Maintenance World Article - Aerial
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 the extent of roof
moisture (water) that is inside the roof system. Infrared thermography 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, 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 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 thermographer
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 thermographer. 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 thermographer 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
thermographer 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 thermographer 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
thermography and aerial infrared reports are getting better and more useable
everyday.
Author Biography
Gregory R. Stockton is President of Stockton