Vented attic vs. a sealed, non-vented, airtight attic
calwsmith
| Posted in Energy Efficiency and Durability on
I’m building a new home in Miami, Fla.
An insulation contractor advises me to eliminate the planned roof & soffit vents and seal the attic with foam.
What are the Pros and Cons for maintaining attiic ventilation, and eliminating it?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Calvin,
In a hot, humid climate, there is no advantage to inviting outdoor air into your attic. The hot, humid air belongs outdoors, and you need an air barrier between the hot, humid air and the interior of your house (as well as your attic).
This is especially true if you plan to install any ducts in your attic.
For more information on these issues, see:
Creating a Conditioned Attic
All About Attic Venting
Not only is there no advantage, it's a real DISADVANTAGE to go with vented attics in FL. It brings in far more moisture than it purges, and makes it more likely to lose the roof in a hurricane.
The Florida Solar Energy Center compiled a literature review of vented vs. unvented attics about a decade ago, looking at it from all different angles- it's worth a careful read:
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf
The bottom line is still the same: There is no good rationale for vented attics in Florida, and many reasons to avoid them.
Seems like your question was answered, but for others reading this in the future, I recently posted a similar question on a different site: http://ths.gardenweb.com/discussions/3313447/cons-of-building-an-upper-level-without-an-attic
Thank you all. I have read the FSEC's report and given consideration to your opinions. A plan revision is in process for a non-vented attic with sprayed insulation to the underside of the roof deck.