High Humidity Attic

If you have high temperatures and high humidity in your attic then you may also have a problem with mold.

High humidity attic.

Ventilation is another key factor. That s way too high. During the winter months the recommended relative humidity inside a house is anywhere between 30 50 percent. Jason advani has insulated his attic with spray polyurethane foam and while his heating bills have dropped high humidity remains a problem.

If there is excessive moisture accumulation in your attic it will condense on cold areas mainly on the underside of your roof deck. If the attic is at 80 f and 80 humidity that s about a 21 torr vapor pressure of water. The dew point and rh get up close to 90 f and 90. In contrast the humidity near the ridge in the attic gets very high.

As planned the r 40 worth of insulation has drastically reduced his heating bill but now he faces another unexpected problem. Attic temperature depends on the outside temperature and it also depends if your house is insulated. Jason advani jason advani thought he was on the right track when he insulated the bottom of the roof deck in his walk up attic with closed cell spray foam. Freezing and excessively hot outdoor temperatures rain and high exterior humidity levels make it difficult for your attic fan and heating and cooling systems to keep up with desirable attic.

Attic moisture usually appears because of condensation. At 140 f 80 humidity corresponds to 120 torr or 16 of atmospheric pressure. So compared to that hot humid attic the vapor pressure at the other side of the foam is a factor of six higher.