Roofing Experts | ACS | NorCal

The Top 7 Causes of Commercial Flat Roof Failure and How to Fix Them

Roofs are the most important part of your building, and they’re a large investment. Here are 5 natural forces and 2 human actions that cause your roof to fail prematurely.


If you’ve ever stuck your hand out the window while traveling 50 mph down the freeway, you know wind is a force to be reckoned with.

It can damage your roof two different ways. The first is obvious, but the second isn’t.

Wind is another name for changing air pressure. Cool air is dense and heavy. It pushes under warm air which rises. We perceive that movement as wind.

When wind strikes loose edges on your roof, like metal flashing, it can get under those edges and lift them up, doing damage over time. But wind has a stranger way of causing damage to your roof.

There’s a reason roofs have uplift ratings. When that wind comes over the edge of a roof, the airflow also creates a vortex of negative pressure that tugs at the edges of the roof.   The damage is usually negligible, but it is cumulative and can be a problem as the roof gets older.

Now, let’s say that wind blows across a roof at 90 mph. As it does, it becomes a giant vacuum, creating enough of a negative pressure that it lifts your roof up. Furthermore, as the wind gusts, it lifts the roof up, then lets it fall down. This constant lifting and dropping action can also help work to separate the roof from the deck if it’s not properly attached.

The solution: Secure all perimeter and metal flashing properly. Ensure roof seams are tight and properly welded.

Heating and Cooling

Heating and cooling effects are working at your roof membrane every day.  Heat causes expansion and cooling causes contraction, with one curious exception, which we’ll get to shortly.

Have you ever bent a piece of wire back and forth until it breaks? Expansion and contraction does something similar to your every day. If temperature is stable, like in the SF Bay Area, the wear and tear isn’t as great as the desert regions of New Mexico where the temperature can fluctuate much more throughout the day.

Here’s the kicker: Membranes probably won’t don’t become separated where they connect, unless there was a poor weld. But those membranes are attached to an underlying deck. If that’s plywood, chances are you’ll see splitting where the plywood pieces meet each other. If it’s a concrete deck that isn’t monolithic, the “seismic” forces at the edges of the slabs may also tear the membrane.

Solution: Reflective roof coatings keep the roof cool, minimizing expansion and contraction, and greatly extending your roof’s life span.

The Sun

The Sun emits electromagnetic energy of certain wavelengths that form the visible spectrum from red to purple. The most damage is caused by light at the edges of that spectrum that is invisible to our eyes. The light below red is called infrared. It’s what snakes “see” with their tongues. The light just beyond purple is ultraviolet, and it’s what bees see in flowers that tell them where to land.

Infrared(IR) light is sensed as heat. It causes expansion and its absence results in contraction.

Most ultraviolet light is caught and stopped by the ozone layer, which is why the sky appears blue during the daytime.   However, some of the ultraviolet(UV) light makes it through the Earth’s ozone shield to cause damages your skin and your roof.  You put sunblock on your skin to protect it but how do you put sunblock on your roof?

Solution: Granules and gravel capture or reflect UV or IR radiation, but they have problems. Either they have low reflectivity that gets worse with time, or they way a lot and have a high roof load.

Acrylic or silicone roof coatings are the best sunblock. They are lightweight and reflect 50-90% of all light. Their white coatings reflect both UV and IR, so they stay cool and resist damaging sunlight. The result? Your roof lasts much, much longer. One caveat is they do accumulate dirt and lose their reflectivity, so they may need to be periodically cleaned.


Water can damage your roof in several ways. If it gets under your roof membrane, it can cause dry rot, although most plywood is treated with chemicals to prevent this.

However, if water gets trapped in a pocket and expands, it can cause blisters that will become brittle and crack. If you live in a cold area where you get snow or ice, then you have a much bigger issue to worry about that’s caused by one of water’s most unique properties.

Almost every substance shrinks as it gets cold, but water expands, which is why ice floats on liquid water. Here’s why that’s a problem. When ice gets into any crack, no matter how tiny, it expands, wedging it open more and more over time. But there’s another form of ice that is even more destructive.

Hail can cause massive damage. Golf ball sized hail cracks tile roofs, which is why they are rarely seen in the Midwest. Even asphalt or TPO can be damaged by the impact of hail. Strangely the damage occurs at the base and in the middle of the membrane where it can’t be seen, causing damage that only becomes apparent later. This is a primary reason why why metal roofs are seeing explosive growth in the Midwest.

Another way water water damages your roof is even more insidious. Water weighs 8 pounds a gallon. If your roof has poor drainage, water ponding can add a lot of weight to a localized area that will slowly damage the underlying deck, causing it to sag, eventually resulting in costly structural repairs.

Solution: Metal roofs solve the problems of hail and ice formation. Proper installation and maintenance can address drainage problems that cause water ponding or blistering.

Two other factors shorten your roof’s life expectancy. They are the result of human actions, not natural forces, so they can be easily mitigated.

Improper Installation

If your roofer doesn’t know how to properly tie your roof into penetrations, it is more likely to leek.

Solution: Use a professional roofing company. Don’t cut corners to save money in the short run. Hire commercial roofing professionals, not residential companies claiming expertise in commercial flat roofing.

Lack of Maintenance

Like cars, roofs need maintenance. They need to be cleaned regularly so trash and dirt don’t clog drains and cause ponding. If your roof is more than ten years old, it’s getting brittle from years of sun, wind and rain. That makes it more vulnerable to expansion and contraction and is another reason you should get regular maintenance.

Solution: Have your roof regularly inspected. The NRCA recommends twice a year, which is a conservative estimate. Inspect your roof annually, especially if it is older than 10 years or has a lot of penetrations.


The two best ways to extend your roof life is regular maintenance and roof coatings. Maintenance prevents water ponding and maintains its ability to protect your building. Acrylic roof coatings reduce heat eliminating expansion and contraction. Their high reflectivity decreases UV damage, lowers energy costs, and increase durability. They’re lightweight and last up to 20 years and can be easily re-coated, whereas silicone coatings are much harder to re-coat.

Got questions or need a roof inspection? Please call us at (925)724-2324.

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