Get in the attic to diagnose that leaky bathroom fan

Aug 09, 2023

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Question: Hello Ari, I am seeking advice on how to fix a recurring problem in one of my bathrooms. I have been in this 1952 home for 13 years and have had this same problem of seepage around the overhead fan when melting weather occurs. I had the fan installed about 12 years ago when I had the roof re-shingled. It has been supposedly fixed by various handy people over the ensuing years, as the problem areas were sanded down and repainted. I had hoped that the person that came last year had permanently fixed it, by adding more sealant around the vent on the roof last summer, but the same bubbling in the ceiling is occurring now. Apparently, it is not due to ice damming, as my insurance adjuster went into the attic last year about this time and he said that wasn’t the issue. Although, he did find a block of ice sitting on top of the insulation. He gave me the name of the handy person that I used last year, who unfortunately, didn’t resolve the matter with the sealant. Can you advise? Thanks, and I look forward to hearing from you.

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Question: Hello Ari, I am seeking advice on how to fix a recurring problem in one of my bathrooms. I have been in this 1952 home for 13 years and have had this same problem of seepage around the overhead fan when melting weather occurs. I had the fan installed about 12 years ago when I had the roof re-shingled. It has been supposedly fixed by various handy people over the ensuing years, as the problem areas were sanded down and repainted. I had hoped that the person that came last year had permanently fixed it, by adding more sealant around the vent on the roof last summer, but the same bubbling in the ceiling is occurring now. Apparently, it is not due to ice damming, as my insurance adjuster went into the attic last year about this time and he said that wasn’t the issue. Although, he did find a block of ice sitting on top of the insulation. He gave me the name of the handy person that I used last year, who unfortunately, didn’t resolve the matter with the sealant. Can you advise? Thanks, and I look forward to hearing from you.

Ruth K.

Answer: Determining the cause of leakage at a bathroom ceiling exhaust fan may only be properly accomplished when it is leaking. Looking in the attic and on the roof when the leakage is occurring should yield the answer and allow proper methods for remediation to be employed.

Leakage at bathroom ceiling exhaust fans is a very common occurrence, primarily in those which protrude into an attic space above. It can be somewhat tricky to install the three main components without some defects, which will usually cause a moisture related issue. Because bathroom fans are expelling very humid, warm air from showers and baths, problems with moisture intrusion are highly likely. We will look at the three points of potential problems individually to help solve your dilemma.

The first and most obvious location for leakage is the roof-mounted vent hood. Anything that protrudes through an asphalt shingled roof may be a problem for future leakage, even if it is properly installed in the first place. Most vent hoods have an angled or curved top, which prevents rain and snow from entering the duct connected to the fan housing. These may be effective against normal rain and snow accumulating on the roof, but may not be fully leakproof. In a driving rain, especially from a specific direction, some moisture may penetrate the hood. There is normally a damper inside the hood that prevents this, but strong winds can slightly lift this flap, allowing a small amount of rain to enter. If the fan is not in use when this happens, the rainwater may drip down the duct and enter the fan housing through the lower damper. This type of leak is usually minor, and should drain through the fan, saving the surrounding ceiling from damage. A similar effect may occur if the damper is forced open by wind-blown snow, or ice buildup. This problem should be fairly easy to diagnosed, at it will only occur during periods of precipitation, often with a wind from a specific direction.

The other roof related issue is if the shingles are not well sealed above or below the vent hood. This may occur with newly installed shingles, before the self-seal strips are melted in place, or when they deteriorate and ice damming around the hood forces them upwards. Both of these may be more difficult to pinpoint, as an inspection from the roof will normally be required to check for physical damage to the shingles. This will require an experienced roofer, who should be able to fix the issue at the same time, as long as the roofing is not worn out. This may also be partially investigated with a look inside the attic, to see if water is dripping down from the roof sheathing in the area surrounding the vent hood and fan duct. This may be possible by looking from the attic access hatch, or may require entering the attic and carefully crawling to the location when ceiling damage or actual leakage is observed.

The second area of concern is in the fan ducting, itself. This pipe may vary in location, length and angle, from short with a straight vertical rise, to very lengthy with several twists and turns. The shorter it is, the easier it will be to manage. It also has to be well insulated, often with pre-made corrugated plastic piping surrounded with fibreglass insulation and plastic sheathing. If this pipe is smooth metal, it will be more subject to heat loss and will require even better insulation and air sealing to prevent problems. A proper inspection of this duct will require a trip into the attic and checking for frost accumulation during cold weather and/or water-logging when the attic is warmer. Both of these may be signs of excessive condensation during the heating season and replacement and better insulation methods may be warranted.

The last issue, which is lesser known, is proper air sealing of the exhaust fan housing inside the attic. Too often this fan is installed and covered with a minimal amount of loose insulation, or a batt or two of fibreglass, by the initial installer. In a better scenario, the fan housing is covered with a thin layer of 6MIL poly, like the rest of the attic floor, before the insulation. That may work well, but only if the poly is properly sealed to the surrounding membrane. Either way, if warm bathroom air can leak into the attic from around or through the fan housing, it will likely cause moisture damage. It may wet the insulation as it cools and condenses, or rise to the roof sheathing above and form frost during the winter. This will surely melt the following spring and leak onto the ceiling or into the bathroom. Checking for proper air sealing techniques, or spring wetness and leakage, may be done only from a further visit into the attic.

In many homes, bathroom ceiling fan moisture damage can only be properly evaluated when the damage has already occurred and the leakage is active. This will certainly require a look inside the attic, but may also require remediation both in the insulated space and rooftop, as well.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

[email protected]

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