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Building inspections have become more popular since Part
L of the latest building regulations recommended thermal
checks on new buildings for losses. HIPS inspections can
also involve Thermal Imaging.
Building Envelope
The primary diagnostic procedure for determining the
thermal performance of a building envelope is infrared
thermography. It can be used to identify heating and
cooling loss due to poor construction, missing or
inadequate insulation and moisture intrusion. Correcting
the defects plays a significant role in increasing
building efficiency and structural integrity.
Thermography can identify surface temperature variations
of the building envelope, which relates to problems in
the structure, thermal bridging, moisture content and
air leakage.
Two primary mechanisms for heat loss in buildings are
conduction through the walls and air leakage. Both can
be identified from the surface of the building with
infrared thermography. Early correction of the faults
identified can be made before extensive damage occurs.
Conductive Losses
Problems identified as conductive losses
include:
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Missing
insulation, improperly installed or compressed
insulation
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Shrinkage or settling of various insulating
materials
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Excessive thermal bridging in joints between
walls and the top and bottom plates
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Moisture damage to
insulation and building materials
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Heat loss through
multi-pane windows with a broken seal
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Leaks in water
pipes
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Damaged heat ducts
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Location of or leakage in buried steam lines, water
lines or underground sprinkler systems
Air Leakage
Air leakage is the passage of air through a building
envelope, wall, window, joint, etc. Leakage to the
interior is referred to as infiltration and leakage to
the exterior is referred to as exfiltration. Excessive
air movement significantly reduces the thermal integrity
and performance of the envelope and is, therefore, a
major contributor to energy consumption in a building.
In addition to energy loss caused by excessive air
leakage, it can cause condensation to form within and on
walls. This can create many problems; reduce insulation
R-value, permanently damage insulation, and seriously
degrade materials. It can rot wood, corrode metals,
stain brick or concrete surfaces, and in extreme cases
cause concrete to spall, bricks to separate, mortar to
crumble and sections of a wall to fall jeopardizing the
safety of occupants. It can corrode structural steel,
re-bar, and metal hangars and bolts with very serious
safety and maintenance issues. Moisture accumulation in
building materials can lead to the formation of mould
that may require extensive remediation.
Virtually anywhere in the building envelope where there
is a joint, junction or opening, there is potential for
air leakage. With the use of an infrared imager, one can
identify thermal irregularities on the building envelope
and the thermal pattern discerning whether the pattern
indicates a problem with the insulation, air leakage or
the building structure.
Infrared Inspection of Roofs
Flat roof membranes are the waterproof barriers between
the outside elements and the interior of buildings. They
come in a variety of materials and designs, and must be
able to expand and contract, resist high winds and the
effects of solar radiation and withstand foot traffic.
It is easy to see why roofs leak.
Normally there is little or no water within a flat roof
assembly. When a leak develops, water enters the
assembly and, depending on the type of insulation
system, is either absorbed by the insulation or runs to
the cracks between the non-absorbent insulation. When
water enters the roof assembly it is there for a long
time, sometimes the life of the roof.
Thermal capacitance is the physical property of a
material’s ability to store heat. The materials in roof
assemblies have relatively low thermal capacitance,
especially when compared to water. Water requires a lot
of energy to raise its temperature and likewise must
release a lot of energy to cool.
The physics used for thermal roof inspections is that
dry roof insulation heats up and cools down faster than
wet roof insulation. Infrared inspection goes beyond
simply finding a leak by locating the extent of the
moisture invasion of the insulation. To do this we
require solar heating of a sunny day. Then at night,
after the sun goes down and the roof surface begins to
cool, the dry roof insulation cools faster than wet roof
insulation.
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Was it a clear sunny day?
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Is it a clear night (for good radiation cooling)?
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Is there little or no wind?
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Is the roof surface dry?
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Is the roof clear of snow, dirt and debris?
The type of insulation used on a roof will result in an
infrared image that is characteristic of how that
particular insulation absorbs water. Absorbent roof
insulation acts similar to a sponge. The water migrates
by capillary action throughout a complete roof board
before it jumps to the adjacent board. This results in a
checker board thermal pattern.
Non-absorbent roof insulation creates a much different
pattern when it becomes wet. The water is not absorbed
and runs to the edge of the roof board. The water tends
to collect at the edges of the boards resulting in a
window frame pattern. Different patterns may result from
other less common insulating systems.
There are many conditions that can produce thermal
patterns that may look like they were created by wet
insulation but are not, and others may mask the true
condition of wet insulation. The ASTM specification
C-1153 titled “Location of Wet Insulation in Roofing
Systems Using Infrared Imaging” suggest performing
verification of suspected wet insulation by core
methods. The following are some examples of situations
that may result in poor infrared inspections:
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Insulation with different R-values or different
absorption characteristics which are commonly found
in repaired areas
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Different internal building temperatures
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Extra gravel or bituminous left from construction
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Warm or cold air exhausting onto roof
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Re-radiation of heat from south or west facing walls
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Wind
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Internal sources of heat or cold such as lights,
heaters, and steam pipes
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Dirt, vegetation and debris
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Walkway pads and buried steel plates
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Blisters
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Water ponding, steam plumes and water spray
During the winter thermographers use the same process, however, winter
surveys are more difficult because the temperature
differences are usually less than on summer surveys (5°F
vs. 20°F). If the building is heated, the added heat flow
from the building through wet insulation will help
enhance the winter thermal patterns.
Moisture Detection - A key to Prevention of Mould Growth
Mould has existed in our environment long before the
recent awareness of its presence in homes and
businesses. The impact of mould on health is dependent
upon the concentration of spores in the immediate area
and the allergic effect on an individual. Potential
health problems associated with mould exposure can take
the form of allergic reactions or asthma. The problem is
not limited to homes. Commercial buildings with moisture
accumulation due to condensation or leaks are a
candidate for mould growth.
According to the U.S. Environmental Protection Agency,
there is no practical way to eliminate mould spores in
an indoor environment. The best way to control mould
growth is to control moisture. Mould can begin growth in
as little as 24 hours. Roof leaks and water pipe leaks
are common sources of water accumulation that may cause
mould growth. Mould has closed public schools and caused
companies to spend millions of dollars on environmental
tests and remediation. Clearly, there is more reason to
become aware of roof conditions, before water begins
dripping on a building owner’s head.
Moisture present in roofs and walls can be detected with
a sensitive infrared camera under the right conditions.
Infrared roof inspections are performed most effectively
after sunset, when the roof gives off its heat energy
accumulated during the day. The heat capacity of
moisture soaked roof insulation is greater than that of
dry insulation. As a result, the moisture soaked roof
areas appear quite clearly when performing an infrared
scan.
Similarly, it is possible to detect moisture located
behind interior walls with an infrared camera, under the
right conditions. The temperature difference created by
the presence of moisture on the inside surface of a wall
will appear differently than the surrounding area.
Infrared inspection is a fast, non-invasive method to
discover moisture intrusion within the building
envelope. It does not directly detect
the presence of mould, rather it may be used to find
moisture where mould may develop. The limitations to
obtaining accurate infrared images pertain to the
ability of the surface being scanned to emit heat
energy. Gypsum (dry wall) in interior walls emits quite
well, whereas highly reflective surfaces do not. Since
the temperature difference between the wet and the dry
wall are very slight, a sensitive infrared camera must
be used.
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