Mold Growth on the Ceiling
Moisture and mold problems can occur on the ceiling for a variety of reasons. For the sake of clarity, let’s look at the most common ceiling problems in two broad categories: 1.) Humidity. 2.) Liquid moisture.
Humidity problems occur when warm, moisture laden air interacts with a cool ceiling, causing condensation and subsequent mold growth. Liquid moisture problems are due to direct liquid water exposure, i.e. plumbing failures, roof leaks, etc.
Occasionally the mold growth is due to a combination of both factors. In the photo above, ceiling mold was due to an extensive flooding event while the home was unoccupied. Although the water never touched the ceiling, the flooded flooring created extremely high humidity throughout the entire home. Over time, mold growth occurred on the ceiling.
First, is it really mold growth?
While 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 joists in the attic above. The framing is a worse insulator than the surrounding fiberglass, which passes through to the ceiling below. The colder temperature leads to condensation, which causes the soot and dust particles to stick. Still unsure whether or not you’ve got mold? Read our guidance on mold testing.
Ghosting from cigarette smoke:
Cigarette smoke can cause staining via the same principle as ghosting. The soot attaches to cold spots on the ceiling. In this case, it was due to areas of missing insulation in the attic. Cleaning soot from ghosting is extremely hard. Typically your only recourse is to repaint.
Ceiling mold growth is typically black. If you look closely, you can often see the filaments from the fungal structure. Mold growth also requires higher humidity/moisture than ghosting.
Identify the cause of ceiling mold growth
Common in older homes, excessive humidity and poorly insulated ceilings can lead to mold growth on ceilings. Mold growth due to humidity (as opposed to liquid moisture) is often identifiable by the growth pattern. A trained professional can usually diagnose the cause of ceiling mold with just a quick glance. The following are clues for each of the moisture source.
Symptoms of humidity based mold growth:
- Mold growth is worse at the perimeter of the room
- The room is on the top floor
- The attic is poorly insulated
Symptoms of mold due to roof leaks:
- Discoloration is brown/yellow
- Mold/staining follows as circular pattern
- Mold growth is confined to a single region
- Discoloration is brown/yellow
- Mold/staining follows as circular pattern
- Mold growth is confined to a single region
Identify the extent
Condensation based ceiling mold:
If the mold growth is due to elevated airborne moisture, the extent of the mold growth will be readily discernible from the interior of the home. Just stand in the middle of the room and look up. If you don’t see mold, there won’t be mold on the other side of the ceiling. Mold testing is often recommended in these situations.
Liquid based ceiling mold:
The opposite is true for roof leaks, pipe leaks, etc. Far more mold growth may be present on the backside of the sheet rock than the side facing the room. A visual inspection of the backside of the ceiling is the only way to properly identify the extent of the mold growth.
Occasionally we encounter a noteworthy project that creates unique challenges. Often these are due to mold problems in specialized buildings. In this case, the water loss and mold damage occurred in a dedicated media room. While entertaining for the home owner, home theater rooms always present difficulties due to the sound deadening materials used in the ceiling and wall cavities. In the diagram below you’ll notice several unusual items. 1.) Inner floor insulation. 2.) Additional layer of particle board. 3.) Upholstered fabric
Dryout of this ceiling/floor system required far more work than typically called for in a water intrusion. As you can imagine, once moisture enters the interior of the ceiling cavity, it won’t readily leave.
Remediating mold growth in ceilings.
First, identify whether or not the ceiling in question contains insulation. If the ceiling is on the top floor of the home, it is likely insulated. One caveat: top floor ceilings may lack insulation if the attic insulation is located on the roof sheathing. However, this is an unusual arrangement. Inner ceilings are typically uninsulated. Exceptions to this are occasionally found when a second floor was installed at a later date. Also, some homes have insulation on interior ceilings for sound reduction purposes.
Uninsulated, inner-building ceilings are both less likely to support mold growth and easier to remediate if mold growth does occur. If you’ve spent any time on this site you know that mold growth requires both a food source and available moisture. Sheetrock, especially the paper on the backside is an especially welcome food source for mold. Thus, we’re left with moisture as the controllable factor. This is where uninsulated ceilings show their advantage. Because they lack insulation, air is free to move on both sides of the sheetrock, allowing dryout to occur much more rapidly. Additionally, if mechanical dry out techniques are necessary, such as dehumidifiers and air movers, the free air allows for exponentially faster moisture removal. Remember though, we’re not talking about uninsulated top floor ceilings.
Replace or repair?
The first choice encountered in a ceiling remediation project is simple. Is the ceiling material salvageable or does it require replacement? In general, if the mold growth is due to liquid water intrusion (i.e. roof leak), replacement is recommended. If the mold damage is due to condensation, the ceiling can often be repaired without replacement.
If replacement is warranted, contact a professional mold remediation company. Removing a ceiling can introduce a tremendous quantity of mold spores into the indoor air, and thus, containment is necessary. If cleanup is appropriate, small jobs under a couple square feet may be undertaken by a homeowner.
"Hello...we had insulation blown into our attic. We are concerned if there was mold before the insulation was installed. How do we check that. "
It’s very unlikely mold would grow beneath the insulation. Condensation is the most common cause of mold growth in an attic. Condensation occurs on the underside of the roof sheathing, not beneath the insulation. Mold growth beneath the insulation would require a roof leak, which you’d typically notice on the ceiling inside the home before any real mold growth occurred.
During Hurricane Harvey the paint and sheet rock on the ceiling in our guest bathroom began to peel and crack. We looked in the attic and discovered the roof was leaking through the nails holding our shingles in place. Now we have spotted what appears to be mold spots adjacent to the cracks in the ceiling. Any suggestions???
I would first verify you actually have a leaky roof. Drips from the nails are often due to condensation. Because the metal nail is the coldest part of the roof, the water will condense on the nail first. Check to see if the water on the roof sheathing is uniform throughout the attic. If so, it’s likely condensation. If it’s limited to specific areas of the roof, it’s likely a failure of the roof shingles.
You mention mold spots adjacent to the cracks in the ceiling. Are these spots in the attic or in the ceiling itself?
I have a 3 story home with an attached garage off to the side which has it's own roof above and inside my garage I'm seeing mold in two different areas but no water stains at all. Any clue why?
Mold in a garage is fairly unusual. Are you seeing mold on the ceiling or somewhere else? What region of the country are you located in?
If the mold is on the garage door, it’s due to condensation from excess humidity in the winter. Installing a low-CFM constant flow bath fan in the exterior wall will solve the problem.
If the mold is on the ceiling, I recommend investigating it as a roof leak. Mold due to condensation is very unusual in the garage because there is typically no moisture source (as opposed to the occupied portion of the home).
Hi, There are small black mould spots stains not too far away from the centre of our bedroom ceiling. Are these as a result of issues with attic above or condensation, many thanks.
There are 3 potential options: roof leak, condensation, or ghosting. Roof leaks are usually obvious because eventually you’ll see an actual drip. However, a very slight leak can cause mold growth without leading to actual dripping. Does the ceiling feel wet to the touch? If you have access to a moisture meter, scan the suspected area. The more likely cause is condensation. This can be due to inadequate insulation in the attic (which can be verified by the unpleasant task of crawling to the area above your room). If you see missing or insufficient insulation, simply add a fiberglass batt.
Excess humidity can also cause mold growth on the ceiling, even in a well insulated attic space. Purchase an inexpensive RH meter and monitor the humidity levels in the room. The 3rd potential cause is ghosting, which is not actually mold (though it can look very similar). Ghosting occurs when small soot particulates from candles, fireplaces, etc. collect on damp areas of the ceiling. This occurs on cold spots, such as areas with missing insulation. It is not a health issue and can be corrected by lowering the humidity inside the home and/or adding insulation to the attic.
Can I spray bleach and wipe off little green mold spots that appear in my living room ceiling?
Yes, but it’s critical you determine the cause of the mold growth. See the answer above for the 3 potential causes of mold growth on the ceiling.
Hello, we have black mould on the wooden framework of the bedroom window which has been there for over a year. I have used Ronseal mould killer on it but the mould path is still there. Are these harmful in terms of emitting mould spores or are they just stains/patches?
Mold growth often leaves behind stains in the underlying material. This is due to the pigment produced by the hyphae as it grows into the wood. Assuming you’ve thoroughly cleaned the wood, this staining is harmless and merely an aesthetic nuisance. Removing the staining requires sanding or heavy chemical usage, both of which will harm the finish of the wood. I only recommend trying to remove the staining if you plan on refinishing or repainting the piece of wood.
I gutted and remodeled our bathroom and ended up attaching a layer of green board to the sheetrock that was on the ceiling. I did not want to disturb the 14 inches of blown in insulation that was in the attic over the bathroom. Now, 23 months later (and 11 months since family moved back in that take HOT shower everyday in that bathroom) we are getting a mildew odor in the room. Can a double layer of sheetrock over a tub cause mildew/mold to grow between them?
It’s highly unlikely mold would grow in between the two layers of sheetrock. If condensation were to occur, it would appear on the surface closest to the warm, humid air (the green board in your case). Must odors are common in bathrooms with insufficient ventilation. I recommend installing a Panasonic WhisperGreen or wiring an automated timer switch to your existing fan.
In my bathroom, the light fixture is not working. So no light gets in at any time. I recently noticed a very musty smell, which is also throughout the house. I would like to know if my health is at stake. Thank you for your patience in reading this message.
The lack of light in the bathroom would not directly cause the mold growth. The main cause of mold on a bathroom ceiling is a broken or ineffective exhaust fan. I recommend replacing the fan with a constant flow unit such as the Panasonic WhisperGreen fan. Here is a link. If that’s outside of your budget, you can install a timer switch on the existing fan. Run it at least 12 hours/day in the cooler months.
What's this on my bathroom ceiling. I wiped it off and saw no opening. What should I do next?
This appears to be mushroom type of fungi. Typically these only grow in highly saturated materials, i.e. from a water leak as opposed to humidity. A mushroom growth on a ceiling is quite unusual. This type of fungi requires significant nutrients, which often come from soil or rotting wood.
I would thoroughly investigate the area above the ceiling and look for a water intrusion. A moisture meter would be very helpful for investigating the source and extent of the leak. See if you can rent one locally.
Can you identify what is causing this please?
It appears high levels of humidity are leading to extreme condensation on the ceiling and walls. If you live in a hot/humid climate, ensure your A/C is working correctly. If you live in a cool climate and this occurs in the winter, increase your ventilation dramatically. Run the bathroom exhaust fan 24/7. Monitor the relative humidity – your goal is to keep it below 50%.
Hi. We are looking into purchasing this home in VT. Sellers say this addition (lofted area above kitchen) was put on in 2007. No one has lived in the home for 3 years. They believe the mold was caused from high humidity and no dehumidifier. I’ve been researching and everything I read says not to use recessed lights on cathedral ceilings. There is a newer metal roof but I do not see any soffits or vents. The downstairs now has mold on the furniture and walls, but I can wipe it of with my hand. Any suggestions?! Thanks
The mold growth is quite heavy for humidity alone. It’s possible, but it would require an extraordinary amount of moisture – i.e. long term water leak below. It would be highly unusual for a vacant home to accumulate this much mold growth without an active water/roof leak.
One possibility is dripping from condensation in the roof assembly. An unvented metal roof with can lights below can become completely saturated. In severe cases, this can drip down onto the ceiling. Note, this would only occur in an occupied home. Either way, I recommend identifying the type of insulation they used. Also, make sure the can lights are AT (air tight) rated. Additionally, look for rubber gaskets on the trim rings. This case is significant enough to warrant a professional inspection.
A tree fell on my house recently and when we had builder go in the attic to do repairs they discovered mold. WE had the whole roof replaced and were getting a ventilation fan installed. When the mold people came out after the house roof was replaced, they said the mold had gotten worse! Some say its because we have a lot of fish tanks in the basement, and heat lamps for pets on the second floor. Others say its cause the roof is leaking, some say it’s because of a leaky pipe. How do I find the cause? is there a company that will determine the cause? I need to find out!
Fish tanks can be a major contributor to mold growth. They add a large amount of moisture to the indoor environment. Due to the stack effect, this moisture migrates upward through a home, and eventually into the attic. The heat lamps are not a problem. If you plan on keeping the fish tanks, ensure you have continuous exhaust ventilation on the top floor of the home. This can be accomplished with a constant flow fan such as the Panasonic WhisperGreen.
These issues are often due to a combination of factors. In your case, the roof might be under ventilated as well. Often a single vent fan is not sufficient. I recommend verifying that the entire roof is well ventilated. Check out our page on attic ventilation.