Air bypass leak stains on building insulation © Daniel Friedman Building Air Leaks Cause Indoor Wall or Ceiling Ghosting Stains
Building Air Leaks & Heat Loss Points show up as lines, spots, dark areas, stains

  • GHOSTING DARK STAINS on INSULATION, AIR BYPASS LEAKS - CONTENTS: Ghosting Marks: (also called thermal telegraphing 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.
  • POST a QUESTION or READ FAQs about indoor stains and thermal tracking or ghosting on walls and ceilings

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Air leaks into walls, ceilings, or bypassing insulation can cause Indoor stains or dark areas on building insulation:

Because building air contains normal house dust and often other particles such as soot or animal dander, the location of stains caused by ghosting or thermal tracking or air bypass leaks can help locate air leaks, insulation air bypass leaks, and similar air unwanted air movement. Correcting these air bypass leaks saves building energy cost and stops the staining.

This article series describes & diagnoses the cause of various interior wall and ceiling stains and explains how to recognize thermal tracking, (also called ghosting or ghosting stains or thermal bridging stains), building air leaks, and building insulation defects.

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Role of Building Air Leaks in Thermal Tracking Marks at Interior Ceilings or Walls

Air Leaks Causing Thermal Tracking Stains on Building Walls

Photograph of thermal tracking on an indoor wall

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.

See WALL THERMAL TRACKING STAINS for details of diagnosing stain patterns on building walls and above heat sources.

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.

Black Stains on Insulation: Air Bypass Leaks

Air bypass leak stains on building insulation © Daniel Friedman

Air bypass leak identification: Thermal tracking may also mark the location of air bypass leaks - often a more significant source of building heat loss than thermal bridging at solid joists or studs.

If a building top floor ceiling or exterior wall has many air leaks, even though the building is supposed to be well-insulated, the total of all of these air leaks may in fact add up to the same heat loss as leaving one or more windows or doors open in freezing weather.

Air Bypass Leaks Marks on Insulation (such as our photograph) shows how to identify air bypass leaks by the dust marks left on building insulation. These black stains are from building dust deposition; in this case they are not mold.

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

Photograph of thermal tracking on an indoor wall

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.

See INSULATION STAINS - AIR BYPASS LEAKS for details of diagnosing stain patterns on building or on building surfaces where insulation is missing or poorly installed.

See MOISTURE PROBLEMS: CAUSE & CURE for an explanation of moisture sources and movement in buildings.

Article Series Contents


Continue reading at HUMIDITY ROLE in GHOSTING STAINS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see WALL THERMAL TRACKING STAINS - diagnosing ghosting stains on walls


Or see THERMAL TRACKING REMEDIES - curing ghosting stain problems in buildings

Or see AIR MOVEMENT in BUILDINGS - When, where, how & why air moves in buildings.

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