Written by: carmstrong
Mold growth in attic
Attic vents covered during reroofing
Remove and replace affected portions of roof sheathing. Reroof with adequate ventilation.
When the homeowners had noticed dripping water and mold growth in the attic, they contacted SBSA for an evaluation of the cause and conditions.
Built in the 1970s, the original wood shake roof of the house had been recently replaced. SBSA performed the observation of the home on a clear and warm January day (65° F); the relative humidity outside the home was approximately 15%. Inside the attic, the relative humidity was as high as 67%.
At such a high relative humidity, the dew point—the temperature at which water condenses—was 54° F. When the temperature inside the attic got below 54° F, condensation formed and was causing the drips and mold that the homeowners reported. How did the attic get so humid?
Common household activities such as cooking, bathing, cleaning, and even breathing introduce water vapor into the air.
This water vapor permeates through holes and cracks in the ceiling and into the attic. The homeowners were not using humidifiers in the living space below, and the ventilation in the attic wasn’t adequate.
The attic ventilation had been sealed over when the new roof was installed, and no new ventilation was provided. Although the roof was not actually leaking, the vapor condensing on the inside left the roof sheathing dripping wet and mold was growing. Because this ventilation issue was detected within months of the roof replacement, structural damage to the wood framing was not yet an issue.
However, the roof sheathing needed to be replaced and extensive mold remediation of the framing was required. The brand new roof had to be removed and the roof rebuilt to include adequate ventilation. This example illustrates how changes that are meant to be improvements can actually create new, unintended problems.
SBSA can help prevent such unintended consequences through peer design review, effective new design, and construction quality assurance.