RESNET: Interim Guidelines for Thermographic Inspections of Buildings

RESNET Interim Guidelines for Thermographic
Inspections of Buildings
September 29, 2010
Purpose
This standard provides guidance on the use of infrared thermography for the
inspection of low rise, three stories or less, wood or steel frame, residential and
light commercial buildings. The three-fold purpose of this standard is to
• Provide for the means by which those wishing to obtain a RESNET
advanced certification in infrared thermography will have a means to do
so.
• Provide inspection guidance in using infrared thermography for air
intrusion and insulation inspections.
• Provide a possible substitute for an insulation inspection on a new building
where viewing of the insulation installation was not accomplished before
the drywall was applied.
This Standard also includes information for:
1. Using an infrared imaging system to determine radiation differences
associated with surface temperature variations of a building enclosure,
2. Determining whether the areas being viewed meet the specifications in
this Standard and in the RESNET 2006 Mortgage Industry National Home
Energy Rating System Standards.
3. Documenting the type and extent of any observed anomalies,
4. Locating the primary areas needing further physical inspection,
5. Providing an indication of thermal insulation performance and continuity,
and
6. Indicating areas affected by air and convection when an infrared imaging
system is used in combination with blower door operation.

Relationship to Other Standards
This chapter complements the RESNET Mortgage Industry National Home
Energy Rating System Standards. The referenced International Standards found
below have been used as a normative guideline in establishing these RESNET
Standards:
• ASTM C 1060-90 (2003): Standard Practice for Thermographic Inspection
of Insulation Installations in Envelope Cavities of Frame Buildings.
• ASTM E 1186-03: Standard Practices for Air Leakage Site Detection in
Building Envelopes and Air Barrier Systems.
• ISO 6781: Thermal Insulation---Qualitative Detection of Thermal
Irregularities in Building Envelopes---Infrared Method.
• Canadian General Standards Board, Document 149-GP-2MP, Manual for
Thermographic Analysis of Building Enclosures.

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• British Standard: Thermal performance of buildings. Qualitative detection
of thermal irregularities in building envelopes. Infrared method.
ISO6781:1983 modified.
• Canadian National Master Specifications (NMS), Section 02 27 13,
Thermographic Assessment; Building Envelope

Relationship to State Law.
This Standard recognizes that federal or state laws take precedent over this
Standard.

Scope
These standards are RESNET requirements for inspecting a building enclosure
using an infrared imaging system to locate defective insulation installations,
framing issues, air leakage, moisture intrusion, or thermal bypasses.

Infrared Training Providers
The Infrared Training Provider must be a RESNET HERS Rater Provider or a
RESNET Training Provider in good standing and have a RESNET Infrared Rater
Trainer on staff or under annual contract. The IR Training Provider will ensure
three months experience either before or after the training and will review the first
three reports or examples of old reports to ensure compliance with Section 802.8
of the RESNET Standards. The Provider will also ensure compliance with all
CEUs (18 hours in a three year period) necessary to remain a RESNET trained
Building Science Thermographer. RESNET will provide electronic
confirmation/recognition upon completing the RESNET Building Science
Thermographer certification requirements.

Requirements for Accredited Infrared Training Providers

1. Duties and Responsibilities. In order to maintain their accreditation in
good standing, all Infrared Training Providers shall fully discharge the
following duties and responsibilities. Failure to properly discharge all of
these duties and responsibilities shall constitute grounds for disciplinary
action in accordance with Chapter Nine of this Standard.
2. Keep confidential the test questions supplied for testing by the Infrared
Committee in the strictest confidence.
3. Any person or organization applying to be an Infrared Training Provider
must initially be a RESNET HERS Rater Provider or a RESNET Trainer
Provider.
4. Maintain for a period of three years all training materials and trainee data
including training schedules and curricula, attendance records
examinations and individual exam results, certifications, training manuals
and handouts, copies of current policies, standards, guidelines and
procedures in use by the Training Provider.
5. Maintain certified infrared trainers, either employees or contractors, who
satisfy the minimum trainer competencies in accordance with Section 802

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of these Standards. Each Infrared Training Provider must have a written
contract with the Infrared Trainer with starting and ending dates signed by
both the Infrared Trainer and the Infrared Training Provider.
6. Shall have the same Privileges and Rights as listed in Section 204.1.2
above.
7. The Infrared Training Provider will notify RESNET within 90 days as to any
change in status of the Infrared Trainer (employee/contractor).

Infrared Trainers
Those who wish to be trainers must be a RESNET Rater Trainer with a minimum
of Level II infrared training and certification. Each Infrared Trainer will be
required to complete the same number of CEUs as a RESNET Rater Trainer as
determined by RESNET in addition to a yearly webinar or session at the
RESNET conference concerning infrared. The RESNET IR Committee will
provide all test questions. The Infrared Trainers are to administer the IR test to
the trainees.. The test over the classroom material can be challenged without
taking any of the required classes.

1 Certification for Infrared Inspections of Buildings

All individuals applying for IR certification must have attained the RESNET
certification of at least a Building Performance Auditor (BPA). The person
applying to RESNET for the Infrared Inspection of Buildings Certification will have
two possible courses of action:

Method 1
1. The candidate must have a minimum of Building Performance Auditor
(BPA) certification and should be able to demonstrate sufficient building
science knowledge and understanding of the effects of stored heat, stack
and wind effect, solar heating, reflectivity, emissivity, material saturation
and surface moisture.
2. AND, the candidate must complete a course of study that fully complies
with the Level I Guidelines of the American Society for Nondestructive
Testing (ASNT). The course of study must meet the minimum ASNT
Guidelines of thirty-two (32) classroom hours and successful completion of
an exam. The exam will be in three (3) parts – general (written),
application specific (written), and practical (hands-on). Those who have
received their training outside RESNET must submit three thermography
reports following these guidelines for review by the RESNET Infrared
Certification Committee.
3. AND, should the RESNET Infrared Certification Committee require further
documentation of knowledge and abilities, the candidate must provide
either through written or video means, evidence of the ability to
performance of the following: a thorough knowledge of the operation of
your particular infrared imaging system, the ability to interpret
thermographs and other data, and the ability to confirm that test conditions

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are within set limits and are consistent with assumptions that support the
interpretation.
4. The RESNET Infrared Certification Committee will provide a certification
number to the individual once all criteria has been achieved.Certificates
will be issued after submittal of documentation showing 3 months of infield
experience.

Method 2
Without the training as indicated in Method 1 above, four courses of action must
be met to obtain a certification through RESNET:
1. The candidate must have a minimum of a Building Performance Auditor
(BPA) certification and should be able to demonstrate sufficient building
science knowledge and understanding of the effects of stored heat, stack
and wind effect, solar heating, reflectivity, emissivity, material saturation
and surface moisture.
2. A RESNET APPROVED IR training course with designated field and
classroom course work equaling 24 hours, which will require all topics of
study noted in Appendix F “Required Topics of Training and Weighting per
Section for 3-day RESNET IR certification training”. The required 24
hours of thermography training will include the following: a minimum of 16
hours in a classroom or an electronic setting; a minimum of 4 hours using
an imaging system in the field in the presence of a trainer; and a RESNET
standardized field test on the use of infrared imaging systems.”The infield
training must ensure that each individual fulfills all the requirements of
training specified in the curriculum for the course. Each student must
complete a thermography test of 50 questions administered by the IR
Trainer. The final part of the training is the submission of three
thermography reports that conform to currently accepted professional
guidelines and demonstrate the use a blower door in conjunction with the
infrared imaging system for review by the RESNET Infrared Certification
Committee. The three reports may be from actual inspections or can be
from the inspection of any available homes. Candidates will have a one
year period to submit the thermography reports.
3. The candidate must submit documentation of steps 1 and 2 above to the
RESNET Infrared Certification Committee and must provide to the
Committee upon request, further documentation through written or video
means of the following knowledge and abilities: a thorough knowledge of
the operation of his/her particular infrared imaging system, the ability to
interpret thermographs and other data, and the ability to confirm that test
conditions are within set limits and are consistent with assumptions that
support the interpretation.
4. The RESNET Infrared Certification Committee will provide a certification
number to the individual once all criteria have been achieved. Certificates
will be issued after submittal of documentation showing 3 months of infield
experience.

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Once all requirements have been completed, the RESNET Building Science
Thermographer will have the option to register with RESNET.. Registering with
RESNET will allow for the listing of the Building Science Thermographer’s name
on the RESNET website.

2 Thermographic Imaging Requirements

Infrared Imaging System Performance
The infrared imaging system must have the gain or contrast set so as to be able
to distinguish a framing member from the other parts of the envelope cavities
under the prevailing thermal conditions with the IR imaging system at a distance,
which permits the recognition of thermal anomalies. The imaging system should
be able to ensure any defects or anomalies won’t appear in either saturation
(maximum brightness or white) or in suppression (minimum brightness or black)
on the display or on the thermographic images. Some imaging systems that
meet the specifications may have fixed focus and automatic level and span
adjustment. It is the responsibility of the thermographer to adjust their viewing
position relative to the envelope surfaces to ensure that data is of acceptable
quality and the image is properly documented. This requirement assumes all
conditions for the inspection have been met. A radiometric camera is
recommended but not required. (Note: If temperatures are being measured, you
must also have the ability to adjust emissivity and set background reflected
temperature; this can be done in the camera OR by using software.)

Resolution
The Noise Equivalent Temperature Difference (NETD), which is a measurement
of thermal resolution or sensitivity, must be less than or equal to 0.10°C at 30°C
(0.18°F at 86°F).

Spectral Range
The infrared imaging system must have an operating spectral range that falls
anywhere between 2 and 15 micrometers (μm).

Field of View (FOV)
This is defined as the picture size or total field of view, which is normally
expressed in angular degrees or radians per side if rectangular and angular
degrees or radians if circular. The FOV should be capable of showing at least
two wall-framing cavities across while still being able to resolve an individual
framing member. In order to accomplish this prerequisite, a FOV of
approximately 20 degrees is suggested.

Recorded Images
The imaging system must have a means of recording images seen on the
camera’s screen. The images may either be in a video format or in individual still
frame images.

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Instantaneous Field of View and Detector
The detector and lens combination of the infrared imaging system must have
sufficient resolution to resolve framing members and the small void areas or wall
cavities. For practical purposes, the camera’s detector array must have no less
than 120 x 120 pixels.

3 General Inspection and Thermography Requirements

Observe the following general requirements for any infrared investigation of a
building:
1. Sample thermal images must be taken of representative parts of the
building being investigated that demonstrate the majority of areas with
anomalies or defects. In addition, parts of the building having no
anomalies must also have a sampling of thermal images, which
demonstrate the correct functioning of building components.
2. Remove furniture, pictures, and other obstructions as necessary to gain a
clear field of view if necessary. This process is best accomplished by the
building owner or occupant up to 12 hours before the beginning of the
inspection. If items blocking a view of a building section have not or
cannot be removed, this fact should be noted in the report.
3. Note any anomalies on a drawing or catalog them with a visible light
picture for locating the defect for correction. Confirmation of the anomaly
using the means stated in #7 below is recommended prior to inclusion in
any report, as false positives are not uncommon.
4. Obtain your thermal images as close to perpendicular to the surfaces
you’re investigating as possible.
5. Change your position and view the same area a second time in areas
where there is the possibility of reflected radiation. Document area and
location of surfaces obscured by mirrors, metal, reflective tile or other low
emissivity coverings that affect interpretation.
6. The minimum criterion for satisfactory thermal conditions is the ability to
distinguish the framing materials from the wall cavities. An inside to
outside temperature difference of the wall surfaces of at least 10°C / 18°F
for a period of 4 hours is recommended. (Ref: ISO 6781, 5.1, a.
recommends 10°C for a period of 24 hours. Therefore the instruments
controls must be set to show framing details clearly. If framing images
can’t be resolved, and inspection conditions can’t be altered artificially,
then reschedule the inspection for a time when temperature difference
conditions are achieved. If the temperature is within range and no studs
are visible, confirm the presence of continuous foam insulation or atypical
framing in the wall assembly before aborting the test. Document the
conditions and complete sections of the house that scan “normally”. False
negatives are possible with details that have reduced thermal bridges; for
example, flat roof sections with all the insulation above the deck may not
show framing issues.
7. Investigate any anomalies through the use of

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• Physical examination of the building details at “best” and “worst” or
other representative locations to calibrate the range of variation under
these specific conditions,
• Other means of investigations (e.g. moisture meters, surface
temperature devices, air exhaust devices),
• Experience, or
• By comparing to thermal images of normal building surfaces or with
reference thermographs of known defects.
8. Exterior examination of a building
a. Verify that no direct solar radiation has heated the surfaces to be
examined for a period of approximately 3 hours for frame construction
and for approximately 8 hours for masonry veneer construction.
b. Plan exterior investigations for an appropriate time after sunset, before
sunrise, or on an overcast day when the influence of solar radiation
can be determined to be minimal.
c. Verify that wind speed is less than 8 mph.
d. Verify the exterior surfaces are dry.
e. Check and record that the ongoing test parameters, such as the
temperature difference (∆T) across the building enclosure, wind speed,
and inside pressure with respect to outside pressure during the
inspection remain close to original readings since significant variation
may skew the outcome of the tests.
9. Interior investigations can also be influenced by wind, sun, sky condition
and moist exterior surfaces. These influences typically lag the more direct
exterior influence by 2-6 hours depending on conditions and structure
type. Some of the conditions you may encounter are as follows.
a. Interior partitions between rooms at different temperatures may appear
abnormal and provide false positive images if not confirmed (a thermal
bypass to a buffer space or to outside).
b. Stored items, cabinets, bathroom fixtures and reflective finishes may
limit wall scan to sample areas. Where possible, scan obscured
surfaces from the opposite side.
c. Buffer zones such as attics, crawlspaces, basements, attached
garages may hold air at a temperature different from interior and
exterior.
d. Chases and interior surface coverings open to the exterior or between
buffer zones such as dropped soffits, plumbing walls, plumbing wall
edges, floor joists open to porch roofs may show extensive IR contrast
under wind or blower door operation, but appear without defect under
as found conditions.
e. Ductwork, plumbing, electrical lines, and radiant heating components
built into soffits, ceilings and floors may appear as anomalies but also
obscure details of the construction assembly that holds them.
f. Additional interior cavities such as furring spaces behind interior finish
materials found in back-plaster and some remodeling can obscure the

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conditions in the main building cavity. This construction detail can
provide either false negatives or false positives if not confirmed.
g. Interior scans of hollow spaces such as interior cavities of Concrete
Masonry Unit (CMU) walls below grade and between units can show
convective loops where insulation is not continuous over the entire
surface. This should be documented.
h. Listed high performance windows sometimes fail and lose gas fill,
which can show up as anomalies in the glass away from the frame.
Repeat the scan at night and check surface temperatures if possible.
Drapes, curtains, and solar heating obscure viewing this effect.

4 Insulation Inspection

4.1 Procedures for Infrared Insulation Inspections

1. Qualitative analysis of installed insulation. Inspection used for
determining general areas of the inspected surfaces having anomalies
without quantification.
a. The ∆T between the inside and outside wall surfaces and as
defined by the surface being imaged must be a minimum of 10°C /
18°F or greater for a period of 4 hours before the inspection. If the
minimum ∆T is not present for this type of inspection, the inspection
must be rescheduled for a time when the ∆T is present.
b. If the inspection is done in conjunction with a blower door used to
depressurize the building to highlight any thermal bypasses, the
inspection can be performed with a minimum ∆T of 6.7°C / 12°F,
but an initial thermal survey of the inspection areas must be done in
order to verify changes in any areas where a thermal bypass is
occurring. Changes in anomalies must be explained in the report.
See Section 802.5 for complete explanation of air leakage
inspections.
2. Quantitative analysis of installed insulation for the purpose of grading
the insulation installation. Quantitative for this infrared investigation is
defined as determining the total square footage of anomalies of
installed insulation of a structure as a percentage of the total surface
area of installed insulation in the structure in square feet.
a. There must be a minimum ∆T across the building envelope wall
surfaces of 10°C / 18°F or greater for a period of 4 hours before the
inspection. The use of a blower door or any air exhausting device
is not allowed during or two hours before this specific insulation
inspection procedure. For quantitative grading of insulation, the
above stated minimum temperature difference at the time of the
inspection must be achieved. Otherwise grading of the insulation
cannot be achieved using this standard.
b. Recognized anomalies may be used to grade the insulation by the
guidelines in the 2006 Mortgage Industry National HERS

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Accreditation Standards (Appendix A “Sample Report”, pp. A-11
through A-16).
c. An insulation inspection demonstrating more than 5% anomalies
must be followed either by physical inspections to determine
whether there is missing insulation that must be documented or
modeled as uninsulated wall cavities.
d. Under these specified testing parameters, the IR imaging system
can also be used to locate thermal bridging areas. Thermal
bridging is defined as heat conduction through building
components, typically framing, that are more conductive than the
insulated envelope.
e. If the RESNET Rating Provider for the HERS Rater allows for a
more stringent inspection protocol for insulation inspections, then
this Infrared Standard should be used as a referenced Standard for
performing an infrared evaluation of onsite installed insulation. This
Infrared Standard may therefore be used for the grading of
insulation in any home in which a visual inspection of the insulation
was not conducted.

4.2 Insulation Grading Standards

Grade I
Grade I insulation installation cannot be verified using this infrared standard.

Grade II

Grade II must be insulation installed with anomalies found to be between ½%
and 2% for all inspected walls, floors and ceilings of the building.

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Grade III

Grade III must be an insulation installation having between 2% and 5%
anomalies found for all inspected walls, ceilings and floors of the building
enclosure.

4.3 Quantitative Grading of Wall Insulation

For determining the percentage of insulation anomalies, the inspector must use
the following method to comply with the quantitative insulation inspection.

Method for converting infrared insulation inspection to grading: Measure the
walls, ceilings, and framed floors to be inspected to the nearest square foot or
scaled from the building blueprints. Measure each insulation anomaly to the
nearest inch (see examples in Appendix C “Method for Converting Anomalies to
Insulation Grading”. Then divide the total square footage of the insulation
problem areas by the total square footage of the inspected surfaces.
1. Example: A building having 3100 square feet of inspected surfaces
(insulated walls, floors, and ceilings) and 50 square feet of anomalies
would have 1.61% of problem areas and therefore be considered Grade II.
2. Appendix B “Inspection Form for Thermal Bridging and Thermal Bypass
Investigations” contains examples of this method.

2.5 Air Leakage Inspection

The following procedures provide the thermographer with techniques for
inspecting the air barrier systems of a structure. These procedures are for
locating air leakage and thermal bypass sites (qualitative) and not set up to
determine quantitative airflow rates. A thermal bypass is defined as air
movement, air leakage or convection “cell”, that circumvents the thermal barrier,
is usually hidden, and is the result of an incomplete or compromised air barrier.
IR is an important tool for quickly finding the highest impact air leakage locations
in existing buildings. Documenting construction details where a change in IR

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image before blower door operation to during blower door operation is an
important component of the basic skill set of a building diagnostic technician.
1. The Air Leakage thermal inspection requires a temperature difference
between the inside and the outside of the building to be a minimum of
1.7°C / 3°F. This temperature difference will allow for surveying of
building surfaces to find air leakage sites and the temperature difference
must be maintained during the entire inspection.
2. Buffer zone air temperature is more important for this test. Attic air can be
at a higher temperature than interior air and very clearly show location and
severity of any existing bypasses when the IR scan is done before and
during blower door operation. Similarly, in weather with a 10°C/18°F or
greater inside/outside wall surface temperature difference, attic air can be
the same as interior air; then all the potential bypasses disappear from the
scan when the blower door is operated. In some homes both effects can
occur with separate attics or with slow scanning procedures as solar
heated attic air is replaced by cooler outside air. Brick finger space air
temperatures can reach over 100°F on the sunny side, which can aid in
determining wall details and floor joist connections on that side, but
obscure results on the shaded sides. Large openings inside joist and
partition wall volumes to adjacent buildings/units at the same temperature
will not be visible – these may dominate blower door leakage numbers
and provide odor and smoke transfer risk without a temperature signal.
3. Because air leakage sites may be difficult to locate under natural
conditions, air must be artificially forced across the building enclosure by
use of a fan such as a blower door or by using the mechanical and/or
ventilation system(s) in the building. Building depressurization and inside
inspection are preferred because of less interference of solar radiation and
wind. The outside air is at a different temperature than the inside air and
will therefore leave a thermal signature for the infrared imaging system to
capture. The largest volumes that change the fastest correlate with the
biggest gaps. Confirm the physical details of the largest framing volumes
at the edge that changes the most.
4. The thermal image for air leakage will appear as “fingers” or “streaking”
showing as dark when cold air is observed and lighter colors when warm
air is viewed. The thermal images will produce irregular shapes with
uneven boundaries and large temperature variations. These air leakage
sites are often at joints, junctions or penetrations in the enclosure. There
is often a temperature gradient within a finger or streaking area. An
isotherm function on the camera or color display can isolate the highest
contrast portion of each anomaly, which is typically closer to the source or
construction defect. Note, any interior insulation, surface coverings, or
additional cavities (such as behind paneling) may mask the full path. A
scan of all interior surfaces may reveal indications of significant air
leakage in locations not imagined as connected to the exterior.
5. Depressurization is employed for an interior inspection and pressurization
is utilized for an exterior or attic inspection.

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a. When depressurizing the building, the resultant air leakage should
be allowed to alter the building’s surface temperatures for a
minimum period of 10 minutes, depending on outside air
temperature. It is recommended that pressures on the building
envelope of 20 Pascals be reduced to less than 10-15 Pascals after
30 minutes if leakage locations are to be labeled in order of
importance.
b. As much as possible view all the key details at the same time. The
interior finish will cool and show more contrast over time so details
seen later appear in greater contrast. But pressurization or
depressurization, when there are extreme temperatures outside,
can also result in a change to the interior temperature of the
building and consequent loss of conditions over time for adequate
and reliable imaging by equalizing the Delta T.
c. Construction detail knowledge of the investigated structure is more
important than the actual surface temperature change. The airflow
required to slightly cool (0.2°C) 30 lineal feet of 2x10 ceiling joist
above a first story room that is open to a porch roof is hundreds of
times greater than the amount of air required to get a 1/4” wide 3”
long high contrast finger of air infiltration from an outlet or attic
access weather strip corner. Cooling or heating an entire joist
cavity between floors with air infiltration will take longer than finding
an air leak around an electrical box.
d. For the procedure, normal pressure differences across the building
envelope must be between 10 and 20 Pascals. The higher
pressure readings intensify surface temperature differences and
further aid in the discovery of air leakage sites.
e. Pressure readings must be taken separately on both the leeward
and windward side of the building and whenever possible in the
same areas on each floor of a multi-story building.
6. When depressurizing a structure, turn off or switch to pilot any combustion
appliances in the conditioned space. Close fireplace dampers and cover
ashes to prevent ashes from becoming airborne.
7. Although the primary air leakage sites viewed will be at the building
enclosure, interior walls and floor/ceiling cavities must also be viewed
since air leakage from the attic and basement are also a possibility.
8. Take care to discriminate between thermal bridging sites and thermal
bypass or air leakage sites. Thermal bridging sites will not change size or
shape during the inspection.

2.6 Inspection for Thermal Bypass and Thermal Bridging

1. Delta T requirements must be met for each specific anomaly being
investigated, whether it be insulation (a minimum of 10° C/18° F or
greater) or air leakage (a minimum of 1.7°C/3°F) situation. Thermal
bridging (as defined in Section 802.4.1, 2d) is part of the insulation

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inspection and thermal bypass (defined in Section 802.5) is a component
of the air leakage testing.
2. One of the problem situations for which the building is being examined
through the use of infrared is to identify areas of the walls where
excessive framing materials have been installed and therefore a larger
framing fraction should be used in analysis of that portion of the wall,
lowering the net R-value.
3. The second area of investigation in this area has to do with the
introduction of unconditioned air either around installed insulation or within
an interior wall cavity or interior space of the house. When a blower door
is used (see section 805.1, Qualitative Analysis, #2) for the purpose of
enhancing any apparent thermal bypasses, an initial thermal survey of all
suspect areas must be performed first to establish a baseline view of any
encountered anomalies. The blower door must then be turned on and
allowed to run for ten minutes. The anomalies must then be viewed a
second time with the infrared imaging system and any changes
documented visually and by location.
4. If the RESNET Rating Provider for the HERS Rater allows for a more
stringent inspection protocol for thermal bypass and thermal bridging
inspections, then this Infrared Standard should be used as a referenced
Standard for performing an infrared evaluation of onsite thermal bypasses
(air intrusion) and thermal bridging (insulation) as found in Sections 802.4
and 802.5. This Infrared Standard, with the associated requirements for
thermal imaging, may therefore be used for the evaluation of the presence
of thermal bypasses and thermal bridging in any home in which a visual
inspection for these thermal bypasses and thermal bridging was not
accomplished.
5. A sample report can be found in Appendix B“ Inspection Form for
Thermal Bridging and Thermal Bypass Investigations”.

2.7 THERMOGRAPH INTERPRETATION

The following guidelines are to help you in the interpretation of thermal images.
1. As the thermographer, you should routinely select a familiar display
palette for ease of identifying hot and cold areas. A gray scale or
monochromatic color palette is generally recommended for on site use
because of the ease of interpretation of the images seen.
2. Typical building investigations of insulation, air leakage, framing, moisture
intrusion and thermal bypasses do not require the identification of specific
temperatures. These readings may be informative, however, when
comparing actual surface wall or ceiling temperatures with the thermostat
set point.
3. You must be aware of specific emissivity values of materials or
components being viewed in order to identify reflected radiation. Moving
to a different location while viewing a surface will help identify reflected
radiation.

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4. Secondary methods of verifying anomalies may include experience, onsite
measurements with specific devices (e.g. a moisture meter), or by
comparison to reference thermal images from houses with known
anomalies or without anomalies.
5. The basic determining factor for correct interpretation is if the temperature
distribution differs from that expected for the type of construction being
viewed with the infrared imaging system. If the apparent anomaly can’t be
explained by the design of the building envelope, effects of heat sources,
variations of emissivity, or by the physics of heat transfer, then the
anomaly may require further investigation.

2.8 REPORTS

Reports must be generated for each specific type of investigation whether
insulation, air leakage, framing, or thermal bypass. All of the following elements
must be part of each report. A sample report can be found in Appendix
A”Sample Report”.
1. A brief description of the way the building has been constructed.
2. Types of interior and exterior surface materials used in the building.
3. The geographical orientation of the building with a description of the
exterior surroundings including other buildings, vegetation, landscaping,
and surface water drainage.
4. Camera brand, model and serial number.
5. The name of thermographers and inspectors present.
6. Date and hour of tests.
7. Inside air temperature(s).
8. Ambient (outdoor) air temperature.
9. Temperatures of buffer zones and attics.
10. Indoor and outdoor relative humidity.
11. General information for the last 12 hours on the solar radiation conditions
in the geographic area where the test is being performed.
12. Ambient conditions such as precipitation and wind direction and speed
occurring within the last 24 hours, as applicable. Refer to specific
requirements in each section of each inspection type for requirements in
each specific area.
13. Records of the portions of the building, which were not within, test
conditions when the scan was performed and which portions were
obstructed by adjacent structures, interior cabinets, intervening cavities or
reflective surfaces.
14. Other relevant information, which may have influenced the test results.
15. Drawings, sketches and/or photographs detailing the locations in the
building where thermograms were taken detailing possible irregularities in
the components being tested.
16. Thermal images taken during the inspection with their relative locations
and written or voice recorded explanations of the anomaly listed along
with visual and reference images. Any spot, line or area temperature

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measurement marker embedded in a thermal image shall also include
information regarding its spot, line or area emissivity and background
temperature setting.
17. An identification of the aspects or components of the building being
examined.
18. Include the results of the analysis that explains the type and the extent of
each construction defect observed during the inspection.
19. Any results from additional measurements and investigations. Identify
additional equipment used and support with type, model number, serial
number, and any calibration that has been performed on the devices.

2.9 SAFETY CONCERNS

It is not the intent of this standard to address safety concerns, if any, that may be
associated with its use. It is the sole responsibility of the thermographer or user
of this document to provide personal protective equipment, to follow any
applicable manufacturer’s guidelines for the operation of all diagnostic
equipment, and to be familiar with health and safety practices or regulations for
those involved with any of the previous procedures described in this document.
The thermographer is held accountable for all company, local, state, and federal
regulations regarding the various aspects of these inspections and their possible
application to the work site.

2.10 DEFINITIONS AND ACRONYMS

Abnormal: Some defect exists in the construction and operation of the building
enclosure.

Air barrier: Any solid material installed to control air leakage either into or out of
the building envelope.

Air exfiltration: Air from the conditioned space leaking outside of the thermal
boundary of a structure.

Air infiltration: Air from outside the thermal boundary of a structure, which
enters the conditioned space.
Air leakage site: A specific location in a structure where the air barrier has
irregularities in it allowing both air infiltration and exfiltration depending on the
interior pressures of the building.

Air wash: The movement of air through insulation.

Anomaly (defect): An area of a building where the temperature distribution
seen with an infrared imaging system differs by more than 4°F from the
temperature distribution expected for the type of construction being viewed,
denoting a possible problem area; an inconsistency.

Page 15 of 32

ANSI: American National Standards Institute

ASNT: American Society for Nondestructive Testing

ASTM: ASTM International, originally known as the American Society for
Testing and Materials (ASTM)

Blackbody: An object or surface which absorbs all radiant energy, within a
specific spectral band, coming into contact with the surface and does not reflect
or transmit any. Thus, the surface has an emissivity of 1.

Building envelope: The components of a building (walls, ceilings, windows,
doors, floors, and foundations) that separate the conditioned space from the
unconditioned spaces or conditioned space from outside..

Compression (insulation): This condition includes but is not limited to batt
insulation compressed behind plumbing, heat and air, electrical, and other in
cavity obstructions that results in the loss of R-value of the installed insulation.
This condition can also occur within a wall cavity without obstructions. See also
“Misalignment”.

Defect: See Anomaly

Emissivity: The ability of a surface to emit radiation, measured as the ratio of
the energy radiated within a specific spectral band by a surface to that radiated
within that same specific spectral band by a blackbody at the same temperature.

Field-of-view (FOV): The total area of height by width, normally expressed in
either degrees or radians, in which an infrared imaging system is capable of
displaying, imaging, and recording objects.

Framing spacing: The distance from center to center of wall studs, ceiling
joists, floor joists and roof rafters.

Gaps (insulation): An insulation defect where installed insulation does not
completely fill areas of the building enclosure, which allows for conductive and
convective heat loss and a reduced R-value of the overall building enclosure.

Infrared imaging system: An instrument that converts radiation differences
associated with surface temperature variations into a two dimensional image by
assigning specific colors or tones to the differing temperatures.

Infrared thermography: The process of using an infrared imaging system to
generate thermal images of the surfaces of objects, which can be viewed
electronically or printed.

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“Infrared Training Provider – A firm or organization, who is currently qualified
as a RESNET HERS Rater Provider or a RESNET Training Provider, that
develops, manages, and operates an infrared training and quality assurance
program.”
Instantaneous Field of View (IFOV): The instantaneous spatial resolutions
characteristics of infrared imagers (expressed in angular degrees or radians per
side if rectangular and if round, in angular degrees or radians), or the smallest
object able to be viewed by the imaging system at a given distance.

ISO: International Organization for Standardization.

Level I Thermographer: A person who is qualified by training, experience and
testing to gather high-quality data and, where pass/fail guidance is provided, to
interpret that data. The American Society for Nondestructive Testing (ASNT)
defines a Level I as one who can
• Perform calibrations, tests, and evaluations for determining the
acceptance or rejection of tested items in accordance with specific written
instructions.
• Record test results but have no authority to sign reports for the purpose of
signifying satisfactory completion of NDT operations.
• Receive instructions or supervision from a Level III or designee.

Misalignment (insulation): This defect occurs when installed insulation is not in
contact with the air barrier and air intrusion between the insulation and the air
barrier seriously compromises the effectiveness of the insulation in framed
buildings.

Normal: The building shell is functioning as designed.

Qualitative: In relation to insulation inspections, determining general areas of
anomalies without assigning temperature values to the patterns.

Quantitative: In relation to insulation inspections, determining the total square
footage of anomalies of a structure as a percentage of the total surface area of
the structure in square feet.

Spectral Wavelength: The electromagnetic wavelength interval or equivalent
over which observations are made when using an infrared imaging system.

Thermal boundary: The line or boundary where the air barrier and insulation
are installed in a building assembly. The air barrier and insulation should be
adjacent to one another in a building assembly to prevent airflow from
circumventing insulation.

Page 17 of 32

Thermal bridging: Heat conduction through building components, typically
framing, that are more conductive than the insulated envelope.

Thermal bypass: Air movement, air leakage or convection “cell”, that
circumvents the thermal barrier, is usually hidden and is the result of an
incomplete or compromised air barrier.

Thermal image: A recorded electronic or printed image provided by an infrared
imaging system of the thermal surface variations of an object or a surface.

Thermal resolution or Noise Equivalent Temperature Difference (NETD):
The minimum temperature difference, typically specified in degrees Centigrade at
30 degrees Centigrade, an infrared imaging system is able to distinguish
between two blackbody points on a thermal image.

Thermogram: An infrared picture obtained through the use of an infrared
imaging system or other means of recording such images.

Thermography: The process of generating and interpreting thermal images.

Vapor barrier/retarder: A material used in the construction process to either
slow or stop the movement of moisture, whether in liquid or vapor form, into or
out of the building envelope or the wall structure.

Voids (insulation): Areas where no insulation has been installed.

Wind Wash(ing): Air intrusion between the insulation and the air barrier
seriously compromises the effectiveness of the insulation in framed buildings.
The long path exfiltration on the cold side of insulation allows moisture from the
air to be deposited in the building assembly.

Page 18 of 32

Appendix A (Informative)
Sample Report
(The following report can be customized to the needs of the
thermographer and the type of investigation performed.)

Date

Name
Address
Address

Re: Name
Address
Address
Insurance Company:
Policy #:
Claim #:

Infrared Inspection
Name

COMPANY A is submitting the following Thermal Imaging Inspection Report for
your approval. The report is for the above referenced facility. We hope the
information included is self-explanatory. However, should you have questions,
please do not hesitate to contact us.

Sincerely,

Thermographer/Certifications

Page 19 of 32

HISTORY
COMPANY A was authorized by NAME to conduct a limited infrared investigation
on DAY at TIME of the AREA OF THE INVESTIGATION of the HOME OR
BUSINESS at ADDRESS in CITY, STATE, ZIP. The investigation was
conducted due to concerns about MOISTURE, INSULATION, AIR LEAKAGE,
and THERMAL BYPASSES due to REASON.

The scope of work included the following components:

• A visual inspection of the damage and possible investigation of
component failures contributing to the damage
• Thermal imaging of any areas of the structure necessary to complete
the investigation.
• Moisture readings using moisture detectors, both invasive and
noninvasive, are used when possible to either confirm or deny possible
problem areas suspected through the use of the infrared camera.
• A report describing in detail the investigation, results, and conclusions.

SUMMARY OF THE INVESTIGATION
The FACILITY, HOUSE, DWELLING, ETC. was inspected with the use of an
infrared imaging device that produces thermal images as video and/or digital
pictures for documentation purposes. For this inspection, the following areas of
the building were inspected: XXXX. Any building components suspected of
being problematic are noted in this report.

Construction Design of Building
(Framing detail, wall construction detail, geographic orientation,
description of surrounding buildings, vegetation, landscape, surface
conditions, and microclimate.)

Inspection Personnel and Qualifications

The visual inspection, field notes, thermal imaging, video and/or digital
photos for documentation were completed by (NAME).

Equipment

• Infrared Camera (make, model #, serial #, calibration date)
• Blower Door (make, model #)
• Digital Manometer (make, model #, calibration date)
• Moisture Meter (make, model #, calibration date)
• Other

Page 20 of 32

Investigation Conditions

• Date and hour of test
• Ambient air temperature and relative humidity
• Conditioned space temperature and relative humidity
• Solar radiation conditions
• Precipitation
• Wind speed and direction
• Air pressure measurements and location
• Delta T
• Other relevant conditions

Standards and References

• RESNET 2006 National Mortgage Industry Home Energy Rating
Systems Accreditation Standards, Chapter 8, “RESNET Standard for
Thermographic Inspections”

INSPECTION RESULTS
The infrared camera reads radiation variations associated with surface
temperature differences of the surfaces viewed. The particular camera used by
COMPANY A has a sensitivity of X.XºC at 30ºC. In all thermal images warmer
surfaces appear lighter in color and cooler surfaces appear darker in color.

The enclosed plan of the building or area under investigation is marked for the
areas mentioned under Inspection Results. The legend is as follows:

• Blue marker: wall area
• Yellow marker: ceiling area
• Pink marker: floor area

Percentage of anomaly area for walls, ceilings, and floor sections marked on the
building plan:
1.
2.
3.

The following are a series of Thermograms and visual pictures and an
explanation of the anomaly present, why is has occurred, and necessary steps to
correct the problem.
1. Picture #1
2.
3.

Page 21 of 32

Picture #1
Company A Customer B
Just Around the Corner Address
Any Town, USA City, State Zip Code

Comments:

PROBLEM
RECOMMENDATION
INSPECTOR
ASSISTANT
CORRECTIVE ACTION TAKEN

CONCLUSIONS
The following recommended repairs are given in order from high priority to low
priority.
1.
2.
3.

Page 22 of 32

The above observations and recommendations by this inspection are based
solely on the limited data collected at the time of the inspection of the property.
The purpose of the thermal imaging for the inspection performed on your
property is to determine if problems were present concerning air infiltration,
insulation, and possibly moisture intrusion. Company A offers its opinions in
accordance with recognized building practices concerning air intrusion and
insulation anomalies. It is up to the owner or other designee to review the
enclosed data and recommendations and make prudent judgments based on
feasibility. All conclusions and recommendations are based on the data taken at
the time of the inspection and no guarantee regarding additional issues of air
infiltration or insulation anomalies found as a result of any other source present
or not present at the time of the investigation are made. Company A hereby
certifies the conclusions and recommendations expressed in this report have
been formulated by a reasonable use of building science principles and
professional certainty. The conclusions are also based on the data and
information collected at the time of the investigation along with knowledge, skill,
experience, training, and education.

Sincerely,

Thermographer
Certifications

Page 23 of 32

Appendix B (Informative)
Inspection Form for Thermal Bridging
and Thermal Bypass Investigations
Thermal Bridging (Insulation) Inspection
Time of Inspection: Delta T: Date:
Camera make and model: Square feet of anomalies:
Percent anomalies (square feet divided by surface area of insulated walls):
Comments:

Thermal Bypass (Air Leakage) Inspection
Initial IR scan performed: Yes No
Blower door used? Yes No Delta P:
Time of inspection: Delta T:
Initial blower door run time before start of inspection:
Thermal changes to building components:
1. Dropped ceilings: Yes No 2. Furrdowns: Yes No
3. Walls around showers/tubs on exterior walls: Yes No
4. Walls around fireplaces: Yes No
5. Attic knee walls: Yes No 6. Attic hot walls: Yes No
7. Skylight shafts: Yes No 8. Staircase walls: Yes No
9. Ceilings bordering rim and band joists: Yes No
10. Ceilings bordering cantilever floor areas: Yes No
11. Duct chase: Yes No 12. Flue shafts: Yes No
13. Interior walls with penetrations in top plates (attic air) or bottom plates (over
unconditioned crawl space or basement): Yes No
14. Attic access panel: Yes No 15. Recessed lighting: Yes No
16. Attic dropped-down stairs: Yes No
17. Whole house fan: Yes No
Further investigation recommended: Yes No
Comments:

Signed______________________________
Date_______________________________
RESNET Certification Number________________________

Page 24 of 32

Appendix C (Normative)
Method for Converting Anomalies to Insulation Grading
(Section 805.4, measurements converted to square feet.)

Grade II Example Wall section is 8 ft x 8 ft.
Area A Area B Area A: ½”x 96”=0.33 sqft
Area B: ½”x 80”=0.28 sqft
Area C: 1”x 12”=0.08 sqft
Area D: ½”x 12”=0.04 sqft
Area C Area E: ½”x 16”=0.06 sqft
Area F: ½”x 8”=0.03 sqft
Area G: 3”x 6”=0.13 sqft
Area D Area H: 1”x 2”=0.014 sqft

Area E
Total anomalies: 0.96 sqft
0.96 sqft / 64 = 0.015 or
1.5%

Area F Area G Area H

Grade III Example Wall section is 8 ft x 8 ft.
Areas: A B C D E Area A: 1”x96”= 0.67 sqft
Area B: 3”x16”= 0.33 sqft
Area C: 1”x16”= 0.11 sqft
Area D: 1”x16”= 0.11 sqft
Area F Area E: 1”x 8”= 0.06 sqft
Area F: 1”x 6”= 0.04 sqft
Area G Area G: 1”x14”= 0.10 sqft
Area H Area H: 1”x10”= 0.07 sqft
Area I: 2”x18” = 0.25 sqft
Area J: ½”x12”= 0.04 sqft
Area I Area K: ½”x12”= 0.04 sqft
Area L: ½”x64”= 0.22 sqft
Total: 2.04 sqft
Area L

Areas: J K Total anomalies: 2.04 sqft
2.04 sqft / 64 sqft =
0.031875 or 3.18%

Page 25 of 32

802 Appendix D (Informative)
Thermal Patterns
This section guides the thermographer in conducting thermal inspections on the
insulated wall, ceiling, and framed floor cavities in new and existing frame
construction. The emphasis will be on insulation in the building cavities that is
either malfunctioning or completely missing. The anomaly locations must be
designated on a drawing, a video, on visual and thermal images, or with a
removable marking device for ease in locating the area for correction.
1. Different thermal patterns occur as a result of differing wall conditions,
which must be identified for proper interpretation of the thermographic
images. Without knowing the exact conditions you are viewing with the
camera (summer/winter, inside/outside, transient state/steady state),
you cannot make the proper interpretation of the thermogram. The
following general descriptions of exterior walls do not take into account
any obstructions, which may be within the wall cavities.
a. The wall below with warm (lighter) wall cavity areas and cold
(darker) framing materials could be one of the following:
• Uninsulated, when viewed from outside during the heating
season.
• Insulated, when viewed from inside during the heating season.
• Insulated, when viewed from the outside during the cooling
season.
• Uninsulated, when viewed from the inside during the cooling
season.

b. The wall below with darker (cooler) wall cavity areas and warmer
(lighter) framing materials could be one of the following:
• Insulated, when viewed from the outside during the heating
season.
• Uninsulated, when viewed from the inside during the heating
season.
• Uninsulated, when viewed from the outside during the cooling
season.

Page 26 of 32

• Insulated, when viewed from the inside during the cooling
season.

c. In addition, all patterns can be reversed when solar loading has
affected the cavity.
d. Interior partition walls will normally be viewed as a consistent solid
color. The framing materials in the walls will not be distinguishable
as in the exterior walls. But anomalies may be visible when attic or
exterior air is allowed to enter the wall cavities.
2. Insulation Installed per Manufacturer’s Recommendations
b. Wall cavities will appear warmer, compared to the framing, when
viewed from the inside during the heating season and cooler,
compared to the framing, when viewed from the inside during the
cooling season.
c. Wall cavities will appear cooler, compared to the framing, when
viewed from outside during the heating season and warmer,
compared to the framing, when viewed from the outside during the
cooling season.
d. The wall cavity areas should be uniform in color throughout the
entire cavity, from top to bottom and side-to-side.
3. No Installed Insulation
a. Wall cavities will appear cooler, compared to the framing, when
viewed from the inside during the heating season and warmer,
compared to the framing, when viewed from the inside during the
cooling season.
b. Wall cavities will appear warmer, compared to the framing, when
viewed from the outside during the heating season and cooler,
compared to the framing, when viewed from the outside during the
cooling season..
c. Convection may be visible in empty wall cavities as a color variation
moving from darker at the bottom of the wall to lighter at the top of
the wall for both the cool and warm sides of the wall.
4. Missing insulation within an insulated wall will produce well-defined
shapes that will be inconsistent with the type of insulation filling the
wall cavity and the building envelope construction features and the
anomaly will have a relatively consistent temperature variation.

Page 27 of 32

5. Gaps/Misalignments are areas where insulation is partially missing or
not installed in contact with the intended interior finish.
a. These areas where insulation is missing will appear as cooler areas
on the normally warm wall cavities when viewed from the inside
during the heating season and as warmer areas on the normally
cool wall cavities when viewed from the inside during the cooling
season.
b. On the cool side of the wall inadequate insulation will appear as a
warm area when viewed from the outside during the heating
season and as a cool area on the normally warm wall cavities when
viewed from the outside during the cooling season..
6. There are several other possible causes for irregular variations of the
thermal patterns found on a wall including moisture, convection,
varying densities of installed insulation, air washing (especially with
fiberglass insulation) and thermal bridging. Note that warm or cold air
exfiltrating from the conditioned space can hide or mask insulation
defects when viewed from the interior.
7. The contrast between the stud and insulation should be consistent with
the rated R-value. Studs will show closer to the insulation shade in a
low-density application but will be consistent throughout the wall.
8. Direct sun on siding can make an interior scan of a void wall appear
the same as a properly insulated wall. Construction details and
conditions for the test must be confirmed.

Page 28 of 32

802 Appendix E (Informative)
A further visual evaluation of the following areas of the structure may be helpful
in verifying the causes and cures of problems.
1. Is the insulation installed in the building per manufacturer’s
recommendations?
2. Is there an air barrier or a moisture permeable material on the cold in
winter side of the wall and is there a possibility of subsequent
condensation and damage to wall components at this location?
3. Is the air barrier aligned with the thermal barrier throughout the
building?
4. Is there an air barrier at floor joists meeting the attic or garage or
where there are exposed insulation edges?
5. Is there slab perimeter insulation when required by code or program?
6. Are there air and thermal barriers at the rim and band joist (when
possible to determine)?
7. Is there an air barrier behind the tub/shower and fireplace?
8. Are knee walls, hot walls, and skylight shafts insulated and have
sheathing applied?
9. Is the framed floor insulation aligned properly (cantilever or over a
garage)?
10. Are plate penetrations and flue shafts sealed?
11. Are the attic access panels, drop down stairs, and doors fully insulated
and gasketed?
12. Do dropped ceilings, HVAC chases and furrdowns have air barrier
aligned with the insulation?
13. Are recessed lighting fixtures air sealed and insulated?
14. Is there an insulated and gasketed cover on any whole house fan?
15. Have the common walls between multifamily units been air sealed?

Page 29 of 32

Appendix F (Normative)

Course Content of Training and Weighting per Section
for 3-day RESNET IR certification training
Overview of Section 802 of the RESNET Standards (10% weight)
Qualities of acceptable data (6% weight)
Contents: Section 802.8
Accurate
Meaningful
Specific components
Specified conditions
Infrared camera basics (6% weight)
Basic Camera Parts
Controls
Menus
Storing Data
Range and Span
Thermal Level
Pixels
Color Palette
Hands-on practice
Heat transfer basics (8% weight)
Thermal capacitance
Conduction
Convection
Radiation
State change
Radiometric basics (6% weight)
Emissivity
Reflected background
Spatial and measurement resolution
Good measurement principles
Hands-on practice

Principles of building inspections (12% weight)
Defining the scope of service
Defining building type and components
Fundamentals (10% weight)
Conduction inspections
Seasonal differences
Interior vs. exterior
Patterns
Challenging situations
Air leakage inspections (8% weight)

Page 30 of 32

Pressure dynamics
Using blower doors
Air leakage patterns
Windows (6% weight)
Reflectivity issues
Argon depletion
Industry standards relating to IR and building inspections (8% weight)
Report and analysis software (8% weight)
Managing data
Analysis functions
Creating reports: Section 802.8, 802 Appendix A
Course test

Field Work (12% weight)
The following will guide the inspection for each building. Buildings should,
whenever possible, be representative of common building types:

Measuring and documenting conditions
Visualizing the building
Communicating with the occupants/owner
Modifying building conditions, as needed
Adjusting the imaging system for optimum results
Locating insulation
Exterior inspections
Interior inspections
Insulation types
Natural air leakage conditions
Using thermography with the blower door
Locating air leakage
Depressurization (recommended)
Pressurization (optional)
Documentation of findings
Imagery
Supplemental data
Review and discussion of work

Page 31 of 32

Appendix G (Normative)
Infrared Committee Membership and Responsibilities
The RESNET Infrared Committee with oversight by the RESNET Technical and
Training and Education Committees will have the responsibility to maintain the
process for the approval of trainers, the curriculum for the course, and the writing
of the test questions.

The Infrared Committee will be comprised of individuals who have Level II, Level
III or the equivalent experience and infrared training and will oversee the
following items:
1. The curriculum required for Method 2 of the RESNET Guidelines for
Thermographic Inspection of Buildings
2. the weighting of the categories of the questions on the test
3. the writing of the test questions
4. applications and approval of trainers
5. applications and approval of Infrared Providers
6. IR committee will make these decisions and then submit to either the
RESNET Technical Committee or the RESNET Training and Certification
Committee for approval.

Page 32 of 32

RESNET: Interim Guidelines for Thermographic Inspections of Buildings

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