Flat Roofs – Detect Defects with IR Thermography
Carl Brahe, Inspection Perfection inc
The biggest concerns with any roof are: Does it leak? And when will I have to replace it? Flatroofs cost more to install and maintain and have a much shorter average lifetime than slopedroofs. The greater the pitch of the roof the longer it’s likely to last. Sharper pitched roofs will have lighter loads from snow build-up and water will shed faster.
Flat roofs have an estimated average life of around 13 years. In reality, some flat roofs willlast many times the average depending on maintenance. Some will be prematurely replaced due to deferred maintenance or defective workmanship or materials.
Water intrusion is the ultimate enemy of any roof. Once water penetrates a flat roof, it is not likely to dry naturally. When moisture levels exceed 19% for 48 hours mold and rot begin to consume building materials. These fungi will continue to grow until the moisture level drops below 19%.
Leaks in a flat roof can be very difficult to find and can cause extensive damage before being discovered. Many flat roofs systems are made of layers of roofing. When water penetrates the outer layer, it will seek the closest downhill defect in the next layer of roofing to drain through. This may be on the other side of the building from the top layer leak. The water will find its way through all layers eventually and leak into the decking and continue downward.
Many leaks in flat roofs can be discovered by IR thermography before extensive damage happens. IR thermography uses the temperatures on a surface to create an image. IR cameras detect slight variations in surface temperatures. Different building materials hold and release heat at different rates. Wet building materials hold and release heat slower than dry building materials. The various temperatures of different materials, wet and dry, transfer to the surface. Under the proper conditions, surface temperatures can reveal what’s inside roofs and walls using thermal imaging.
This thermograph shows water under flat roofing. Exterior thermal images of roofs are taken one hour after sunset when the surface has had time to cool and reveal the water which will be a higher temperature than the rest of the roof. Wet building materials cool slower than dry building materials.
Thermal image of moisture from the underside of a concrete roof deck. Interior thermal images are taken in the morning.
Defects discovered and repaired quickly can save substantial amounts of money over the life of a building. Flat roof replacements are estimated at $2-20/sq ft. IR thermography can provide information about a roofs condition that might allow quicker repair or replacement of only defective areas. Generally, if a roof is less that 1/3 defective, it can be repaired instead of replaced. Quicker repairs equal a longer useful life and less expense at replacement time.
A flat roof is not actually flat. A slight slope is built in to cause water to run off. In most flat roofs, ponding after a rain or snow will develop with age. Standing water will eventually work its way through roofing materials, particularly at joints and flashing. These materials contract and expand from changes in weather. They become brittle, dried and cracked by wind, the effects of UV rays and other natural influences. Ponding and leakage results when the roof no longer sheds water effectively.
Human activity is one of the most common causes of flat roof damage. When roof top heating and cooling units are installed damage can occur to roofing. Ladders or equipment loading may scar or break through roofing allowing leaks. Equipment bolted to the roof may be poorly sealed or even left unsealed. Over 60% of roofing defects come from human activity or poor workmanship.
Ninety percent of roof defects come from flashing leaks. Flashings leak from:
- Poor design
- Poor workmanship
- Improper materials
- Damage from impact
- Debris build up
Almost half of all roofing defects are the result of poor workmanship. These defects can be particularly tough to discover.
The leak this ceiling, shown by IR thermography, was caused by two nails dropped under the roofing during construction.
The leak was discovered using IR thermography avoiding tearing off the whole roof to find the leak.
The difference between a short-lived flat roof and a long-lived is maintenance, assuming your roof was properly installed using appropriate materials. The more deferred maintenance, the shorter the useful life and the more expensive the repair/replacement.
One of the most important maintenance tasks is keeping water from pooling. If water doesn’t drain properly, a system of siphons can be manufactured with parts from the local hardware store to move water from low spots. Water may also be broomed off where sweeping does not remove the protective layer of gravel. The quicker you get the water off the less chance there is of a leak developing.
Debris on the roof can clog drains and scuppers leading to ponding. Keeping the roof free of debris also removes organic matter that may decay building materials in contact with it. The roof should be cleaned a couple times a year. More if there are overhanging trees. A roof should be inspected after every major storm for debris and damage.
Some flat roofs depend on a covering of gravel to protect the underlying waterproof layers. The substrate can be uncovered by wind and human activity leaving materials vulnerable to rupture or natural decay. Left exposed to the sun, these materials dry shrink and crack allowing water to enter. Replenish the gravel when its layer becomes thin.
Roofing materials can blister when water is trapped beneath and heated by the sun. These blisters need to be cut out and repaired as soon as possible to avoid further water penetration.
When you notice a leak it is time to call a competent roofing contractor for repairs. You may find it more efficient and convenient to have your roof inspected twice a year, using IR imagery where appropriate. Some roofing material manufacturers void warranties if bi-annual inspections are not performed and documented. Inspection Perfection Inc provides this service with a discount for multiyear contracts.
A building’s roof is its first line of defense against weather and its aging effects. The roof is probably the biggest single item replacement expense that you will have if you own any building long enough. Regular inspection and maintenance pays. The better the roof is maintained the longer it will last and the less it will cost to replace at the end of its useful life.
Copyright 2003 all rights reserved
Utah’s Commercial Flat Roof Consultants, IXL Infrared Management