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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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.
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.
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.
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 BRIDGING GHOSTING - home
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.
GHOSTING DARK STAINS on INSULATION, AIR BYPASS LEAKS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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(Oct 2, 2014) Sam said:
Wow, what a great resource, thank you so much for all the info! Question: Garage ceiling has this tracking at all the drywall seams. I can see that the ceiling was insulated. Dark spots exactly correspond with the 12" joint compound finishing knife. Could it be that the compound was simply not sealed properly when it was painted? Also, could exhaust from cars cause this-it's nowhere else in the house.
Thanks, I love this site!
I don't think so. More likely the joints are over studs, pipes, or cooler surfaces that pick up a bit more moisture and thus particle deposits thus stains.
Yes car exhaust could be a particle source, also a moisture source. And if the car is burning oil and is left running for some time in the garage these effects would be increased.
Watch out: for potentially fatal carbon monoxide hazards if car exhaust can enter the home or accumulate in the garage.
(Jan 17, 2012) John Dabbs said:
A friend has black deposits appearing evenly on vertical surfaces at the top of an internal lounge wall, just under the coving. The wall-hung pictures also have severe dirt 'shadows'. The appearance is similar to that I experienced when I had a de-ioniser in use in my bedroom, but there is none in the friend's lounge but there is a tv and modern wall-hung logfire-effect unit. Heating is by conventional hotwater radiators. The house is right on the sea front (at Bude) and fully exposed to off-sea winds. Could the cause be thermopherosis? Caused by deionisation from sea spray? Or what? And what might the solution be? No nearby pollution source that I can identify.
John, if by "appearing evenly" you mean at even spaces or intervals such as marking the intervals of building framing members, that would be a classic diagnostic clue indicating thermal tracking.
And yes, using a "de-ioniser" (more likely it was an ionizer - a device that puts an electrical charge on dust particles, causing them to plate out on wall and other building surfaces) can contribute to soot and thermal dust tracking stains on building walls and ceilings.
I'm not sure of the role that off-sea winds would play in thermal tracking - it depends ... for example on the effect of winds on building heat loss. Sea spray itself sounds an unlikely cause to me as I don't imagine much sea spray enters the building interior.
Even common house dust will be enough of a particle source to explain thermal tracking in buildings, but where there are additional dust or particle sources the effects will appear more rapidly and at more extreme levels. Examples include an oil burner that is not working properly, producing soot; use of candles, scented candles, woodstoves, fireplaces, or even burning cooking materials. Pets can also be contributors.
The solution to thermal tracking includes:
- identify and remove sources of high levels interior dust or particulate debris as much as possible
- identify locations of building air leaks and heat losses and correct them
- add insulation, particularly where there are voids
- monitor and correct high levels of interior moisture
Many thanks indeed, Dan, for your comments. Perhaps I should have said that the staining is "uniformly" spread ie a consistent level along the upper perimeter of the room, graduating in intensity as the ceiling is approached. The wall construction is, I believe, solid masonry (I'll check that), and the effect is apparent on all walls whether internal or not. One wall - facing the sea - has a large double-glazed sliding patio door and a "soot" film appears on this after only a few days after cleaning.
Yes, I should have referred to an ioniser - I apologise! It was because of the similarity of this problem to my previous experience with one of these that I was wondering if this was due to an ionising effect somehow. Hence I was wondering if excessive sea spray could cause ionisation? Clutching at straws? The household has a cat, but it's a large, open house. The room is clean with few furniture pieces, all modern, with a fitted carpet. There are a few nearby properties, all as far as I know with natural gas heating. Completely residential area, and I can't identify an probable sources of dirt/soot particles, but I'll have another look around. No woodfires, candles or oil burners. Two of the walls have hot water radiators fixed to them, but the staining is at the same level on a third wall with no heating fixed to it.
Any further thoughts?
(Feb 26, 2012) Jerry said:
How do I clean painted wall from streaking
Jerry, identify the cause, fix that source first; then wash and seal and paint the walls. You might want to use a lacquer primer sealer for best results.
Apr 7, 2012) sue white said:
we have a friend with a house that has ghosting at the 2nd floor ceiling and top 1-2' of wall where it meets the ceiling; the nails are also popping at this ceiling/wall juncture. the house is entirely electric with exception of a gas fired stove in the lower level of the split level home.
do you think the ghosting is due to a malfunction with the stove or some other issue? thank you
Not likely - but
Watch out: a gas cook stove that is making visible soot is not working properly and is unsafe, risking fatal carbon monoxide poisoning.
(Feb 20, 2014) Anonymous said:
how does one get ride of thermal tracking.
Good question, Anon.
First, the actual black sooty marks can be removed by cleaning washable surfaces; typically we use a non-sudsing detergent. On carpets the carpet would have to be shampooed.
But to complete the "get rid of thermal tracking" process we need to look at what is causing the soot or dust marking and address the underlying causes (which are discussed in this article series).
As some examples:
- look for and fix any extra sources of dust or soot like a poorly-tuned oil burner, use of a fireplace, scented candles, smoking
- check the indoor humidity level and if it's too high we need to fix moisture sources or dehumidify the building - see HUMIDITY LEVEL TARGETS
- See THERMAL TRACKING REMEDIES for complete details
(Feb 24, 2014) Sarah said:
My husband and I just notified a stain on the ceiling that wasn't there 7 months ago when we moved in. It's a light pinkish tan stain on a textured ceiling. It is about 3 ft shy of an air vent in our breakfast nook. It does look like a type of moisture stain but nothing similar to your mold patterns you've posted pictures of on the website. This is a ceiling below our guest bath. Any ideas?
Sarah, I'd have to see some sharp photos (you can use our CONTACT link if you like);
Generally the location and size of a ceiling stain will suggest something about possible sources, e.g. a possible leak from above.
4/2/14 Kathy said:
we have been experiencing the same we moved to a house 2 yrs ago and especially during the winter it seems to get darker marks. this winter we noticed it a lot more. I have pictures but unsure how to load them here. we see the ceiling marks by the beams as well as the corner marks or above the heat. should we be concerned?
You can use the CONTACT link at page bottom to send us photos. I'll take a look.
(Oct 7, 2014) Brennan said:
Have you ever seen this in carpet in the middle of a room (not near the baseboards). I received a moisture meter to check some ceiling stains to see if they were active or inactive after the former owner replaced the roof. I was using the moisture meter to check the basement- all surfaces. I found some areas in the basement carpet where the moisture meter was high but dry to the touch. I run a humidifier in that room and it doesn't work very hard to maintain 45-50 rh%
It has a 'line' type stain. A bit darkened (carpet is grey, so this is darkish grey), but not like the other areas where there is actual infiltration soiling (I have seen it is one room near the baseboards but is completely dry). My home is old, so of course it has air leaks.
The former owners had a couch over this area, so I thought it was due to that. Adjacent staining is yellow coloring and also shows moisture in the meter. So moisture and a line/ghosting in carpet. The carpet is gross anyway, so I thought about peeling it back to see if there is a crack in the slab (60+ yr old house). A contractor friend, without seeing it, said it was radon gas escaping. That seemed like a stretch, since Radon is colorless. I think though, perhaps he meant, air is feeding through the crack and depositing soil on the carpet.
If I do find a crack- should is seal it with concrete/caulk and re-carpet and be vigilant about dehumidification?
A couple of points to consider:
Most moisture meters, if we exclude thermal imaging, rely on measuring differences in electrical resistance to detect moisture. But other contaminants or materials can also decrease resistance in an area of building material. So not every reading variation is necessarily truly detecting moisture. Some attention, particularly looking for possible moisture sources, are key.
Both pin type moisture meters (Delmhorst for example) and electronic moisture meters (such as some Tramex meters) can be fooled by metal nearby: pipes, foil faced insulation, wiring.
Second: no moisture meter, nor thermal imaging device, can detect old leaks that have since dried, even though the leak might have initiated a building problem with rot, insect damage, or mold contamination. This is why we argue that reliance on meters and imaging alone for water or mold detection are unreliable. But the instruments are indeed useful, in thoghtful hands. And neat too.
(Oct 9, 2014) Brennan said:
Thanks for your comment. One thought (using my science background) was that the moisture meter gives a high reading on what looks like an old dog urine stain (former owner had dog). I had the thought that these left over salts and ions from the urine might act as a weak conductor and activate the moisture meter. On the internet, it seems that carpet companies use moisture meters to find hidden pet stains, because the salt from the urine can draw moisture from the air (or even just the natural evaporation of the concrete slab). So, thanks for your help. I tend to over-think things. I agree, it is a neat tool.
(Oct 9, 2014) (mod) said:
Interesting Brennan, and thoughtful. I agree with the salts / ions theory for both of the reasons you offer.
It's not over-thinking. The more we understand the better we can find and fix or prevent aggravations. Thanks.
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