What is an unvented attic all about?

The standard in building has always been to provide one square foot of attic venting for every three hundred feet of attic volume. The purpose of the attic venting was to remove moisture from the attic. When this code requirement was put in place the bathrooms and kitchens on most houses were vented directly into the attic pushing the moisture from the house into the attic.
Today all bathroom, kitchen and laundry rooms must be vented directly to the outside. We no longer push the moisture into the attic. As a result the only way to get moisture into the attic is through the attic venting. Testing across the country now shows that more moisture enters the attic during the cooler parts of the day than is expelled during the warmer parts of the day. This results in condensation on the HVAC ducts, duct hanger and piping. Since this moisture is not expelled it sets the stage for mold and mildew along with wood rot. Many areas of the country decided that the solution was to increase the size of the attic venting. When the attics were vented at one square foot per one hundred and fifty square foot of volume the problem got worse. Venting of attics is not the solution.

Creating an unvented attic is not possible using air permeable types of insulation. The air that passes through the insulation contains moisture and this moisture condensates any where the temperature is below the dew point. This is usually the underside of the roof sheathing. Using an air impermeable insulation solves the problem. Spray Foam Insulation is an air seal that does not allow moisture laden air to pass through it. It can be applied directly to the underside of the roof sheathing and to the gable ends creating an unvented attic assembly. These Assemblies are ICC approved in all areas of the country.

What are the advantages of an unvented attic?

1) They do not allow moisture to condensate in the attic
2) They keep the attic temperature within 5 to 8 degrees of the building
temperature.
3) The ducts of the HVAC are now not subject to the extreme attic temperatures which reduces the load on the HVAC by 20 to 30 percent saving energy.
4) In the event of a fire in the area the vents do not work like a chimney
and draw floating embers into the attic.
5) Wind blown rain cannot enter the attic.
6) Pests, birds, dust and pollen do not enter the attic.


For additional information please contact George Chittenden with Spray Foam Energy Solutions at george@sprayfoam.biz
www.sprayfoam.biz