INTRODUCTION

IR P/PM (infrared predictive/preventive maintenance) is not limited to annual infrared surveys of electrical switchgear. For instance, infrared thermography can be a very effective tool for roof asset management. IR roof moisture surveys are performed on roofs to quantify extent of roof moisture (water) that is inside roof system. Infrared thermography is not leak management. No matter how water got into substrate, purpose of this type of survey is simply to find and document where water is located. Extending life of a roof will save owner expense and aggravation of re-roofing or re-covering. Re-roofing means that roof is taken down to decking and replaced completely. Re-covering means that waterproofing layer(s) are removed, wet insulation is removed and replaced and a new waterproofing layer is put down. The cost of an infrared roof moisture survey is three to five CENTS per square foot. It cost between three and five DOLLARS per square foot to repair/replace roofs, so knowing exact location of subsurface water is extremely useful information, since only those areas that are damaged need to be repaired. This information is used to plan budgets and when needed, as a bid document for contracting repairs and/or replacement of roof.

Keywords: Infrared, Thermography, Roof, Roof Asset Management, Infrared Roof Moisture Survey.

ROOF MAINTENANCE IN GENERAL

The ravages of sun, wind, rain, snow, chemicals, leakage, rapid changes in temperature and time - will eventually cause every roof to fail. Some roofs last 40-50 years…when they are well maintained. Owners may believe that a roof warranty will somehow protect them from having to do maintenance. Not so, as roof warranties are written by roofing manufacturers for purpose of protecting themselves from liability. For example, often a warranty is written so that if improperly installed or defective roofing materials are used on a roof and water leaks into electrical switchgear room causing an explosion, roofing manufacturer will replace materials, roofer will reinstall materials, but building owner has to pay for replacement of switchgear and any downtime that resulted from failure. Also, roofer’s and roofing manufacturer’s liability, in case of roof failures are also reduced by vaguely written roof warranties, which do not define words like "regular" or "routine" maintenance. Not accepting roof warranty is not answer, since roof will not be installed unless owner agrees to warranty. To eliminate these problems, building owner should have an agreement with a qualified roofer or roof consultant to inspect and maintain roof (in accordance with terms of warranty) at least once a year.

Waterproofing problems manifest themselves in two ways: Leakage and entrained moisture contamination. Leakage is pretty simple, although leak inside building rarely directly relates to exact spot on roof, since water flows down slope of roof to a spot that is not sealed and into building at that point. Most leaks occur where waterproofing is sealed or where there is a penetration of roof. Since most types of roof systems absorb some amount of water, it is harder to find exact spot of water contamination in insulation because it may not leak into building until it has absorbed all water it can hold. There are three types of surveys that are used to find water in a roof. Nuclear gauges-which count neutrons, capacitance meters-which measure resistance, and infrared-which measures heat. Both nuclear gauges and capacitance meters are used to take spot readings on a 10' X 10' or 20' X 20' grid on roof. These measurements are used to extrapolate where water is from readings obtained from gauge. They are good for types of roofs that do not gain or lose much solar energy and therefore, do not lend themselves to infrared.

BASICS OF INFRARED ROOF MOISTURE SURVEYS

During day, sun radiates energy onto roof and into roof substrate, and then at night, roof radiates heat back into outer space (See Figure 1). This is called radiational cooling. Areas of roof that are of a higher mass (wet) retain this heat longer than that of lower mass (dry) areas. Infrared imagers can detect this heat and "see" warmer, higher mass areas, during "window" of uneven heat dissipation.

Figure 1) Areas of roof that are wet retain heat longer than dry areas.

Some roofs and insulation types or combinations do not absorb any water. These roofs leak straight into building. Even roofs, which have insulation types that do absorb water, some do not exhibit a good infrared signal, primarily for two reasons. 1) The surface is too reflective, and/or 2) roof’s ballast is so thick (or dense), that daylight radiation is not absorbed into substrate (insulation), therefore it cannot be emitted back into atmosphere at night. Even with a strong infrared signal, factors on roof can affect analysis and interpretation of data. Some of these factors: water between multiple layers, old patches, heavy flood coats, reflective coatings, heat-producing equipment under roof –or heat blowing down onto roof, stains, ponding water on roof, heavy build-up of ballast at parapet walls and along edges, etc. These roofs should be inspected by other methods as described above.

WALK-ON INFRARED ROOF SURVEYING