles look on the roof as much as with how long the roof will last. Roofing manufacturers offer a wide variety of products which give different “looks” and shadings. It’s possible that in addition to site and installation conditions, variations in manufacturing process (granule adhesion, bleed-through) can affect how the roof looks from the ground. We’ve also investigated client concerns with shadows appearing in early morning or late afternoon which show variations in the roof surface. (Some shadows which are only of cosmetic nature may be caused by slight buckling or unevenness in the roof decking and may not indicate a structural or durability concern.)
If you have particular concerns about roof appearance ask your roofer if s/he can direct you to a house where the product which interests you is already installed. Remember that site differences (orientation to sun, shade trees, height above ground, roof pitch, and probably other factors) may make shingles look a bit different on your house.
Roofing Warranties – Valuable or Worthless?
In certain instances specific roofing products have shown common early failure, failing in a characteristic pattern which is easily identified (such as the thermal splitting defect. Some manufacturers offer limited warranty coverage of their product. Many roofers also guarantee their work to be free from leaks, but usually for a time period substantially shorter than the manufacturer’s rated life of the roof material.
In cases which we’ve handled recently involving thermal splitting or tearing of fiberglass-based asphalt shingles, some manufacturers (such as GAF) offer a limited product warranty. Following a fairly involved claims procedure requiring documentation, photographs, and a sample of damaged material the manufacturer may elect to warrant the roofing material on a pro-rated basis depending on the age of the roof and its warranted life. Sometimes the manufacturer’s warranty covers only material cost, not installation cost (labor, demolition, removal of old materials) unless the roofing contractor chooses to extend such coverage.
The cost of roofing material is not the main ingredient in roofing cost. Labor and possibly disposal of old roofing material are significant costs. Out of concern for future roof life, some roofers are reluctant to install new roofing atop failed material even where additional layers of roofing are permitted by local codes.
Some homeowners are reluctant to install as new roofing the same product which failed early in the first place. Manufacturers might have changed the formulation of the product to improve durability, but they are understandably reluctant to say so, out of concern for increasing product liability. Without assurance from the manufacturer that a product which failed early has been modified to correct the problem, we advise our clients to consider using alternative products with design and performance expectations having a better track record.
Staying Out of Trouble
Preventing problems begins with the design of the roof and choice of materials. The roof membrane chosen should reflect the characteristics of the building. For instance, if there will be a lot of foot traffic, the facility executive should plan on using a system that will be resistant to such damage. If the roof is wide open and there will be a great deal of thermal movement in the structure, a stretchable material such as an EPDM membrane is a better choice than a system that has limited elongation capabilities.
Details must be carefully thought out prior to installation. For example, a transition from a gravel stop to a parapet is a poor building design that must be compensated for in the roof design. A metal transition piece can help alleviate problems that occur as a result of differential movement and different directional movement between the gravel-stop portion and the parapet portion. Correcting slope-to-drain problems should be determined at the design stage.
Second, the roof must be properly installed. This means using dry materials and installing them according to the design details or manufacturer’s requirements. Expansion joints have to terminate in a way that the end of the joint will still compensate for building movement. This means that there should be no material crossing the joint — not gravel stops, not copings, not membrane and certainly not roofing cement — that cannot flex or move with the movement of the structure. Seams should be adhered.
Finally, the roof must be maintained. Roof access should be limited to only those who need to be there. Keep smokers, lunches and sunbathers off the roof. Not only will the cigarettes burn holes in the membrane, the foot traffic will damage the surface and cause the roof to fail prematurely. Owners should monitor the activity of sign installers and window washers to be sure that they are not damaging the roof as they work. New HVAC installations should be flashed not by the mechanical contractor but by a competent roofing contractor to be sure that the penetrations are sealed.
The roof itself should be examined twice a year and drains cleared and roof debris removed. All small problems like punctures and sealant failures should be addressed at this time to be sure that they are not causing problems that will lead to failure. A roof’s life is finite, but it doesn’t have to be short lived. Some common sense when designing the roof, some attention to detail when installing it, and some care when using it will maximize its life.
Tampa Home Inspector
