High Humidity Attic

As planned the r 40 worth of insulation has drastically reduced his heating bill but now he faces another unexpected problem.

High humidity attic.

In contrast the humidity near the ridge in the attic gets very high. So compared to that hot humid attic the vapor pressure at the other side of the foam is a factor of six higher. If there is excessive moisture accumulation in your attic it will condense on cold areas mainly on the underside of your roof deck. Attic moisture usually appears because of condensation.

The dew point and rh get up close to 90 f and 90. At 140 f 80 humidity corresponds to 120 torr or 16 of atmospheric pressure. During the winter months the recommended relative humidity inside a house is anywhere between 30 50 percent. 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.

That s way too high. Jason advani has insulated his attic with spray polyurethane foam and while his heating bills have dropped high humidity remains a problem. The dew point and rh stay below 70 f and 70 at their peak the peak of humidity not the peak height in the attic. Attic temperature depends on the outside temperature and it also depends if your house is insulated.

By scott gibson march 18 2019. But the humidity near the attic floor never gets out of control. 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.