Fundamentals of Roof Inspections

This article is provided courtesy of Snell Infrared, a thermographic training company.

As summer approaches so does roof maintenance season. Infrared roof moisture surveys continue to provide vital information for the long term maintenance of flat roofs. With a national average life of only seven years, flat roofs are the most expensive component of a building.

Why such a short life? Workmanship problems lead the list of causes, followed by poor designs, material failures, and poor maintenance. Once a roof begins to leak water it is absorbed into the roof assembly, especially the insulation. Once wet, for all practical purposes, insulation never dries. In fact, the trapped moisture can quickly cause further serious degradation to the roof, including the rusting of metal decks and fasteners, reduction in insulating value, and decay of the membrane.

Many roofs last longer­twenty or more years is not uncommon. The secret? Good workmanship, design, materials, and a long term maintenance program. Twice a year visual inspections using a good checklist are considered essential to head off probl ems. But only infrared can quickly let you see the true condition of the insulation in the entire roof. When the roof does develop a leak­and even the best can­infrared surveys are used to locate trapped water. Because the leak is typically found to be within the boundary of the wet insulation, the wet area is marked for removal and repair. That keeps the roof in a dry condition, minimizing roof degradation, and extending the life of the roof.

How do you find wet insulation below the surface of the roof? When the surface itself is dry, including any gravel or ballast, a sunny day will warm the entire roof. Early in the evening, if the sky is clear, the roof will begin to cool down by radiat ion. Because of its higher thermal capacity the wet insulation will stay warmer longer than the dry and will be visible in the infrared imager (see photo below). The technique is particularly effective on roofs having absorbent insulation­such as wood fiber, fiberglass, and perlite­ where thermal patterns correlate almost perfectly with moisture. Infrared inspections of roofs with nonabsorbent insulations, common in many single-ply systems, are more difficult to diagnose because patterns are more diffuse.

The roof moisture survey must be conducted safely! Never go on the roof alone. Company or government regulations may require that you follow special safety procedures, possibly including wearing fall protection gear. Is it all worth it? Considering you can save your company over a $100,000 in an evening, you bet it is!

The limitations? Clearly successful inspections are weather dependent. The ideal conditions are sunny days followed by clear nights with low winds, making spring, summer and fall the best times to inspect. Surveys can be conducted in the winter if the roof surface is dry. Similar thermal patterns are enhanced by the building's interior heating sources. For large roofs, or where there are multiple buildings to inspect, consider hiring a contractor to conduct an aerial infrared inspection. Using a helicopter or fixed wing aircraft and high resolution infrared imager, aerial surveys deliver very high quality images of large areas in a short time. Many contractors overlay the infrared image on a visual image of the building to clearly show the areas of wet insulation. With the survey data in hand, prioritizing follow up rooftop inspections become a simple matter.

When a roof membrane has finally outlived its useful life, having a dry roof below it pays further dividends. The deck will be in much better condition. Disposal costs will be reduced because it will probably be possible to salvage some of the dry ins ulation. Leaving it in place and simply adding a new membrane can easily save $5 per square foot or more.

When should you conduct an infrared roof moisture inspection? New roofs should be inspected upon acceptance from the contractor­many are wet from the beginning. Ideally they are also inspected soon after a leak occurs in order to identify the extent of damage to the insulation. Typically inspections every 2-3 years will keep up with problems. Of course if known damage has occurred to the roof, an inspection on an earlier schedule is warranted. It is also important to inspect the roof prior to the expir ation of the warranty.

The techniques for conducting a roof moisture survey require some simple education and practice. It is one of the applications we cover thoroughly in our Level I courses. Many thermographers are using infrared inside their plants but are not yet using it on top as well, missing a big opportunity. For each year you can extend the life of a million dollar roof (100,000-200,000 square feet) past the seven year average, you are putting nearly $150,000 in the bank. That's worth going after!

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