From our many discussions with contractors over the years, we’ve learned that roof-over installation introduces an increased risk of workmanship errors. Moreover, a tear-off will reveal defects in decking that might otherwise go undetected. We have also learned that a growing number of contractors recommend a tear-off to their customers because they believe that a roof-over installation will “cook-up” and deteriorate the asphalt more quickly than will a clean roof installation.
Of course there are arguments in favour of doing a roof-over as well. For example, two layers of roofing provide redundant protection against leaks. Also, by allowing the original layer of roofing to remain, the cost of the job and the burden on landfills is reduced.
On balance, we are convinced that the argument for tear-offs and clean roof installations is persuasive for ensuring the highest possible quality finished roof system.
The roof deck is most vulnerable to leaks where it meets a vertical wall, at penetration sites such as a soil pipe or chimney, or at changes in slope such as at a valley, saddle, mansard, hip, or ridge. This vulnerability is due to:
- Deferential movements (e.g. the roof deck moves but the chimney does not).
- An accumulation of turbulent water (e.g. in valleys and on the high side of chimneys)
- An accumulation of melting snow or ice (e.g. in valleys and on the high side of chimneys)
- Breaks in overlapped shingles (e.g. at hips and ridges)
Flashing is installed at these locations to bridge adjoining structures and prevent water penetration. Flashing materials include sheet metal; cements, caulks, and sealants; and flexible sheets such as waterproofing shingle underlayment. At hips and ridges the cap shingles, not normally called flashing, serve the same function.
Leaving out ice-dam backups and catastrophic damage from severe storms, old age, or gross manufacturing defects, leaks are most likely to originate at a flashing that has failed or was improperly installed.
Many shingles manufacturers do not require that shingle underlayment be used under their shingles for the standard shingle warranty coverage to be in effect on slopes of 4/12 and more. However, when we look at the performance of the roof system a as whole, underlayment has a legitimate role to play.
Underlayment is considered to be an important component in the CSA (Canadian Standards Assocation) and the UL (Underwriters Laboratories Inc.®) as fire resistance classification. It can provide back-up protection in case of a shingle blow-off, and during the installation of the shingles it can keep the unshingled decking dry. For these reasons, and also because many contractors will say that they and their customers believe it is an important part of the roof system, most, if not all, shingle manufacturers agree.
Typically, underlayment is required when applying for extended warranties or when roof system installations are performed by roofing contractors who have received a manufacturers seal of approval as a quality contractor.
On slopes below 4/12, down to 2/12, the risk of leaks is great, caused by phenomena like wind-driven rain and capillary action that can make water flow uphill, or by the backup of water behind ice dams. To reduce this risk, a redundant system – called shingle underlayment by its manufacturers – is applied beneath the shingles. Shingle underlayment traditionally known as tar paper and roofing felt, is a roll product applied over the roof deck before the shingles are installed.
The term “underlayment” can cause confusion because there are other materials in the construction trade called underlayment. One grade of OSB, for example, used as a flooring sub-base is called underlayment. The OSB on a roof deck is not shingle underlayment. It is properly termed roof sheathing and must be rated by the American Plywood Association as such.
On the other hand, not all shingle underlayment is the same. There are two critically different grades: water-resistant and waterproof.
Water-Resistant Underlayment was invented to keep the roof decking dry until shingles could be applied. Applying this underlayment is called “drying-in the roof”. It was also useful as a separation sheet between the roof sheathing boards and the asphalt shingles before OSB and plywood sheets were used as roof decking. This separation was important because direct contact with resin pockets in the pine planks caused the asphalt to degrade prematurely.
Intact water-resistant underlayment sheds most of the water that falls on it, but its water resistance is temporary. As the sun degrades, the exposed asphalt the material begins to dry out, absorb more moisture, lose its strength and eventually tear. The less asphalt used to saturate the underlayment sheet during manufacture, the shorter its life. Since asphalt is the most expensive component of shingle underlayment, lower-priced materials have less asphalt and a shorter life when exposed to the sun and are also subject to severe wrinkling when wet or even just damp.
Water-resistant shingle underlayment is not warrantied by the manufacturer. It is an expendable material because much of its water resistance is destroyed during the installation of the shingles by driving hundreds of nails through it.
Until recently, only two grades of water-resistant underlayment have been available: Number 15 (standard) and Number 30 (heavy-duty). In recent years new categories have appeared known as premium and high-performance shingle underlayment. These materials are less likely to wrinkle when dampened. The CertainTeed Corporation makes a product in this class called Roofers’ Select. GAF, another manufacturer, produces one called Roof-Mate.
Waterproof Underlayment is an entirely different product that’s used in locations such as eaves and valleys that are most likely to leak under extreme conditions such as high winds, heavy rains and ice dams. This material is known as Waterproofing Shingle Underlayment. It is self-stick modified asphalt on a glass mat reinforcement. The cost is much higher than standard water-resistant underlayment because of its high asphalt content and polymer modifier. These products come with warranties against leaks and are not destroyed when nails are driven through them.
On low slopes where the risk is water running uphill, or in valleys where blockage from storm debris or ice dams can cause trouble, waterproof membrane is reliable insurance against leaks when used according to the manufacturers’ instructions. In all cases the product must be applied to a clean, dry roof deck. Examples of the variety of product types in this class of waterproof membrane:
- CRC – Storm Tamer
- NEI – Granular Ice & Storm Seal
- Grace Ice & Water Shield
- CertainTeed – Winter Guard
- ELK – Traction Grip
- GAF – Weather Watch
- IKO – Armour Gard
- Bakor – Eaveguard
- BP EMCO – Grip Guard
- Soprema – Lastobond
Roof systems go way back. The asphalt composition shingle is a modern version of a shingle system invented as far back as the Egyptian dynasties, but no one can be sure of its origin.
Wood shingles and shakes were probably the first shingles used in America by the colonists who brought the shingle concept from Europe. Slate remains common throughout Europe and the USA. Thatch is sill used in Britain and elsewhere in Europe. Clay barrel tiles and hand-formed roofs made from malleable metal go back to ancient Greece and Rome and remain in common use. Each of these roofing alternatives have cost, appearance, availability and performance characteristics that affect their desirability for a homeowner. Composition asphalt shingles are a modern addition to the roofing material inventory, and widely used in the USA. Overseas, composition shingles are not so widely used.
The principle behind shingling is ancient and proven: to keep water moving down sloping roofs until it runs off and away from the house. It doesn’t matter precisely what material is used so long as the slope is adequate. Materials don’t even have to be waterproof if you have enough redundancy. Thatched roofing and wood shakes are examples of materials that are not waterproof but nonetheless shed water.
So, the first principle of shingle roofing is: Keep the water running off the roof at the eaves. Anything that interferes with that principle introduces the possibility of a leak. Steep roof slopes are the foundation for an efficient water run-off. The lower the slope, the greater the risk that water can somehow back-up under the shingles.
For that reason no modern shingle manufacturer will approve the use of their materials in a shingle roof system on a slope below 2/12.
Cracking Through Reinforcement
Depending upon the style of shingle, the normal weathering characteristics described earlier may be a sign of more serious problems. For example, cracks across a typical three-tab shingle may be a sign of a weak reinforcement. This type of cracking threatens the waterproofing integrity of the roof and needs to be addressed immediately.
For the overlayed-style shingle, on the other hand, cracks that are restricted to the un-reinforced decorative built-up are the result of normal weathering and do not compromise the long-term performance of the roof system.
Granule Loss Exposing Asphalt
Large areas of granule loss that expose the underlying asphalt place the shingle at risk of premature failure because UV rays can now get to the asphalt layer.
In situations in which hail has knocked off large areas of granules, you can expect the life of your shingles to be appreciably reduced due to the effects of ultraviolet radiation from the sun. Shingles with open blister in which the asphalt becomes visible are also at greater risk for premature failure.
Just as the human body ages and changes appearance over the years, so too will a roof. Due to the severity of the roof environment, even a one-year-old roof may look different from a roof that was just installed. While cracks or blistering may first be noticed at close range (as from a ladder when cleaning the gutters), please be mindful that these normal weathering characteristics may not be visible when the roof is viewed from the front lawn or driveway. And if the problem is not severe and the shingles are still providing the protection intended, then it is not a cause for alarm.
A roof is an important investment, since it literally protects the whole house from the elements. However, there are no magical creams or ointments to prevent a roof from aging.
When a new roof was installed, friends and neighbours may have remarked how it enhanced the beauty of the home. However, research indicates that aging begins soon after the shingles are installed and progresses rapidly during the initial curing phase of its life cycle. During this stage, granule loss may occur, small blisters may develop or the shingles may curl slightly at their edges. You may even notice that this curling is more pronounced during cold weather and the shingles may lie flat as temperatures rise. The good news, however, is that after this curing stage the shingles enter a long period of slow aging, which lasts for the major portion of the shingles’ natural life.
During the “mid-life” period, aging continues at a much slower rate. The cracking or granule loss still occurs, but does not increase at a noticeable rate. Only after this long period of “mid-life” does the aging process begin to accelerate once again as the shingles enter their declining years. It’s during this period that homeowners normally think about replacing their roof.
You may be asking yourself, “What can I expect a roof to look like as this aging process takes place?” One or more of the following conditions may occur over time:
As the asphalt hardens over time, the granules which were once securely embedded begin to break away. Occasionally you may have seen the coloured granules in gutters. Also, as this hardening advances, the asphalt layers begin to shrink. Of course, all of this is occurring at a microscopic level and is not something which will be noticeable on a daily basis. As the asphalt layer shrinks, it is being countered by the shingle reinforcement, which resists shrinking.
We now have a situation in which the top and bottom coatings are shrinking and the reinforcement is remaining stable. As a result, the edges of the shingle may begin to curl over time.
Another manifestation of the normal aging process may be the development of surface cracks. For example, as the flexibilizing oils of the asphalt are depleted due to heat, the shingle becomes more brittle, to the point where surface cracking may appear. The stresses created by thermal shock and the movement of the roof deck also increase the likelihood of surface cracking.
During the course of natural weathering, small bubble-like raised areas known as blisters may appear on the surface of the shingles. The blisters may be small and pea-sized or as large as a quarter. The blister may be open, exposing the asphalt, or closed. Blisters frequently result when minimum ventilation requirements are not met.
Finally, over a period of time, shingles may develop dark brown or black streaks that are sometimes mistaken for soot, dirt, moss or tree droppings. In actuality, this discolouration may be caused by algae growth. Although most roofing systems are susceptible to algae discolouration, it is most readily visible on white or light-coloured shingles.
Consider the conditions a roof must endure. First there is the intense heat of the sun, which scorches the surface of the roof and raises rooftop temperatures 50º – 70ºF above ambient temperature. The sun’s rays are relentless, especially during the early afternoon hours. In addition to heat, the sun is the source of ultraviolet radiation, which has been shown to degrade and accelerate the aging of the asphalt layers of the shingle. If not for the protective layer of coloured granules, roofing shingles would fail very quickly. Other factors such as moisture, pollution and physical effects (roof traffic, hail, snow loads, tree limbs, etc.) all contribute to the aging and degradation of roofing shingles.
Seasonal and weather changes also play a role in the aging of asphalt roofing shingles. For example, consider the common situation in which the roof is bathed in the intense heat of the summer sun. On such a day the rooftop may reach temperatures in excess of 160ºF. Now imagine a cold front sweeping through the area, bringing with it the violent thunderstorms that are a common occurrence during the sweltering days of summer. Almost instantaneously, the rooftop temperature drops 60º – 100ºF as it’s pounded with a summer shower. Thermal shocks such as this cause the roof deck beneath to expand and contract, placing a strain on the shingles. Year after year this process is repeated, resulting in cyclic fatigue of the shingles.
In addition to all of the climatic and external variables that can impact the performance of a roof, consider the internal factors that negatively influence the performance of roofing shingles. Research has confirmed that an improperly ventilated air space inhibits air movement and under most circumstances increases moisture content in comparison with properly vented attic air spaces. Heat shortens the shingles’ life and moisture causes deck movement and/or deterioration, which ultimately affects the performance of shingles.
As you can see, the roofing environment is a hostile one with many factors influencing the longevity of roofing shingles. The natural aging process begins as soon as the shingles are installed on a roof. Day after day the shingles are exposed to the elements – sun, rain, heat and cold. A roof never has a “good” day.
Asphalt is one of the primary ingredients in roofing shingles. Its purpose is to provide the waterproofing integrity for the roof. Secondarily, the asphalt holds the coloured granules in place and contributes to the overall strength of the shingle. Asphalt, which is derived from petroleum, contains the oils that provide ductility and pliability to the shingles. During the lifetime of the shingles these begin to rise to the surface, where they are washed away by rainwater. In an attempt to restore equilibrium, new oils surface and the washing process continues. Also, the intense heat of the roof oxidizes or hardens the asphalt over time.
Wind is a major threat to a shingle roof system. Shingle sealant, drip edge, the construction of the shingle itself, and using proper fastening techniques are the primary defenses against wind damage.
Heat – A Natural Enemy of Asphalt
Heat, along with ultraviolet light, causes asphalt shingles to age through chemical changes that stiffen the asphalt. Initially, shingles are protected from ultraviolet light by the granules embedded in their surface. As long as the asphalt stays flexible the granules will stay in place. Eventually, however, the shingles become brittle and the granules break loose and gradually wash away.
Excess heat accelerates this aging process, causing the shingles to become prematurely brittle and show all the signs of aging, such as cracking, curling, clawing, and spalling. The aging shingles lose their granules at a faster and faster rate and subject them to even more rapid deterioration from ultraviolet light.
Fortunately, accelerated shingle aging can be slowed by reducing the heat from directly below the roof deck. Proper attic ventilation is the best way to achieve this objective and is a key component of the shingle roof system.
Roof venting allows fresh air into the attic space and lets older air cycle out. Soffit vents allow the fresh air in, which will travel up through the attic space as it warms and escape through the high venting. Without adequate and un-obstructed soffit venting to allow fresh air into the attic space, air becomes stagnant and heated which can lead to condensation (sometimes resulting in leaks), mould, damaged wood, and premature wear to the shingles. In the winter, a hot attic will cause snow to melt at higher points on the roof. Water will run down to the eaves and gutters, re-freeze and create ice dams. Ice dams will back up, often lifting the shingles, causing leaks and potential interior damage.
Attic ventilation can be achieved in a number of ways, and all homes should have high and low venting. High venting can be achieved with either ridge venting (where suitable) or by “mushroom” style roof vents. Low venting is almost always through vents located in the overhang or soffits. Soffit vents allow for air movement from the lowest part of the attic space. DeLuca Roofing Inc. will include an adequate amount of “high” venting in our quotation based on the size and design of your roof system. It is recommended that the soffit venting be assessed to ensure they are not blocked by insulation, or otherwise obstructed and that there is sufficient venting surrounding the home.
Attic Ventilation: The attic temperature should be the same as the outside air. An attic that is kept well ventilated will keep the exterior of your roof uniformly cold. If your roof stays cold, the snow will not melt from the bottom and the risk of ice damming will be minimized. Soffit venting should be clear and unobstructed to allow fresh air to cycle in and allow the warm air to escape through the upper roof vents. Sufficient soffit ventilation surrounding the house is necessary. Inexpensive Styrofoam baffles are recommended to keep the soffit vents clear of insulation to allow for proper air uptake into the attic space.
Reducing Heat Loss into the Attic: If a house has many warm air leaks, it may be impossible to add enough attic ventilation to overcome the resulting heat build up. Addressing the causes of warm air leaks in the attic is also very important in the prevention of ice damming. Listed below are some common problem spots that can be addressed to minimize warm air leaks into the attic space:
- Attic access hatch – an attic hatch door needs to be both insulated and weather-stripped
- Insufficient attic insulation – An attic that is insufficiently insulated will allow heat from the interior of the home to penetrate into the attic space.
- Potlights – Potlights are mounted directly into the ceiling/attic space and require the ceiling to be cut open causing obvious voids for warm air to penetrate. Pot lights generate a lot of heat and could pose a fire hazard if insulated improperly. It is recommended that you contact a professional to ensure any potlights are insulated properly.
- HVAC Registers – If the house has ductwork running through the attic the ductwork should be well sealed and insulated.
- Other ceiling fixtures – Ceiling mounted electrical devices like lights and bathroom fans should be sealed at their boxes.
Poorly placed eavestroughs: Poorly placed eavestroughs prevent snow and ice from shedding off the roof properly. This is less of an issue on its own, but a contributor when other factors like poor ventilation exist.
Recent changes to mechanical equipment in the home: An upgraded mechanical system (i.e. upgraded furnace system) can cause negative air pressure in the home particularly if the contractor did not pay careful attention to the required fresh air intake required for the appliance. During the course of a new system installation, the vapour barrier in the attic may also have been breached causing more warm air leakage in the attic.
A combination of any or all of the above factors can greatly affect the risk and severity of an ice dam occurring on your roof.
A Home Energy Audit can assist you with detecting problems in your home or attic that may lead to problems with ice damming, and can provide recommendations to improve the energy efficiency in your home. For more information you can go to The Ontario Ministry of Energy website at www.mei.gov.on.ca
Although removal of the ice would seem to be a solution, there are no practical ways to remove the ice without the potential of damaging the shingles or other roof components. There is also a great risk for personal injury. The shingle manufacturers warranty may also be rendered invalid as a result of ice dam removal.
Due to the factors involved in the causes and formation of an ice dam, DeLuca Roofing Inc. cannot be held responsible for leaks or damage caused as a result of ice damming.
An ice dam is a ridge of ice that forms on the roof as a result of a freeze-thaw cycle. When heat escaping from the attic starts melting the snow on the roof, the water flows under the snow and re-freezes when it reaches an unheated portion of the surface – usually at the eaves. As changing temperatures cause freeze and thaw cycles, the ice dam grows and gets thicker and it starts to spill over the eaves and cause icicles. In the meantime, water is prevented from flowing down the roof and will eventually back up finding its way under the shingles and into the attic and living space of the home causing damage to walls, ceilings and insulation. A thick ice dam can damage roof flashing, fascia and soffits and can even shift vent stacks and create gaps that allow for even more water to seep in through the roof.