Infrared Thermography for Roof Investigations

ABSTRACT
Infrared thermography is an excellent
investigative tool used for a multitude of
building-specific applications, including
roof investigations. Since its introduction
in the 1970s, lower prices and technology
advances have allowed thermography to
expand, becoming an indispensable tool for
roof investigators. For roofing applications,
thermography is typically used for condition
assessment and forensic studies of the
low-sloped roof. Since many papers have
been written on this subject, this article will
summarize the discussions on how infrared
thermography works as a tool for roof investigations.
1-6
INTRODUCTION
Infrared has been around long enough
that many professionals
use infrared analysis
for building applications,
including lowslope
roof inspections.
Before the use of infrared,
roofing professionals
had to go to great
lengths to detect leaks
caused by moisture
intrusion, though electrical
methods were
available for determining
roof leaks. The use
of infrared imagers in
detecting roof leaks
has provided the roofing
industry with a tool
that has become essential to low-slope roof
leak inspections.
In the past, time and resources were
used to carefully inspect all areas of the
roof, below and above, to determine if it was
leaking or to locate an intrusion site. For
the trained roof thermographer, now a roof
overview can be as simple as a quick flyover,
though onsite inspections are important to
confirm any flyover findings.7-9 For building
owners, advances in technology have made
infrared imagers one of the most costeffective
ways to detect and locate damaging
roof leaks and to provide corrective
measures.
In 1990, ASTM C1153, Standard
Practice for Locating Wet Insulation Using
Infrared Imaging, was published and is
still in use with very few changes today.10
Unfortunately, while imagers have improved
dramatically, the approaches to roof inspections
have not, as demonstrated by the
minor changes of the current version (i.e.,
2010) of ASTM C1153. One neglected aspect
of this standard is that it only describes
night investigations. It is clear from many
years of experience that the laws of physics
apply to day surveys as well.4
Understanding and using thermography
to detect a roof leak or wet insulation is
much more difficult than just pointing and
shooting a thermal imager. Experts need to
spend many months as active thermographers
and go through many hours of training
to achieve competency. In the hands of
a trained professional, though, roof leaks
can be detected in a variety of ways using
infrared thermography.
A u g u s t 2 0 1 3 I n t e r f a c e • 1 1
Figure 1 – Infrared radiation is emitted from the roof surface and detected by the infrared imager that converts
the invisible infrared to a visible image.
1 2 • I n t e r f a c e A u g u s t 2 0 1 3
HOW DOES IT “SEE” THE LEAK?
The roof emits infrared radiation,
according to the laws described by Planck,
Stefan-Boltzman, and Kirchhoff. An infrared
imager converts invisible infrared radiation
into a visible image by detecting the incoming
infrared electromagnetic energy and
intensities from the roof with its detector.
Just as in visual photography, the infrared
electromagnetic energy is focused with
a lens onto a detector, which then processes
the information into a visual image
displayed onto the viewfinder as shown in
Figure 1. The intensity of the radiation, coupled
with the
imager’s electronics,
can
yield thermal
patterns on
the surface of
the roof being
inspected.
IMPORTANT IMAGER
SPECIFICATIONS11
In order to capture and interpret the
thermal image, it may not be necessary to
fully understand how the imager’s internal
components work or the need to adjust
the parameters for correct temperatures.
However, when purchasing, it is important
to understand some of the basic specifications
of the infrared imager. The two most
important specifications are image resolution
and thermal sensitivity. Image resolution
is very important when observing the
roof from a distance, as when performing
a flyover or from an adjacent building, to
provide clear images to the client. Thermal
sensitivity is important when little temperature
variation is present and a higher
contrast is needed.
Most infrared imagers applicable for
roof inspections have an image resolution
of at least 320×240 (76,800 pixels or 0.07
megapixels), though lower resolution can
still provide the majority of details to resolve
moisture locations, provided one is close
enough. Unfortunately, 0.07 megapixels
is much less than the digital cameras we
use to visually document the inspection.
Higher resolutions are needed when greater
distances are are involved in observing the
roof, such as in a flyover. For this application,
to compensate for a lower-resolution
imager, a telephoto lens is sometimes used,
and images are stitched or merged together.
One way to increase resolution as well as
wider viewpoint is to stitch multiple images
together. In Figure 2, three images were
stitched together to show a wider viewpoint
and higher resolution as compared to the
single image shown in Figure 3.
For on-roof thermography, where close
distance observation is performed, some
thermographers use a wide-angle lens. This,
like stitching, increases viewing angle, facilitating
a larger instantaneous viewing area
of the roof surface. The wide-angle lens can
minimize the scan area and the need for
multiple images.
The thermal sensitivity or noiseequivalent
temperature difference (NETD)
for an infrared imager is measured in
degrees Celsius (°C) or milliKelvins (mK).
It is the measurement of the smallest temperature
difference that a thermal imager
can detect in the presence of electronic
noise. A 50-mK (0.05°C) sensitivity is two
times as sensitive as a 100-mK (0.1°C). The
NETD can be as important as resolution
when deciding what imager to purchase.
An experienced thermographer can usually
distinguish thermal images having as little
as a 10 mK NETD difference. The lower the
thermal sensitivity, the more detailed and
less noise present on the thermogram. This
is especially evident in the case when using
small thermal spans.
Highly sensitive
(low-NETD) thermal
imagers will show
more temperature
differences, and thus
more patterns.
The thermograms
in Figures 4
and 5 were taken
with the same infrared
imager but
tuned to different
temperature spans.
The thermogram in
Figure 4 has a span
of 3°F, which is narrower
than Figure 5,
with a span of 36°F.
Figure 4 is grainier
than Figure 5. If the
imager has 256 dis-
Figure 2 – Wider-angle, multiple-image view.
Figure 3 – Narrower, single-image view.
Figure 4 – A narrow, 3°F (1.7°C) span. Figure 5 – A wider, 36°F (20°C) span.
crete color levels,
then for the narrow
span in Figure
4, each color level
would represent
0.011°F or 0.006°C
(6 mK). This is far
more sensitive than
the 50-mK (0.05°C)
NETD specification
for this imager,
causing increased
noise in Figure 4.
The infrared
imager’s frame rate
or capture rate may
be an issue if the
stabilization of the
imager is difficult.
A low-frame rate
(9Hz) makes it difficult to stabilize or freeze
the image for capture. This is very important
if the imager is bouncing due to turbulence
during a flyover (especially helicopter
flights) or from a thermographer’s hands
after too many cups of coffee. A 30-Hz or
better frame rate should be considered—
especially for flyover applications.
Another imager specification for roof
investigation is detector wavelength. Midwave
detectors (3-5μm) can provide less
cold-sky reflection (Figure 18) than the longwave
band of 8-14 μm. More of the midwave
band is absorbed by the atmosphere
than the long-wave wavelengths of 8-14 μm.
This reduces the radiation from the cold
sky when using midwave imagers, resulting
in an attenuated component of the energy
reflected (originating from the sky) by the
roofing material. This is especially useful
for low-emissive roofing, such as reflective
roof coatings.
WHY DOES THE WET INSUL ATION
SHOW A PATTERN?
The thermal patterns observed on the
roof where wet insulation is present are due
to material differences in “thermal capacity”
or “heat capacity.” This is the amount of
heat (energy) required to raise a unit mass
one degree in temperature. The chart in
Figure 6 provides a graphic representation
of specific heat of various materials, from
gold to water. It is clear that water has the
highest heat capacity of the materials listed.
In fact, it has such a high-heat capacity that
it takes water almost ten times longer to
heat than steel. Once materials with a high
specific heat are heated, they stay warmer
longer or cool more slowly.
When it comes to roofing, the heat
capacities of various roofing materials have
at least half the heat capacity of water (1
Btu/lb. °F) as shown in Figure 7. In the
morning, when the sun heats the roofing
material, the water heats at a slower rate
(than the roofing material), conveying a
cooler thermal pattern for the trapped water
or wet insulation. As the sun sets, the
heat capacity of the water keeps the water
pattern warmer longer, providing a heated
thermal pattern for the wet insulation.
The thermographer can observe thermal
patterns both in the evening, just after
sunset; or in the morning, just as the sun is
A u g u s t 2 0 1 3 I n t e r f a c e • 1 3
Figure 6 – Heat capacity of various materials in Btu/lb. °F.
The RCI Foundations –
Supporting The Industry
RCI Foundation – United States
Web site: www.rcifoundation.org
E-mail: foundation@rci-online.org
RCI Foundation – Canada
Web site: www.rcifoundation.ca
E-mail: info@rcifoundation.ca
Figure 7 – Heat capacity of various roofing
materials in Btu/lb. °F.
rising, due to the
thermal capacity
differences of water
and roofing
material. The
temperature data
shown in Figure 8
indicate temperature
differences of
wet or dry insulation
during the day and evening.
ROOF INSPECTING
Walk-on inspections
may require a wideangle
lens or the stitching
of multiple images
to provide a wide angle
of view shown in Figure
9 as compared to the
standard lens shown
in Figures 10 and 11.
Additional thermal patterns
may be confused
for trapped moisture. The small hot spots in Figure 10 are due to the high conductivity
of the fasteners. Whenever there is a concern, moisture meter testing
(Figures 12-13) or nuclear radioisotopic thermalization12 (Figures 14-15)
should be used to confirm the patterning observed by infrared thermography.
If following the ASTM C1153 standard, coring must be performed to confirm
the results of
the thermography
inspection.
Whenever
possible, onroof
viewing
will benefit
from a widerangle
lens or
from a higher
vantage point,
such as an
adjacent roof
1 4 • I n t e r f a c e A u g u s t 2 0 1 3
Figure 8 – Graph showing the temperatures of wet insulation
(green points) and dry roof deck (red points).
Figure 10 – Thermogram of an on-roof viewing.
Figure 11
– Visual
image of
an on-roof
viewing.
Figure 13 – Visual image showing
frozen water and a roof capacitance
moisture meter (Tramex RWS moisture
meter roof and wall scanner).
Figure 9 – On-roof viewing of multiple
stitched images, showing a wide view.
Figure 12 –
Thermal pattern
visible outside of
the frozen puddle.
as shown in Figures 16 and 17, especially when roof access may be difficult
or unsafe. In addition, a bird’s-eye view provides the thermographer a much
better overview than walking on the surface. The same building observed in
the roof inspection shown in Figures 16 and 17 is observed in a flyover in
Figure 18. Roof flyovers provide opportunities to investigate difficult-to-access
roofing, as well as multiple roof systems, in minutes. More area is
observed in a single frame from the vantage point of an aircraft above;
however, image resolution is important as shown in the difficult-to-interpret
image of Figure 19.
Unfortunately, ASTM Standard C1153 does not provide guidance for
daytime roof thermography. But since the physics do not change, thermal
patterning can be observed during the day as well as the evening. The graph
in Figure 8 clearly shows that temperature differences appear throughout
the day, as well as in the evening. Day thermography may be more difficult
than evening thermography due to high daytime temperatures overwhelming
the cool patterns of the wet insulation with hot spots or shadowing, as
shown in Figures 20-21. The comparison of an evening inspection (Figure 18)
and morning inspection (Figures 16-17) of the same area shows the dramatic
temperature differences, in part due to solar insolation differences of day
and night, shadowing, and night radiation heat transfer.
EMISSIVITY AND ANGL E
Thermal inspections of low emissive surfaces are limited due to the
increase in reflection. This is also apparent for on-roof inspections due to
the low angle necessary to observe distant areas as shown in Figures 22 to
24. Based on the Lambert’s cosine law, the radiant intensity observed is
directly proportionate to the cosine of the angle (see Figure 25).
A u g u s t 2 0 1 3 I n t e r f a c e • 1 5
Figure 14 – Wet insulation visible as a cool thermal pattern. Figure 15 – Technician performing nuclear moisture testing.
Figure 16 – Viewing from an adjacent roof.
Figure 17 – Viewing from an adjacent roof.
Figure 18 –
Flyover of
area shown
in Figures 16
Figure 19 – Flyover using low-resolution imager digitally zoomed. and 17.
1 6 • I n t e r f a c e A u g u s t 2 0 1 3
Fronapfel, in his 2006 InfraMation article, determined
the emissivity of various building materials and
the changes that were induced by adjusting the observation
angle.13 For roofing membranes made of ethylene
propylene diene monomer (EPDM), the emissivity was
observed to change from 0.95 to 0.85 when viewed at a
75-degree angle. Care should be taken when observing
low-emissive roofing or roof coatings. The observed thermal patterning
may be due to reflections and not temperature differences of the
material.
Underdeck inspections can be problematic due to low-emissive
coatings such as radiant barriers, but direct view is usually more
of an issue since the
underdeck is typically
concealed from
view. When direct
observation can
be performed, the
underdeck results
can be dramatic, as
shown in Figure 26.
REPORTING
RESULTS
Roof replacement
can be very costly for
the building owner.
By locating a leak or
damaged area, the
cost of repair is considerably
less than
a new roof. Infrared
thermography can
easily locate and document
the leaks, providing
a clear map
to correct the issues
without replacement
of the whole roof
(see Figures 27-29).
In addition to the
savings of postponing
roof replacement,
Figure 20 – Cooler patterns may be due to shadowing.
Figure 21 – Thermal patterns from reflection and
shadows.
Figure 22 – Reflection due to high angle obscures the roof.
Figure 23 – Heat reflecting from the building.
Figure 24 – Reflection from water on the roof
surface due to angle and the spectral (smooth)
surface of the water.
energy costs will be reduced. Wet fiberglass
insulation is 14 times more conductive than
dry insulation. Locating the wet insulation
and replacing it will save heating and cooling
costs for the building. Because of these
effective cost-saving measures and ease of
mapping wet insulation, infrared imagers
are the best method available today to
locate a roof leak.
IMPORTANT CONSIDERATIONS
WHEN INSPECTING
The foremost consideration for a roof
investigation is safety for the personnel.
Climbing onto the roof presents a clear
safety hazard of falling. In my personal communications
with building investigators,
I’ve heard from many survivors falling from
ladders and through decayed roofing, many
becoming physically disabled due to the
falls. We all believe it will not happen to us,
but it is a reality for many. Below is a simple
(but not all-exclusive) list of important safety
considerations:
• Always use proper restraints and
proper safety equipment during
inspections.
• Always inspect the underside of the
American Hydrotech, Inc. 303 East Ohio | Chicago, IL 60611 | 800.877.6125 | www.hydrotechusa.com
© 2013 Monolithic Membrane 6125 is a registered trademark of American Hydrotech, Inc.
Monolithic Membrane 6125, the original rubberized
asphalt membrane, has been entrusted with keeping
high profile structures across the country and around
the globe watertight for 50 years. More than 2
billion square feet of membrane is still performing
today as it did the day it was installed.
50 YEARS OF PROVEN PERFORMANCE – MONOLITHIC MEMBRANE 6125®
RCI-50-Half-Horiztonal.indd 1 12/11/2012 5:15:41 PM
A u g u s t 2 0 1 3 I n t e r f a c e • 1 7
Figure 25 – Reflection due to high angle
obscures the patterns radiating from the
roof.14 Figure 26 – Thermal pattern visible at the underside of the deck.
The ASTM C1153 standard notes the
following very important environmental
parameters:
• No appreciable precipitation for the
previous 48 hours. Infrared cannot
see through water.
• No standing water.
• Wind less than 25 km/h (15 mph) to
prevent convective heat loss of the
thermal patterns.
• Direct sunshine on the roof during
the day.
• At least 18˚F (10˚C) between inside
and outside of the roof if there is
little sun.
Not all thermographers are competent to
perform roof inspections. Training is important
for all thermographers, with most U.S.
training organizations using the American
Society for Nondestructive Testing, Inc.
(ASNT) Recommended Practices ASNT SNTTC-
1A as a guide.15 Though this guide is
universally cited for training guidance and
useful at providing
qualification
levels and experience
requirements,
it tends
not to provide
enough guidance
for the complex,
specific thermography
applications
such as buildings
or roofing. Both
require extensive
background in
building sciences
and construction
to provide competence
for this application of thermography.
The Canadian National Master Specification
(NMS) is providing a new approach
to the complex certification requirements
for thermography by developing specifications
for electrical, mechanical, roofing, and
building envelope industries.16 Others are
working on international standards that
provide more guidance on application-specific
qualifications and certification requirements
for thermography. It is clear that
proper equipment, training, and experience
are important for competency in the application
of roof thermography.
SUMMARY
Infrared thermography is the conversion
of invisible infrared electromagnetic radiation
into a visible image. It is important
to understand image resolution and thermal
sensitivity in order to choose the right
imager for an application. Lens types, such
as wide-angle, normal, or telephoto, are
also considerations. The high-heat capacity
800-771-1711
www.roofhugger.com
Over 60 Million
Square Feet of
Roofs Installed
Metal
Re-Roofing
Solutions
BENEFITS TO
ROOF CONSULTANTS
 PRELIMINARY LOAD ESTIMATES
 AUTOCAD DETAILS
 BUDGET ESTIMATES
 PERFORMANCE TESTING
 FLORIDA PRODUCT APPROVALS
 COMPATIBLE WITH ANY NEW
PANEL
ROOF HUGGER®
Patent #5,367,848
Figures 28 and 29
– Thermal images
locate the wet
areas.
A u g u s t 2 0 1 3 I n t e r f a c e • 1 9
of water provides the means for observing
thermal patterning of trapped moisture
within the roof system.
ISO 6781:1983 (Thermal insulation –
Qualitative detection of thermal irregularities
in building envelopes – infrared method)
and the similar ASTM C1153 standard are
currently the only available standards, but
are outdated due to fast-paced technological
advances in thermal imagers. These
standards provide good guidance for the
roof thermographer but little guidance for
daytime thermography. New or updated
standards are needed, as it is clear that
proper equipment, training, and experience
are important for competency in the application
of roof thermography.
Locating wet insulation will save the
building owner the cost of a total roof
replacement. Energy savings are also
achieved by replacing the highly conductive
wet insulation, thereby saving on heating
and cooling costs. Because of these effective
cost-saving techniques, infrared imagers
are the best method available today to evaluate,
map, and locate roof leaks.
Major advantages of an infrared roof
moisture survey are:
• Locates water-damaged insulation
quickly and accurately
• Identifies small problems before they
become serious and more costly to
repair
• Eliminates unnecessary replacement
of good roof
• Documents problems before the
warranty expires
• Greatly extends the life of the roof
A roof moisture survey should be carried
out:
• Prior to acceptance of a new roof
system or during a building’s commissioning
process
• Before any existing warranties expire
• Before acquiring a new building
• Before roofing over existing roofing
• For planned maintenance purposes
REFERENCES
1. Kathryn Barker Knettel. “Thermographic
Anomalies in Roof Membranes:
Wet Insulation or False
Indications.” InfraMation Proceedings.
Volume 1. 2000.
2. Kathryn Barker Knettel. “Thermographics
Involving Rubber-Based
Cap-Sheet Membranes.” InfraMation
Proceedings. Volume 3. 2002.
3. Palani Subramanian. “An Application
of Infrared Thermography – Roofing
Survey.” InfraMation Proceedings.
Volume 6. 2005.
4. David Khudaverdian. “A Global
Strategy for Evaluating Building
Roof Performance and Diagnosing
Moisture Intrusion Into Roofing
Systems Using Infrared Thermography
and Other Diagnostic Tools.”
InfraMation Proceedings. Volume 8.
2007.
5. Antonio Colantonio and Scott Wood.
“Detection of Moisture Within
Building Enclosures by Interior and
Exterior Thermographic Inspections.”
InfraMation Proceedings. Volume 9.
2008.
2 0 • I n t e r f a c e A u g u s t 2 0 1 3
www.rci-online.org/document-competition.html
RCI 2014 DoCument CompetItIon
eaRn RCI DollaRs anD otheR InCentIves
The winners of the 2014 RCI Document Competition will receive a plaque and
recognition during the annual awards luncheon at the 29th RCI International
Convention and Trade Show, publicity of their winning projects in Interface,
and RCI Dollars. Prizes will be awarded to nine winners in three categories.
laRge pRojeCt | small pRojeCt | RepoRt
First-place winners ……… 1,000 RCI Dollars
Second-place winners ….. 500 RCI Dollars
Third-place winners …….. 200 RCI Dollars
RCI Dollars will be redeemable for any product or service provided by RCI or
the RCI Foundation. RCI Dollars are redeemable by the award winner or by
anyone specifically designated by the award winner. Use winnings for yourself
or to help a friend or colleague buy a reference book or attend a seminar.
Entry deadline: October 31, 2013
DownloaD YouR entY FoRm toDaY!
RCI, Inc. 800-828-1902
6. Ronald D. Lucier. “Daytime Infrared
Roof Inspections.” Interface. RCI,
Inc. August 2004.
7. Gregory Stockton. “Selected
Applications and Methodology for
Aerial Infrared Thermography.”
InfraMation Proceedings. Volume 2.
2001.
8. Gregory Stockton. “Advances in
Aerial IR Applications.” InfraMation
Proceedings. Volume 8. 2007.
9. Gregory Stockton. “Methodologies for
Finding, Analyzing, and Prioritizing
Moisture Problems in Roofing
Materials Using Infrared Thermal
Imaging.” IRINFO, 2013.
10. ASTM C-1153 [97 (2010)]. “Standard
Practice for the Location of Wet
Insulation in Roofing Systems Using
Infrared Imaging.” American Society
for Testing and Materials. www.
astm.org.
11. Electrophysics Resource Center:
Infrared Inspection White
Paper: “Understanding Infrared
Imager Thermal Image Quality.”
Electrophysics Infrared Inspection.
2009.
12. “Detection and Location of Latent
Moisture in Building Roofing
Systems by Nuclear Radioisotopic
Thermalization,” ANSI/SPRI/RCI
NT-1, July 20, 2012.
13. Edward Fronapfel. “Emissivity
Measurements of Common Construction
Materials.” InfraMation Proceedings.
Volume 7. 2006.
14. Alex Ryer. Light Measurement
Handbook. International Light Inc.
1998.
15. Sandy Sanor. “The Professional
Infrared Thermographer.” Infra-
Mation Proceedings. Volume 2. 2001.
16. Antonio Colantonio. “Specifying
Infrared Thermographic Services
for Large Buildings.” InfraMation
Proceedings. Volume 8. 2007.
A u g u s t 2 0 1 3 I n t e r f a c e • 2 1
Scott Wood, president of Scott Wood Associates, LLC, is an
Air Barrier Association of America (ABAA) auditor and a Level
III thermographer. Starting in 2003, he created building
science thermography classes that he has since taught to
thousands. He is a founding member and treasurer of the
International Association of Certified Thermographers (IACT);
company advisor for ēssess, inc.; an active voting member
for ASTM International C16 committee; and a member of
the National Association of Commercial Building Inspectors
and Thermographers (NACBI), National Institute of Building
Sciences (NIBS), and the Seattle Building Enclosure Council (SeaBEC).
Scott Wood
A provincial government inquiry into the deadly June 23, 2012, collapse of the Algo Centre Mall in Elliot Lake, ON, which killed two and
injured more than 20, began in March and is expected to conclude in September.
Robert Wood, principal owner and president of engineering firm M.R. Wright & Associates, Inc. (MRW), Sault St. Marie, wrote a report
based on a visual inspection of the mall, stating that the mall’s roof was sound only seven weeks before it collapsed. He has since been
charged under the Occupational Health and Safety Act with providing negligent advice that endangered workers. He faces up to a $25,000
fine and a year in jail.
Wood and Gregory Saunders, his engineering partner who signed off on Wood’s report, had previously had their engineering licenses
suspended for designing a bridge that did not meet code. Saunders had regained his license after remedial exams, but Wood had not.
Saunders gave testimony that the partners were aware of ongoing leaks, mold, and severe rusting of steel beams from a 2005 report by
their own firm. Even so, they wrote in their May 2012 inspection report (contracted by mall owner Robert Nazarian to obtain new mortgage
financing for the mall) that the “members” were “still structurally sound.”
A class-action lawsuit into the collapse is ongoing, as leaks, mold, and water damage had been reported at the mall since its construction
in the 1970s. At a press conference announcing the lawsuit, it was noted that some residents had placed bets on when the building would
collapse.
NORR, an architectural and engineering company, has produced a 142-page report commissioned by provincial police and released to
the public in March 2013. The report states that leaking occurred because an “intrinsically flawed” waterproofing system installed in 1980
failed from the start and prompted years of complaints. “The fact that the roof was allowed to leak for 32 years is perplexing,” the report
states. Two companies—Pinchin and M.R. Wright—issued reports attesting to the soundness of the structure during that time.
According to NOOR’s analysis, the collapse occurred when a weld between a support column and beam failed in two stages because of
corrosion caused by years of water and road-salt penetration (part of the roof was used as a parking deck). NORR also alleges that Coreslab,
the company that supplied the precast concrete for the roof deck; and John Kadlec, the structural engineer, misled the mall’s original owner
about the capabilities of the product. The substrength hollow-core slabs did not play a direct role in the collapse, but their deficiency later
thwarted proper waterproofing solutions, NOOR claimed.
—Compiled from CBC News, CTV News, and ENR reports
Inquiry Continues Into Elliot Lake Mall Collapse