Aerial Inferred Roof
Moisture Surveys
by Gregory R. Stockton
Aerial Infrared Roof Moisture Surveys
INTRODUCTION
IR P/PM (infrared predictive/preventive maintenance) is not limited to
annual infrared surveys of electrical switchgear. For instance, infrared
thermo-graphy can be a very effective tool for roof asset management. IR
roof moisture surveys are performed on roofs to quantify the extent of
roof moisture (water) that is inside the roof system. Infrared
thermo-graphy is not leak management. No matter how the water got into
the substrate, the purpose of this type of survey is simply to find and
document where the water is located. Extending the life of a roof will
save the owner the expense and aggravation of re-roofing or re-covering.
Re-roofing means that the roof is taken down to the decking and replaced
completely. Re-covering means that the waterproofing layer-(s) are
removed, the 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 the
exact location of the 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 the roof.
Keywords: Infrared, Thermo-graphy, 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 the 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
the electrical switchgear room causing an explosion, the roofing
manufacturer will replace the materials, the roofer will reinstall the
materials, but the building owner has to pay for the replacement of the
switchgear and any downtime that resulted from the failure. Also, the
roofer's and roofing manufacturer's liability, in the case of roof
failures are also reduced by vaguely written roof warranties, which do
not define words like "regular" or "routine" maintenance. Not accepting
the roof warranty is not the answer, since the roof will not be
installed unless the owner agrees to the warranty. To eliminate these
problems, the building owner should have an agreement with a qualified
roofer or roof consultant to inspect and maintain the roof (in
accordance with the terms of the warranty) at least once a year.
Waterproofing problems manifest themselves in two
ways: Leakage and entrained moisture contamination. Leakage is pretty
simple, although the leak inside the building rarely directly relates to
the exact spot on the roof, since the water flows down the slope of the
roof to a spot that is not sealed and into the building at that point.
Most leaks occur where the waterproofing is sealed or where there is a
penetration of the roof. Since most types of roof systems absorb some
amount of water, it is harder to find the exact spot of water
contamination in the insulation because it may not leak into the
building until it has absorbed all the 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 the roof. These measurements are used to extrapolate where
the water is from the readings obtained from the 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 the day, the sun radiates energy onto the roof and into the roof
substrate, and then at night, the roof radiates the heat back into outer
space (See Figure 1). This is called radiational cooling. Areas of the
roof that are of a higher mass (wet) retain this heat longer than that
of the lower mass (dry) areas. Infrared imagers can detect this heat and
"see" the warmer, higher mass areas, during the "window" of uneven heat
dissipation.
Figure 1) Areas of the 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 the 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) the roof's ballast is so thick (or dense), that
daylight radiation is not absorbed into the substrate (insulation),
therefore it cannot be emitted back into the atmosphere at night. Even
with a strong infrared signal, factors on the roof can affect the
analysis and interpretation of the data. Some of these factors: water
between multiple layers, old patches, heavy flood coats, reflective
coatings, heat-producing equipment under the roof -or heat blowing down
onto the roof, stains, ponding water on the 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
To perform a walk-on or on-roof survey properly, a crew of three to four
people is needed: an experienced infrared thermo-grapher and helper, an
experienced roof consultant or roofer and the building owners'
representative for access and security. The crew walks around the roof
(s) and when an area of suspect moisture is found, the roof consultant
verifies it is wet and then the helper marks the edges of the area
directly on the roof with marking paint as instructed by the
thermo-grapher. The crew needs authorization and access to all areas and
levels of the roof (s) from either ladders or roof hatches and plenty of
time to collect data. The infrared images are stored on videotape or
digital media and printed (See Figure 2).
Figure 2) On-roof IR image.
The next day, the thermo-grapher goes back on the roof (s) to take
matching visual photographs of the marked areas that contain subsurface
moisture. The problem with on-roof infrared is that when one is standing
on the roof, eye-level is at best six feet over the surface. Even with
the best hand-held infrared camera available, there is virtually no way
to get large areas (800 sq. ft. blobs or 100' long striations) of
moisture contamination on the screen in one infrared shot. Taking
multiple shots is labor-intensive and makes the report confusing. When
performing on-roof surveys, many times "you can't see the forest for the
trees." Marking the roof is fairly easy, but it is very
difficult/time-consuming to produce accurate drawings of the wet areas
from painted lines on a roof. Often the drawing supplied by the owner is
outdated, incorrect or even non-existent.
AERIAL INFRARED ROOF SURVEYING
There is never a time when on-roof imagery is better than aerial
imagery. While the best IR imagery of a roof is taken from the air, the
same laws of physics apply to both aerial IR and on-roof IR…like a dry
roof, low winds and no rain on the night of the survey. Also, the
"window" when the roof is radiating heat differently from wet and dry
areas is longer with aerial infrared because slight nuances of
temperatures over large areas are distinguishable. The high angle of
view allows the aerial thermo-grapher to produce more usable imagery and
therefore accurate CAD drawings. The cameras that are used for on-roof
surveys are not of sufficient spatial resolution to obtain good imagery
from flight altitudes of 1,200 - 1,500 feet above the roof, so
high-resolution, large format IR cameras (See Figure 3) are required.
Figure 3) Large format infrared imager, fixed-mounted in a light
aircraft.
Once the aircraft is over a building, very little time
(five minutes per 200,000 square feet, about 25 minutes for two million
square feet) is required to fly over making multiple passes. The imagery
is recorded on digital videotape. Visual photographs are taken earlier
in the day or the next day. After returning to the office, the photos
are printed and the thermographs are saved on the computer. The raw
video imagery, thermographs and photographs are used to make an edited
videotape copy of the passes over the building. Both visual and infrared
images are used to do the analysis by overlaying the CAD drawing of the
roof 'over' the digitized photographs and thermographs. The drawings
always need to be corrected, because rooftop equipment has been removed,
moved or added since the last update of the drawings. Then, areas of
suspected moisture contamination are drawn on the CAD file. The result
is a report where visual, infrared and CAD components (printed and
video) are well matched and lined-up. The report is given to a roof
consultant who verifies the wet insulation during the day, while making
other condition notes on the roof.
Fixed-wing aerial infrared imaging provides many advantages over on-roof
infrared imaging:
·Access to multiple levels of the roof is not a problem. ·High-angle,
straight down infrared images lessen reflection problems.
·High-resolution images capture large areas at once, making report
writing easier and less expensive to produce. ·Plan-view imaging allows
for infrared images, visual images and AutoCAD drawings to be reconciled
closely. As a result, the report is clear, concise and easy to
understand (See Figure 4a, 4b, 4c). ·Plan view imaging allows accurate
marking of areas of suspect roof moisture contamination. ·The printed
CAD drawings can be used on the roof to paint areas of moisture
contamination directly on the roof (after verification), if desired.
Figure 4a) Photograph of a roof.
Figure 4b) Thermograph of a roof.
Figure 4c) Scaled CAD drawing of a roof.
The aerial infrared thermo-grapher can wait for a good
night for imaging, surveying many roofs under good conditions. ·The
trending of roof moisture becomes possible. ·An aircrew of two can
easily survey many millions of square feet in a single night.
·Processing the data is done in the office, not on the roof. ·Report
components can be purchased as needed. Aerial IR allows the building
owner to buy only the report he needs at that time.
The biggest advantage of aerial infrared is on roofs that are the most
difficult to image from any distance or angle. Roofs that, for instance,
have a lot of ballast, are covered with reflective coatings or for
whatever reason are impossible to image while standing on the roof. With
high-resolution, plan view aerial imagery, slight nuances of temperature
can be seen from far enough away to actually see the pattern of heat and
make a determination of where the problems are.
CONCLUSIONS
Every day millions of square feet of perfectly good roofing materials
are disposed of in our landfills. Why? Because roofs are often replaced
because know one knows where exactly the roof is damaged until it is too
late. If you want your roof to last, it must be regularly maintained by
professionals. Infrared roof moisture surveying is the best method of
non-destructive testing on roofs, and aerial infrared is the best
platform for performing infrared roof moisture surveys. Improvements in
IR cameras and flight methodology, aerial infrared thermo-graphy and
aerial infrared reports are getting better and more useable everyday.
About the Author
Author Biography Gregory R. Stockton is President of
Stockton Infrared Thermo-graphic Services, Inc.. (http://www.stocktoninfrared.com).
Greg has twenty-five years experience in the construction industry,
specializing in facilities construction, maintenance and energy-related
technologies. He has performed infrared thermo-graphy since 1989 and has
published fourteen white papers and numerous articles on infrared
thermo-graphy
