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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.) Airborne moisture.  2.)  Liquid moisture.  The former occurs 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.

heavy mold growth on ceiling 1024-350

Ceiling mold problems have several positive attributes.  First, for obvious reasons, ceiling problems are often identified quickly. This can prevent a minor roof leak from turning into a major mold remediation issue.  Second, because ceilings are unobstructed from the underside, dry out will occur quicker than in other locations.  However, there are many caveats to both of these scenarios.  But first, let’s look at ceiling construction.

Identify the cause.

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.

Mold on ceiling condensation_cr

Airborne:

  • Mold growth is worse at the perimeter of the room
  • The room is on the top floor
  • The attic is poorly insulated
  • Discoloration is light grey (ghosting)

Liquid / Roof leak:

Roof leak before mold growth on ceiling occurs.
  • 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.

Unusual scenarios

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

Ceiling mold problems

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.

Cross section of moldy ceiling

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.

Remediation.

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.

Project Report > Inspection of Water Damage to Ceiling

Inspection #: 202030

Reason for inspection:

  • A water leak from a unit on the 4th floor affected the ceiling of a unit on the 3rd floor. Client opened up the location and suspected mold growth.  A review of both units was requested with recommendations and a quote for remediation.

Unit 304:

Floor damage + Mold

  • A two sq/ft section of wet sheetrock remains where a drywall seam extends away from the wall. (see photos)
  • Water damaged building materials remain in ceiling cavity.
  • Minor amounts of visible mold growth was found inside the joist bay.  This was confirmed via direct sampling of the location.

Unit 404:

  • Significant amount of visible mold growth was found under the vinyl linoleum in the bathroom area only.
  • Visible mold growth was also observed inside an open wall cavity next to the bathtub.

Unit 404

  • Significant amount of visible mold growth was found under the vinyl linoleum in the bathroom area only.
  • Visible mold growth was also observed inside an open wall cavity next to the bathtub.
  • Visible mold growth was observed behind the baseboard on the wall between tub and door.
  • Several floor tiles were found to be loose in front of the tub.
  • Elevated moisture levels were only noted in the vinyl flooring and in the gypcrete. Once the vinyl flooring is removed, the gypcrete will dry out naturally, however is would be recommended to install a small space heater to allow for a much quicker dry out.
  • RH:44 % Temp: 65°F CO2: 502 ppm CO: 0 ppm

Got a question? Ask it here and we'll post the answer below

"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.