Environmental Issue & Sick Building Syndrome Blog

            Picture the glass of cold lemonade, filled with ice …..It is sitting out on your picnic table at your 4th of July family picnic. (That is a much better mental picture than a snow shovel anyway)

             The outside of the glass is covered with condensation. In fact, there is so much condensation that there are streams of drips of water running down from outside of the glass.

           Please forgive the mental picture. I am not trying to torture you with thoughts about a hot humid summer during the freeze that is stretching from our California franchises up to our locations in New England. I am really talking about what is happening in the outside walls and attics of a home in cold weather.

           With my “Mr. Science” hat on, we are talking about condensation, which is the result of temperature differences and humidity. If you go up into your attic on a bitter cold day, you are likely to see icicles hanging from the nails in the attic and frost on the roof sheathing (sheathing is the wood you see when you look upward in the attic)

          The warm air of the house where we breath, sweat, shower and cook is moist. There may even be a few water leaks. The water vapor laden air travels upward until it hits a cold surface and then condenses on the surface. The attic sheathing frost is a result of that water vapor freezing. The icicles hanging on nails happens because metal fasteners conduct the cold from the exterior more readily than the wood, so, more airborne moisture collects on the nails than the wood. (a glass with 10 ice cubes has more condensate on the outside than a glass with 1 ice cube.

           That wet wood from condensation is the water source that can start mold growing in your attic over the winter. Those same science principles can result in interior moisture being trapped inside the hidden areas of the walls of a house, particularly in the walls of finished basements.

            When the water condenses instead of just passing through wall cavities and exposed surfaces, the water soaks the wood, paper on drywall and any other available surface that will grow mold.

            Now let’s talk about that same glass of ice water in the arid desert. You will not have condensate……… even on the 4th of July.  Low humidity=low amount of water vapor available to condensate

The lesson…………We need moisture/humidity control in attics, even in winter.  Many of our clients that have mold issues had stopped running their dehumidifier in winter because they did not think it mattered. OR…they turned their furnace humidifier to a high humidity setting.


High humidity can be a source of mold even in winter! Be careful to dehumidify your home to 45% relative humidity….even in winter. 

Posted by Dan Howard on January 6th, 2017 9:06 PM



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