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Ron Beard CCS
Senior Member
Username: rm_beard_ccs

Post Number: 55
Registered: 10-2002
Posted on Friday, March 18, 2005 - 03:49 pm:   Edit PostDelete PostPrint Post

This message is directed to those in the Florida [or other southern] areas.

I just returned from a visit to Florida [hey, who says you’re too old to enjoy Disney World]. While there I saw the vast majority of the newer houses with “off-ridge” attic vents ranging in length from 3' to 8' in length. I saw very few ridge vents. But almost all houses had continuous soffit vents. A large percentage of the houses have hip roofs.

Can anyone tell this northerner why this is so [we have been indoctrinated in the use of complementing soffit-ridge venting]? Is it that the amount air flow of the shortened ridge vent for the hip roof and needs the extra vent area; or is it because of hurricane winds across the ridge? Or some other reason - like it is cheaper for the builder to install?

Ron
Anonymous
 
Posted on Friday, March 18, 2005 - 04:27 pm:   Edit PostDelete PostPrint Post

Vented attics in the South are No. 10 on the list of Top Ten Dumb Things to do in the South - by Dr. Joe Lstiburek of Building Science:

http://www.buildingscience.com/topten/south.htm

anon
J. Peter Jordan
Senior Member
Username: jpjordan

Post Number: 48
Registered: 05-2004
Posted on Tuesday, March 22, 2005 - 01:16 pm:   Edit PostDelete PostPrint Post

It is difficult to make hard and fast rules about construction "in the South." I have frequently observed that "I lived 4 years in Atlanta and I never want to live that far north again--in fact I had to move to Hawaii for 19 years to get that cold climate out of my system." For me, I-10 represents the true Mason-Dixon line although I am almost ashamed to admit that I recently purchased a home about 2-miles north of I-10.

Projects designed for the Blue Ridge Mountains in Virginia should be approached differently from those designed for the coastal prairie of Texas, and I think I can say that a building designed for a coastal condition in New Jersey may have more in common with a building designed for Galveston than it does for a building designed in Wilkes-Barre, PA.

Vented attics will make more sense where design is based on natural ventilation, most desireable for coastal regions in the South. They will also make more sense where there is good ventilation, not just a few soffit vents. Getting a good HVAC person to seriously evaluate this is difficult even in a commercial project. We did a project a few years back where we had a metal hipped roof with thermal insulation at the ceiling. After a number of meetings where the MEP consultant was directed to look at this, he finally realized that we had designed a pizza oven (roof color was dark green to add to the heat gain), and maybe he had better provide some mechanical ventilation for the 20 to 25,000 square feet of attic space.

Sometimes you have to look a specific cases before you blindly follow a rule of thumb.
Anonymous
 
Posted on Tuesday, March 22, 2005 - 01:56 pm:   Edit PostDelete PostPrint Post

Lstiburek's recommendations are based on the laws of physics, and are not merely "rules of thumb."

Definitions of climate zones are provided, on the web site, to guide designers through the recommendations for each.

The example cited in the original post falls into the "Hot-Humid" category. There is a definition of this climate zone as well as building case studies for several Hot-Humid locations in the US:

http://www.buildingscience.com/housesthatwork/hothumid/default.htm

Attic venting is DUMB in this climate for all the reasons stated on the Building Science web site (assuming that the building is air conditioned).

anon

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