Chimney Sweating In Attic

The same thing can happen with your chimney.

Chimney sweating in attic.

Look for stains on the rafters close to the chimney as well as insulation with water damage on the attic floor. Sometimes a leak starts in a different place but finds its way to the chimney and then visibly enters the inside of a room at the point of the chimney. The new decking was mostly dry except for droplets of moisture apparently condensate not leakage from the roof on a few nails. When the warm air of the house comes into contact with the cold wall that separates the living space from the chimney water from the air will condense onto the wall s surface.

However the chimney was a different story. If there is excessive moisture accumulation in your attic it will condense on cold areas mainly on the underside of your roof deck. Condensation of exhaust gases are evidenced or accompanied by one or more of the following. The smaller amounts of heat which do go into the chimney are cooled by the surplus cold air and simply don t have the energy to make it to the top of the stack.

For example your roof might have a leak through the attic vent or roof shingle at the top. The pattern of wetness is relatively uniform on all the sides of the chimney exposed in the attic. Knowing which side water is coming in on is powerful information. The wetness on the outside faces of the chimney occurs when the condensate migrates through the mortar.

During the winter months the recommended relative humidity inside a house is anywhere between 30 50 percent. Normal amounts of humidity and moisture in the hot air condense inside your chimney as the air cools leaving water which can be as acidic as bleach. In the attic a kneewall blocked observation of the chimney. Staining on the exposed chimney in the attic often reveals which side of the chimney water begins its travel to other areas.

A flue that is too large allows too much air to circulate making it difficult for the warm gas and vapors exiting the furnace to create a strong updraft up and out of the vent. The sweating in this case is normal and will cease once a fire is built and the chimney heats up.