Various changes can occur over the years which decrease the circulation of fresh air in the attic space. The addition of more insulation and/or the application of a new roof can adversely affect the ventilation in older attics.

Lack of ventilation causes the buildup of heat and the condensation of moisture. This promotes mold, rot and deterioration of the structure. It also accelerates the aging of the roof that can result in premature failure.

The amount of ventilation required by building codes is one square foot of vent area for each 150 square feet of attic floor area. Keep in mind that this is a minimum requirement. Unique or special circumstances can often dictate the need for additional ventilation. In order to promote the circulation of fresh air in the attic, it is necessary that cool replacement air be allowed to enter the lower portion of the attic near the eaves. The installation of a power vent to increase the ventilation in the attic area is sometimes advantageous.

Problems can arise when installing additional insulation in the attic areas. Care should be taken to prevent blockage of the soffit vents. Additional problems can arise with the installation of blanket insulation that has an attached vapor barrier. If the vapor barrier is reversed or placed on top of existing loose insulation, moisture can condense and be trapped under the vapor barrier. This can often cause mildew, mold, rot and decay. Once mold and mildew begin to spread, they become more difficult to control.

As always, if doubts or additional concerns arise, take the time to consult an authority.