Ghosting or Mold Growth?
While interior mold growth on the ceiling is often obvious, there is another building defect that can look eerily similar. It’s called ghosting. It occurs when soot and dust particles stick to the ceiling. Over time, these particles cause a permanent stain. The clue is in the pattern – ghosting often appears in perfectly straight lines.
Why? The lines correspond to the framing in the attic above. Because the framing is a worse insulator than the surrounding fiberglass, a cold spot forms wherever the framing touches the ceiling. The colder temperature leads to condensation, which causes the soot and dust particles to stick.
Ghosting from lack of ceiling insulation
While ghosting often mirrors the attic framing/rafters, it can also occur due to missing insulation. The photo below is an example of this scenario. Notice how the grey, discolored area matches the exact width of the attic rafters. Insulation is missing in this section, leading to a decrease in temperatures and condensation.
Thermal imaging cameras are excellent at detecting the missing insulation that leads to ghosting. Notice how the colored spots in the thermal imaging on the left match the discolored ceiling on the right. The temperature differences are due to missing insulation (warmer in this case because the inspection was performed in the summer).
Ghosting can produce other unusual results. Often homeowners will report dark circular spots above vanity lights. This is due to the updraft of air currents created by the heat of the light bulb. As the air moves upward, it carries dust and soot particulates. As the air impacts the ceiling it quickly cools, leaving the dust particulates (and staining) behind.
How do you stop ghosting?
- Stop using candles or combustible oils. In most cases, these are the two culprits.
- Improve your attic insulation. Ensure the insulation covers the ceiling joists/rafter ties. In many older homes with batt style insulation, the tops of the joists are exposed.
- Lower your interior RH. The issue is exacerbated by the excess humidity in the air. If you live in a climate with cool winters, ensure you are properly ventilating your home. Often this can be achieved by simply running a bathroom exhaust fan.
- Excellent explanation on Building Science’s website
Project Report > Inspection for Ghosting Issues
Work #: 202008
- Staining noted on carpeting immediately adjacent to master tub, this may be secondary to leakage from the poorly caulked areas.
- Damaged paint and sheetrock around window is evidence of previous water intrusion.
- Exhaust fan located near shower.
- Assess window for potential of future leakage.
- Replace exhaust fan.
- Moderate surface growth noted on exterior wall in closet.
- 2 exhaust fans located in this area.
- Vinyl flooring near tub heavily stained.
- Caulking around tub shroud in poor condition.
- Heavy surface mold growth noted on exterior wall, furniture had likely been placed against the wall in this area.
- Major ghosting noted on walls and ceiling, this is symptomatic of a poorly insulated and humid home.
- Fireplace located in this area.
- Large crack in ceiling sheetrock near entrance to hallway, likely secondary to normal building settling.
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My walls have green lines on them.
Ghosting typically causes black, not great lines. If you’re observing green growth, this is likely due to mold growth. The same conditions that cause ghosting (condensation, high humidity, etc.) can also lead to mold growth. Purchase a relative humidity gauge and try to keep the RH below 55%. In most climates this can be achieved by simply increasing the ventilation in the home. Running your bathroom 12 hours per day will often do the trick.
Is this ghosting or mold on my cathedral ceiling?
This looks like ghosting. Mold growth typically has a spotting pattern, whereas ghosting has a grey, diffuse appearance. If accessible, check the ceiling from the attic. I’m guessing you’ll find these spots correspond with areas of missing insulation. Lowering the indoor humidity will also help reduce ghosting.
Is this ghosting?
The angular pattern and color are both indicative of ghosting, not mold growth. The ceiling cavity is likely missing insulation, which is causing condensation and ghosting. If accessible, add insulation in the area above the ghosting. If not, focus on lowering the indoor humidity.
Do I need to treat outside before I treat inside ghosting? Also, do the air heaters make it worse?
There is no need to treat the outside first. Ghosting often occurs above radiant or baseboard heaters. As the air is heated, it absorbs moisture from the adjacent areas. The problem occurs when the air cools as it travels upward. At some point it reaches the dewpoint and can no longer hold the water in vapor form. The water is released from the air as condensation. This condensation attracts dust, soot, etc. and causes the visible ghosting. Instead of lowering your heat, focus on lowering the humidity in the home. In most cases this will eliminate the ghosting.