Condensation on metal roofs can be a problem once the weather starts to get cold. It can lead to roof leaks, even if rain has not occurred for several days. Condensation happens when moisture-filled air contacts anything that is below the dew point temperature. Metal gets cold faster than other items so condensation begins on metal first. This moisture can come from many things in a house including humidifiers, showers and laundry. Fixing the condensation problem on a metal roof can be accomplished with minimal difficulty.
Inspect the house by looking for vents that flow into the attic, such as bathroom and kitchen exhaust fans. Make sure they are venting out of the house and not into the attic.
Check for short circuits that may be causing moisture such as ceiling fans, unsealed light fixtures and vent pipes, and either eliminate the use of those items or repair them.
Line the attic ceiling with a plastic vapor barrier. This roll of plastic will help keep the moisture from leaving the attic. Roll out the vapor barrier and cut it to size with a utility knife to fit over the ceiling. Tape it all the way around with duct tape so it is secure and make sure there are no gaps or seams for any moisture to get through.
Check to see that the attic is properly ventilated and the warm, moist air on the inside can easily be replaced by cold air on the outside. Move all insulation that is blocking the path of the ventilation along the exterior wall of the attic to help ventilate the area.
Inspect your roof to make sure the metal has been installed over a felt underlayment and the underlayment is on top of plywood. The roll of felt is spread out over the entire roof on top of the plywood and nailed down with roofing nails. Insert a nail every six inches along the perimeter of the felt and every foot on the inside to secure it to the plywood. This plywood will absorb the moisture and prevent condensation.