Ceilings Dripping? You May Have Attic Frost

attic frost
Frost on truss run where bath vent came dislodged.

Got attic frost?

One of the most frequent calls we get in the dead of winter is that the customer’s ceiling is “raining” or “dripping” around ceiling light fixtures or ceiling vents.  This normally occurs after a period of deep cold followed by warmer temperatures causing frost to melt and “rain” or “drip” through the ceiling.  Homeowners may also see their walls “sweating” around windows that are not insulated/sealed properly.

There are two main reasons why attic frost occurs…

The first is from humidifier abuse.  No matter how you look at it, humidifiers make people feel good, but this is not the case for your house.  Humidifiers can put a gallon or more of water into your home every single day!  There is a reason insurance companies charge more for flood and water insurance.  Water causes the worst damage other than fire.  Would you pour a gallon of water into your attic every day?  This is exactly what happens when humidifiers are used.  The warm, moist air rises to the attic space through any gaps in the ceiling and walls and that moisture rises to the attic and freezes to the roof sheeting.

If a home is sealed and insulated properly, humidifiers running at recommended levels of no more than 15% should not normally cause a problem. However, many homeowners run their humidifiers at 30-50% humidity in an effort to beat the winter static electricity and bloody noses, and heck… to just feel more comfortable!  Keeping humidifiers as low as possible is the key to avoiding moisture problems in the home.  If you must use a humidifier, also consider a small bedside humidifier that is used only as needed.

attic frost
Vent tubes and bath vent disturbed.

The second reason for “raining” or “dripping” ceilings is from disturbed/too little insulation or if venting becomes disturbed in the attic.  This can occur if contractors must do work in the attic and trample down the insulation or possibly dislodge venting or can light fixtures.  If bath steam is exhausting directly to the attic space, it is like a drip hose on in the attic constantly.   You can imagine the kind of damage that can occur with a direct link from your bathroom steam to freezing air.  After the steam has frozen on the attic ceiling, it hangs out just waiting to wreak havoc when the temperatures rise above freezing, normally in the form of  “dripping/raining” ceilings or “sweating” walls.

It is important to keep attic insulation untouched after insulating to continue to enjoy the benefits of a properly insulated and ventilated attic.  If you must have work done in the attic, be sure to ask your contractors to take care in the attic space not to disturb insulation and venting.


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