Thermal shock occurs when changes in temperature happen so quickly that it stresses your roofing system materials. Rapid expansion or contraction can damage materials that have lost their elasticity. And since the different parts of your roofing system expand and contract at different rates, various simultaneous movements caused by quick, extreme temperature changes can cause problems, especially in horizontal-to-vertical transition areas.
Stress and strain can cause fissures that allow water into the system and in some cases a crack in the membrane that looks like an earthquake hit.
When you think about when extreme temperatures that can affect a roofing system you probably think about cold snaps in the winter. But thermal shock can occur all year long. Here in the South, thunderstorms can roll in and create temperature drops of 30 degrees in a matter of minutes.
Material life cycles and lateral movement
All materials have life cycles. Newer roofs aren’t that susceptible to thermal shock because they’re still flexible. But as the materials age, they begin to fatigue. They lose some elasticity and the ability to expand and contract at the same rate as when they were new. As a result, fatigued materials are more likely to incur damage during periods of extreme temperature changes. Typically, the older roofing system, the higher the risk of thermal shock.
In addition, different materials have different coefficients of thermal expansion and contraction, meaning one material will change size due to temperature changes differently than another material. So with a roofing assembly that consists of underlayments, insulations, adhesives, fasteners, and membranes, each of those materials has a different coefficient and will therefore move at a different rate.
Roofing systems already have lateral movement because materials are pushing and pulling against each other, so extreme temperature changes can amplify the movement and stress materials to the point where something can fracture. The more brittle any particular material, the worse the break can become.
Worst case scenarios
The worst cases of thermal shock occur when extreme temperature changes are most likely — in the dead of winter and during summer thunderstorms. Roofing materials at the end of their life cycle can literally split wide open. A sudden blizzard with arctic cold air in January followed by a warm front can do it and so can a fast-moving thunderstorm in June.
How can a storm in June cause thermal shock in metro Atlanta? Let’s say it’s a pleasant 75 degrees outside and sunny. If your roof is dark, it can easily be 30 or 50 degrees hotter than the air around it — even light-colored roofs can get much hotter than the ambient temperature. Then in comes a quick thunderstorm from Alabama and in literally 15 minutes there’s a temperature change of 30 degrees in the middle of that thunderstorm. Since the roof surface temperature is much hotter than the ambient temperature already, the drop in temperature in the middle of that storm is even greater. A sudden temperature drop of 45-50 degrees will stress the roof.
Signs that your roof is at risk for thermal shock
Hairline fractures, while inherent and common in the normal aging process of a roofing system, could indicate the roofing materials are starting to dry out, making them brittle and more susceptible to stress. However, just as an asphalt parking lot can have many small cracks that can be sealcoated to extend its life, hairline fractures don’t always mean your roof is about to fail and needs replacing.
The hairline fractures you want to pay particular attention to are those in the roof membrane itself (a sign that it’s reaching the end of its life cycle) and in areas where there’s a transition from horizontal to vertical. Sudden movement of materials in transition areas may loosen the flashing, which can create gaps that let in water. Transition areas to keep an eye include:
- Curbs flashings
- Parapet walls
- Pitch pans
- Pipe penetrations
Also carefully monitor drains, even though they’re horizontal, and any areas that have sealants applied.
Keep in mind that high-maintenance items like pitch pans have shorter lifespans than other roofing components and will usually need to be replaced before you need to re-roof.
What to look for on your specific type of roofing system
If your metal roof has exposed fastener heads, look for missing fasteners or fasteners that are stripped out. Thermal shock can cause movement that enlarges the holes, which can cause leaks. If fastener heads have grommeted washers, look at the condition of the washers — have they begun to disintegrate from age? Also check the penetration sealant condition, the water tightness of panels, and the details at all horizontal to vertical changes.
For built-up roofing systems, look for areas of gravel loss or migration, crazing (hairline cracks in patterns or networks), and blisters. You don’t need to move the gravel — the gravel will indicate where there’s a problem, similar to the way granular loss on asphalt shingles indicates a problem. For modified bitumen roofs, look for granular loss if your cap sheet has a granular surface or look for discoloration if the surface is smooth. If the black surface is starting to grey up, for example, then you have asphalt loss and your membrane is aging, making it more susceptible to thermal shock.
For TPO, EPDM and PVC roofs, check the laps (seams) and any openings or voids in laps. Inspect the surface of the membrane looking for punctures and starbursts — starbursts are typically the result of large hail. These are telltale signs of areas with a higher probability of experiencing a big fissure due to thermal shock.
If you have a black roof, these signs will be harder to find. And if you have a PVC roof, be aware that PVC has the ability to become brittle over time, especially when unreinforced.
Slate and tile roofs
Even though slate is rock-hard and tile can be brittle, they’re installed as individual pieces so these roofs are much less susceptible to thermal shock. As long as they were installed properly, each tile can move on its own so there’s little risk that extreme temperature changes will impact the integrity of the roof.
If you have a layer of engineered soil on top of your roofing system, your roof is at the least risk from thermal shock. The dirt significantly insulates the roof and is as elastic of a material as you can find (we’re not talking Georgia clay here — this is special soil). The vegetative surface neutralizes the risks caused by temperature change by design.
Warranty coverage for thermal shock
Check the fine print of your warranty to see if it covers damage from thermal shock. Some roof warranties, like some car warranties, are bumper-to-bumper while others barely cover anything. Penetrations and pitch pans typically are not covered by warranty but flashings at walls and curb may be covered.
How to prevent thermal shock damage
- Have a roof maintenance program
At a minimum, you should have your roof assessed twice a year — after winter and after summer. Four times a year is better, following the seasons. Your roof technician will take care or minor issues and look for extreme stress cracks that may mean something significant is going on. Skilled, experience roof technicians will assess and report on all of the inspection details mentioned above.
- Adhere to the manufacturer’s recommendations
Manufacturers know their products best so make sure to address the maintenance items exactly as the manufacturer recommends. This also ensures you don’t inadvertently void your warranty.
- Contact your roof maintenance contractor after a significant freeze and thaw or thunderstorm
Did that storm damage your roof? The only way to know is to look. Usually these kinds of inspections are included in your roof maintenance program. When your contractor has been maintaining your roof, they understand the system and how it performs so they’ll be able to notice changes and compare to photos from previous inspections, if necessary. If you don’t have a relationship with a contractor, expect to pay an hourly rate or one-time fee for the inspection.
Keeping up with roof maintenance will help you extend the life of your roof by as much as 25% and mitigate situations that could lead to thermal shock. If you’re familiar with this blog you know that Sentry Roof is constantly recommending that property managers and owners develop working relationships with a reputable roofing contractor — it will pay off in the long run.
Even new roofs need occasional maintenance, and as your roof ages it’s increasingly important for your roofing technician to be on the lookout for material fatigue. When your roof is approaching the end of its life cycle, a good roofing contractor will start talking to you about roof replacement options and the associated costs so you can work that into your budget. Depending on the situation, your roofing contractor may be able to recommend alternatives, such as a roof renovation or recovering the roof, to delay re-roofing while still protecting your property from risks like thermal shock.
Sentry Roof works closely with our customers to manage their roofs and have had many of the same customers for decades. We believe your commercial roof is an asset that should be managed just like your other business assets — it’s all about getting the most value and longevity from your investment. If you’d like more information on our services, including maintenance services or roof inspections, please feel free to contact us today.
Photo credits: Main photo: David Selby; snowy Atlanta: Henrick Christensen; anvil cloud: Ryan Keene