How to Diagnose Building Air Bypass Leaks in Insulation - Building Energy Cost Impact

How to Recognize & Diagnose Air Bypass Leaks Marks on Insulation - stains can indicate un-wanted heat loss (or heat gain) due to air leaks
- How to recognize poorly insulated building walls or ceilings and how to pinpoint building air leaks
- Black "mold" stains on building insulation may be house dust deposited by air bypass leaks
- Black or gray stains on building insulation in attics, walls, or other areas often indicate points of building heat loss due to air bypass leakage
AIR LEAK DETECTION TOOLS - separate article
AIR LEAK MINIMIZATION - separate article
AIR LEAK SEALING PROCEDURE - separate article
ENERGY SAVINGS in buildings - separate article
HEAT LOSS DETECTION TOOLS - separate article
HOUSE DOCTOR, how-to be - separate article
THERMOGRAPHY IR Infra Red & Thermal Scanners - separate article
THERMAL IMAGING, THERMOGRAPHY - separate article
WINDOW / DOOR AIR LEAK SEALING HOW TO - separate article
Questions & Answers about air bypass leak stains found on building insulation and in other locations.
References

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Thermal tracking stains indicate air leaks or heat loss: this article describes How to Recognize & Diagnose Air Bypass Leaks Marks on Insulation and discusses other interior wall and ceiling stains and explains how to recognize thermal tracking, thermal bridging stains, building air leaks, and building insulation defects. Our page top photograph shows black air-bypass leaks on building insulation in a wall. Often thermal tracking stains are mistaken for toxic indoor mold, especially when they are even more "black" than in our page top photo.

How to Recognize Air Bypass Leaks and Thermal Bridging Marks on Fiberglass Insulation

Photograph of thermal tracking on an indoor wall

Black, brown or gray stains on building insulation

We have frequently observed evidence of air bypass leaks and thermal tracking as black or gray dust deposition on attic insulation, a condition some owners have mistaken for mold (and wasted money on mold testing and remediation).

In this photo (left) we've removed a "nearly new" insulation batt that was installed in a cantilevered floor which was leaking air up through the overhanging floor and into the building wall cavity. In just a month of exposure the insulation is already showing dust tracking at its lower right corner, marking the air leak path in this building.

Gray or black marks on or in building insulation, particularly fiberglass insulation, we see thermal tracking as grayish deposits (actually house dust) left where air is leaking from the conditioned space into the unconditioned space (say from a top floor bedroom into an attic floor and attic above).

The warm air passing by the insulation leaves house dust which sticks by moisture condensing out of the warm air and onto the fibers, or the debris may adhere simply by static to the insulation fibers.

On building insulation, debris stains left behind by thermal tracking will show us where we have air bypass leaks in a building, such as around ceiling light fixtures, electrical box openings, or where the insulation blanket was not uniformly and thoroughly installed.

When investigating a building for a mold problem, you can save mold test costs by learning how to recognize Stuff that is Not Mold or is only Harmless Mold (MOLD APPEARANCE - STUFF THAT IS NOT MOLD) but may be mistaken for more serious contamination - save your money. Moldy building insulation is discussed in detail beginning at INSULATION MOLD

Readers should see HEAT LOSS in BUILDINGS. Also see AIR SEALING STRATEGIES and AIR LEAK DETECTION TOOLS as well as AIR LEAK MINIMIZATION. For photos of snow melt on rooftops that also show points of building heat transfer and loss, see STAIN DIAGNOSIS on BUILDING EXTERIORS.

Look at the Insulation Stain Location and Patterns to Diagnose Insulation Marks or Stains

If the stains are usually around the edges of insulation batts in a wall or attic floor, they may be due to air bypass leaks around or close to building framing.

The insulation stain photograph at left was contributed by reader M.B. Notice that the black marks are only on the edges of the fiberglass batts. We suspect these marks are due to a combination of

Air and heat bypass leaks where the insulation batts abutted attic or wall framing
Perhaps in an older home or
Perhaps in a home subject to high levels of dust or even soot from a heating system malfunction
Perhaps in a home where other conditions (improper attic ventilation) caused abnormally high levels of warm air movement and heat loss upwards through the building

Look for Obvious or Subtle Insulation Voids - Even Small Ones

Small openings along building framing where insulation has not been uniformly installed often form thermal bypass points or leak points that move warm building air into the cooler space, depositing airborne housedust in the insulation as it passes by.

Look for water or leaks that may have wet building insulation to Diagnose Insulation Stains

If insulation has been wet it may indeed be moldy. But if the stain pattern on attic or wall fiberglass insulation does not track to building leaks, be sure to consider air bypass leakage instead.

On the other hand, if insulation is visibly water or leak stained, or is below or adjacent to an area that has been wet from roof leaks, plumbing leaks, or wall leaks, then it may indeed be moldy. The first place that we see mold on building insulation is often on its kraft facing, particularly if the facing is the non-foil type facing paper.

Insulation that is stained and perhaps moldy due to building leaks may show water marks, debris, even rot or insect debris from adjacent wet or damaged surfaces right in the area that has been wet, and not elsewhere. But mold contamination may be more extensive (if not visible) in previously wet insulation. See INSULATION MOLD.

Our photo at left shows modest staining at a building eaves where insulation was pulled back; these stains may be due to ice dam leaks and may have wet wall cavities.

Certainly if the insulation is left in this position we can expect to see (in the finished space below this spot ) thermal tracking or ghosting stains on the building ceilings where insulation is missing.

Testing stained building insulation insulation to identify whether or not the "stain" is mold, dirt, insect debris, animal urine, or something else, is certainly possible, but it should not be necessary in most cases and may not be cost justified.

We welcome more thermal tracking, soot tracking, air bypass leaks, and similar photos of indoor stains as well as text suggestions to expand this detail and would be glad to credit contributors. CONTACT us to contribute or ask about air bypass leaks and insulation stains.

Usually soot marks, thermal bridging, or thermal tracking stains appear, if at all, in the building interior locations discussed in the remaining sections of this article.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and content suggestions regarding thermal tracking.

Thanks to reader Mark Bowlby for discussing insulation stains, insulation mold and mold testing procedures - July 2010

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
- 2005 ASHRAE Handbook : Fundamentals : Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
- 2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
  by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
  "2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
- 1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
  "The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
- Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 AShrae Handbook - Fundamentals (Hardcover), Harry J., Jr. Sauer (Author), Ronald H. Howell, ISBN-10: 1931862923 or ISBN-13: 978-1931862929
- 1993 ASHRAE Handbook Fundamentals (Hardcover), ISBN-10: 0910110964 or ISBN-13: 978-091011096
Dust from the World Trade Center collapse following the 9/11/01 attack: the lower floors of this building contained spray-on fire-proofing asbestos materials.
Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
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