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Thermal Tracking: How to Diagnose Indoor Wall or Ceiling Stains, Building Air Leaks, & Heat Loss InteriorAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• What causes those dark stains on building interior walls & ceilings? Photos & text identify thermal tracking, thermal bridging, air bypass, insulation defects and air movement in buildings
• Thermal tracking stains indoors indicate building air movement, air leaks, and points of heat loss which increase home heating or cooling cost
• How to recognize poorly insulated building walls or ceilings and how to pinpoint building air leaks
• A photo-guide to common indoor ceiling and wall stains and what they mean
• Links to more photos of indoor ceiling or wall stains that are not toxic mold

This article describes & diagnoses the cause of various interior wall and ceiling stains and explains how to recognize thermal tracking, thermal bridging stains, building air leaks, and building insulation defects. Often these stains are mistaken for toxic indoor mold. 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 but may be mistaken for more serious contamination - save your money. Because some clients have on occasion sent samples to our mold test lab that really should not have been collected, much less looked-at, we provide this library of photographs of things that are "not mold" and don't need to be tested. These are substances that you can easily learn to recognize in buildings. Save your mold test money, and increase the accuracy of your mold contamination inspection or test for toxic or allergenic mold in buildings: review these items to learn recognize non-fungal materials or even possibly harmless cosmetic "black mold" often mistaken for "toxic fungal growth." © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

A Photo-Illustrated Diagnostic Guide to Thermal Tracking & Other Wall or Ceiling Stains, & Air Movement in Buildings

What is Thermal Tracking & Why does Thermal Tracking or Thermal Staining Occur Indoors?

What is thermal tracking and what causes it? Thermal tracking or "soot tracking" such as shown in the photo at left and also in the photograph at the top of this page may be found wherever moisture condenses on cool building surfaces. Warm moisture-laden air touches the cooler surface of a building wall or ceiling, giving up some of its moisture to the surface as condensation. As air moves through the building, typically up walls and across ceilings, debris in the air, particularly soot such as that left by airborne house dust, by a heating system that needs service or by burning candles (scented candles may be more of an IAQ issue), adheres more to the damp surfaces than to others, leaving black marks or "tracks." Thermal trackng may mark the location of building framing members: In a conventionally-framed wood structure, wall and ceiling framing is typically spaced on 16" or 24" centers, and thermal tracking will tend to cause dust or soot to adhere to the interior sufaces at these locations. But thermal tracking or bridging stains may occur on different intervals depending on how the building was constructed, where air is moving, where air leaks are occurring, and whereever building surfaces are cooler or more moist. The reason thermal tracking tends to mark the location of building framing members is because the interior wall or ceiling surface will be cooler (during the heating season) where framing members (joists or studs) are located. The insulating value of wood is pretty low (about R1 per inch) compared with fiberglass insulation or other insulating materials. The sections of an interior wall or ceiling which are touching wood framing (inside the ceiling or wall cavity where a ceiling joist or wall stud was placed) will conduct heat to the outdoors faster than the "in between" sections of wall where insulation has been placed. In sum, the wall or ceiling interior surface will be cooler where the framing is located than will be the spaces which are not touched by framing and which, perhaps, are insulated. So if you see black streaks up the building wall in a regular 16" or 24" pattern, particularly on cooler exterior walls but potentially anywhere, it may be thermal tracking.

Interior stains help diagnose building conditions:: Since thermal tracking, or soot marking, or "thermal bridging" as a few folks call it usually tells us something about a lack of building insulation or about air leaks in buildings, we can use these marks or stains to learn important facts about a building:

Insulation leaks & thermal bypass defects: We use thermal tracking marks on an area where insulation is visible to identify and correct air bypass leaks, thus saving energy or reducing home heating or air conditioning costs

Insulation adequacy: Clues that suggest Insulation adequacy can be picked up easily if the observer will use thermal tracking marks on larger areas of interior walls or ceilings to tell us areas of the building that are not insulated, or are not well insulated - areas where we should consider adding or improving insulation to save energy by reducing building heating or cooling costs.

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

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - principal author/editor of the InspectAPedia ^© Website
• Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and content suggestions regarding thermal tracking.
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Building Air Leaks & Thermal Tracking Marks at Interior Ceilings

Sooty or dark smudges or stains appearing near the ceiling on the inside of building exterior walls, especially in older homes whose interiors have not been re-painted or cleaned in some time. Thermal tracking stains may appear at the top of the wall and extend onto the ceiling surface such as shown in this photograph. Note those dark "stripes" extending along the ceiling and into the room? These ceiling stains probably mark the location of ceiling joists (where the in-room ceiling surface temperature was kept a bit cooler since these locations in the ceiling cavity are occupied by a wood joist rather than by insulation).

Air Leaks Causing Thermal Tracking Stains on Building Walls

Thermal tracking stains may appear on the building walls themselves, in a pattern of vertical "stripes" which may be roughly 16" or 24" on center, marking the (cooler) location of wall studs or ceiling joists. Thermal tracking stains may appear as dark black/brown wall stains appearing close to floor level, above heating baseboards mounted on exterior walls are probably due to thermal tracking.

Heaters can cause other dirt or soot stains on walls: But beware, a baseboard heater itself causes an air convection current up through the heating baseboards and in a dirty home or in a home occupied by pets or smokers similar stains may appear on other building interior walls (such as in this photograph) even if the wall is well insulated. If staining appears vertical and at intervals thermal tracking is probably occurring.

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

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

How to Use Indoor Stains Like Thermal Tracking to Diagnose Building Air Leaks, Insulation Defects, and Indoor Air Quality Problems

Significance of Other Indoor Stains and Marks for Building Framing Location or Defects in Heating & Cooling System Operation

Since thermal tracking, or soot marking, or "thermal bridging" always tell us about missing or openings in building insulation or about air leaks, we can learn other facts about a building such as those listed here:

• Location & spacing of building framing members. Indoor stains can help find the location and spacing of wall studs or ceiling joists: use thermal tracking marks on building interior surfaces to spot the location of wall studs or ceiling joists when we need to find those members (for placing a picture nail, for example). Observing the spacing between these stains can tell us how a building has been framed.
• Identify unsafe heating equipment or poorly-functioning fireplaces: use thermal tracking marks on interior building walls and ceilings, particularly where they vary from room to room, to diagnose poorly-vented chimneys such as fireplaces that do not work well (also look for soot stains at the hearth face). Such marks may also indicate poor and even unsafe operation of central heating systems since a poorly maintained oil burner will often leak soot into a building interior, and a dangerously un-vented gas appliance may also produce both soot and potentially fatal carbon monoxide gas.

How "Read" Indoor Stains to Identify Indoor Air Quality Concerns

A careful examination of the location of indoor stains permits the observer to use thermal tracking or soot marks on building walls or ceilings as an indicator of possible excessive (seasonal) interior moisture or other potential indoor air quality concerns.

Dark stains on building interior walls may appear in other patterns and could be from other causes - we provide photographs, description, diagnosis, and advice for many of these indoor stains in this article.

How to Diagnose Stains and Debris at Ceiling and Wall Heating or Cooling Air Supply Registers

Dirty HVAC duct work, lack of air filter maintenance, or furnace malfunctions can all be indicated by black stains that appear around warm or cool air delivery registers in building ceilings or walls. (This is usually a deposition of house dust, rarely is it mold, and rarely is it related to thermal tracking. An investigation of what was at first called Killer House Dust from an HVAC system showed that the dust of concern turned out to be cotton and other carpet fibers having nothing to do with the Heating or Cooling equipment was discussed at our Fear of Mold WebLog or "Blog" where we periodically post results of interesting forensic investigations.

How to Recognize Pet Stains on Building Walls

Evidence of pets in buildings: In buildings where pets are or have been housed, smudge marks on walls and at doors and door trim are sometimes mistaken for thermal tracking - they are not, but these marks, along with others (scratches, urine stains) can tell us the history of pet occupancy in a building, information of use when investigating indoor air quality concerns, especially in spaces occupied by asthmatics or people with pet allergies. Black marks on interior walls such as painted drywall might be just be where the dog lay on the floor against the wall (as shown in this photograph).

How to Recognize Wall Stains from Human Occupants

Black marks on interior walls such as painted drywall might be also be dark wall stains where people rested their heads in bed (as shown in this photo). Look at the location of these stains and imagine a bed having been placed with its head against the wall shown in the photograph. Notice the two wall lights. This is where a bed was almost certainly placed, and we can easily explain these black stains on the drywall. No further testing would be appropriate in normal circumstances.

How to Recognize Wall or Ceiling Stains due to use of Candles, Woodstoves, or Fireplaces

• Excessive indoor humidity: If indoor humidity is too high we may be encouraging mold growth in a building or we may be inviting excessive levels of dust mite activity which in turn increases the level of allergens in the building.

Other Sources of Dark Stains on Indoor Walls & Ceilings

If you have frequent fireplace fires, cooking, or if you burn scented candles, if people smoke in your home, or if your oil-fired or gas-fired heating system is not working properly, the added soot particle load in the building air is not only a health concern (soot and potentially lead), it also will mark the building surfaces in this characteristic pattern.

More Information on Finding and Identifying Mold in Buildings and Building Diagnostic Inspections and Repairs

• Attic Condensation and Ice Dam Leaks - Detection and Correcting Venting and Condensation Problems in Buildings
• Insulation Inspections: Insulation in Buildings: Identification, R-values, Heat loss, Insulation Types, Insulation Characteristics
• Asbestos pipe insulation in buildings
• Brick "Insulation" in Building Walls
• Heat Loss Calculations, Insulation Properties, Definitions of R, K, U values, Insulation Design
• How to Detect and Correct Attic Condensation & Prevent Ice Dam Leaks in Buildings
• Insulation Materials as Indicators of Building Age
• Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
• Insulation Identification Photographs - Fiberglass insulation photos, yellow, pink, green, white fiberglass identification in building attics, walls, ducts, other locations
• Insulation Identification Photographs - Cellulose insulation photos, Mineral wool insulation photos, rock wool insulation photos, cotton insulation photos, balsam wool insulation photos
• Insulation Identification Photographs - Vermiculite insulation photos
• Insulation Properties, Table of R-Values, density, moisture permeability, fire safety, aging effects on various insulation materials
• Mold in Fiberglass in Insulation
• Radiant Heat Floor Mistakes to Avoid case history of improper placement of slab insulation and radiant heat tubing
• Thermal Trackingthermal bridging & air leak stains in buildings or on building insulation
• Un-Vented Roof Solutions - How to Prevent Attic Condensation, Ice Dam Leaks, Roof Mold, & Roof Structural Damage in Buildings with Un-vented Roof Cavities
• Vermiculite Building Insulation & Asbestos
• Ice Dam Leaks in building attics and roof cavities, how to inspect for evidence of leaks, identify causes, and correct bad attic ventilation, improper roof venting, and these causes of attic mold or roof structure damage
• Looking for Mold what mold is often found where in buildings - simple technical presentation
• Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
• Recognizing Allergens: What various indoor allergens look like - identification photos to help identify pollen, dust mites, animal dander, toxic or allergenic mold - Common Mold and other Allergens, Irritants, Remedies & Advice
• Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
• Animal Allergens: Dog, Cat, and Other Animal Dander - Cleanup & Prevention Information for Asthmatics and regarding Indoor Air Quality.

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

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