Unvented Attics In Hot Humid Climates

2 unvented semi conditioned attics.

Unvented attics in hot humid climates. As home energy readers know venting attics in hot humid climates brings a great deal of moisture into the structure see conditioned attics save energy in hot climates he may june 97 p. In predominantly hot humid climates attics sealed to outside air exchange would correct this problem. If the attic is at 80 f and 80 humidity that s about a 21 torr vapor pressure of water. This facilitates the design of unvented attics in warm and mixed climates without an additional vapor retarder but requires an additional vapor retarder element in colder regions.

Even when outside air is hot and humid if the attic space is air sealed from the interior it is much hotter than outside air. The purpose of this report is to summarize and discuss the individual document references. Field issues related to spray foam unvented attics in hot humid climate zones such as moisture accumulation and indoor air quality concerns. What is less well understood is that venting causes many problems in cold dry climates as well.

High humidity in the attic insulating the underside of the roof deck solves one problem and creates another. In hot humid climates condensation on ductwork and air handlers located in vented attics is common. In this video i m reviewing all the reasons you should build conditioned attics in hot humid climates. Humid climates as it prevents.

I m joined by john umphress of the austin energy green. Advani is adding moisture to the air with a humidifier and that hot air rises finding ways of getting into the attic sullivan says. Fibrous insulation e g batt or blown in can be installed under the roof deck in the hot dry climate zone but this will cause moisture problems in all other climates straube and grin 2010. In modern residences the challenge of achieving a continuous air infiltration barrier and thermal insulation barrier at the interior ceiling level is especially difficult.

Report focusing on the performance and durability of unvented cathedralized attics in hot humid climates with both. If an r 80 unvented cathedralized attic is to be constructed in a cold climate it is recommended that a minimum of r 40 50 be air impermeable insulation installed and layered according to section r806 5 of the 2012 irc. Ductwork interior to thermal and pressure boundary duct leakage does not result in infiltration or exfiltration air change as ductwork is located within the conditioned space. So compared to that hot humid attic the vapor pressure at the other side of the foam is a factor of six higher.

Insulation approaches for unvented attics vary by climate. At 140 f 80 humidity corresponds to 120 torr or 16 of atmospheric pressure.