Vent vs Unvent attic
KevinChan02169
| Posted in General Questions on
Hi Guys,
I’m building a entire 2nd floor addition in zone 5, the plan from the architect call for a vent attic. I plan to run the HAVC ducts in the attic, should I go with a unvented attic in this case? My hers rater recommend using spray foam on the rater, and a continues bathroom fan install in the attic to take care the moisture problem. If I use spray foam, would open cell be ok? The open cell spray foam will be protect by fire retardant paint.
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Replies
The classic answer is a sealed & conditioned attic or plenum truss. But attic ducts can be well sealed and foam encapsulated - meeting the DOE Zero Energy Ready Home program requirement that ducts be installed in conditioned space.
Open cell is OK with a properly conditioned attic (warm and dry, like the rest of the house) and a vapor retarder:
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-016-ping-pong-water-and-chemical-engineer
https://www.finehomebuilding.com/2011/07/14/a-crash-course-in-roof-venting