MRO Today - IR: Infrared thermography

IR
Infrared inspections save your roof's life (and your company serious cash!)

by John Snell and Jim Fritz

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

Why such a short life? Workmanship problems lead the list of causes, followed by poor designs, material failures and poor maintenance.

Once a roof starts leaking, the roof assembly absorbs water, especially in the insulation layer. For all practical purposes, wet insulation never dries. In fact, the trapped moisture can quickly degrade the roof, causing rust on metal decks and fasteners, insulating value reduction and membrane decay.

Many roofs last longer -- 20 or more years is common. The secret? Good workmanship, design and materials, as well as a long-term maintenance program.

Beyond the surface
Twice-a-year visual inspections using a good checklist are considered essential to head off problems. But, only infrared thermography can quickly let you see the true condition of the entire roof's insulation.

When the roof develops a leak -- and even the best can -- infrared surveys locate trapped water. Because the leak is typically found within the boundary of the wet insulation, the wet area is marked for removal and repair. This keeps the roof in dry condition, minimizing roof degradation and extending roof life.

How do you find wet insulation below the roof surface? When the surface is dry, including any gravel or ballast, a sunny day warms the entire roof. Early in the evening, if the sky is clear, the roof begins to cool down by radiation. Because of its higher thermal capacity, the wet insulation stays warmer longer than the dry insulation and is visible in the infrared tool's imager.

The technique is particularly effective on roofs having absorbent insulation -- such as wood fiber, fiberglass and perlite -- where thermal patterns correlate almost perfectly with moisture. Infrared inspections of roofs with non-absorbent insulations, common in many single-ply systems, are more difficult to diagnose since patterns are more diffuse.

Restrictions and limitations
Safety is a key component of a roof moisture survey. Never go on the roof alone. Company or government regulations may require you to wear fall protection gear and follow special safety procedures.

Weather also plays a big role in a successful inspection. The ideal conditions are sunny days followed by clear nights with low winds, making spring, summer and fall the best times to inspect. Surveys are possible in the winter if the roof surface is dry.

Also, thermal patterns are enhanced by the building's interior heating sources.

Consider outside help
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 a high-resolution infrared imager, aerial surveys deliver high-quality images of large areas in a short time.

Many contractors overlay the infrared image of the building on top of a visual image to clearly show areas of wet insulation. With the survey data in hand, prioritizing follow-up rooftop inspections becomes a simple matter.

When a roof membrane outlives its useful life, having a dry roof below pays further dividends. The deck remains in much better condition.

Disposal costs are reduced because it's possible to salvage some of the dry insulation. Leaving it in place and simply adding a new membrane easily saves $5 or more per square foot.

A matter of 'when,' not 'if'
When should you conduct an infrared roof moisture inspection?

Inspect new roofs upon acceptance from the contractor (many are wet from the beginning). Ideally, also inspect them soon after a leak occurs. This identifies the extent of damage to the insulation.

Typically, inspections every two to three years keep up with problems. Of course, known damage to the roof warrants inspection on an earlier schedule. Also inspect the roof prior to warranty expiration.

The techniques for conducting a roof moisture survey require some simple education and practice. It's one of the applications covered in many Level I infrared thermography courses offered by training companies.

Many thermographers use infrared inside their plants, but fail to use it on top as well, missing a big opportunity. For each year you extend the life of a $1 million roof (100,000 to 200,000 square feet) past the seven-year average, you save your company nearly $150,000.

That's worth going after!

John Snell is president and Jim Fritz general manager of Snell Infrared, a thermographic training company.

This article appeared in the June/July 2000 issue of MRO Today magazine. Copyright, 2000.