On Mar 6, 2:53*am, Wayne Whitney wrote:
On 2010-03-05, Alim Nassor wrote:

I want foam insualtion in walls and attic. *She is ok with that. *What
we disagree about is how to do the attic.

Her ex-husband is a HVAC contractor. *He says we should use the " foam
the underside of the roof, seal the attic and semi condition it"
method. *Our builder agrees.

My problem with that is, why would I want to semi condition an area
the same size as my house if I am never going to use it for anything?
I want to foam the attic floor, and make sure the attic is well
venitaled. *Why is allowing my warm and cold air (that I am paying *to
heat and cool) to migrate up into my attic a good idea? *Isn't it more
efficient to keep that expensive air in the house by well insulating
the attic floor?

Either method will work well if done properly. *Heat loss (in the
winter) or gain (in the summer) depends on the surface area of the
thermal envelope and insulation values. *The actual volume of the
conditioned space does not matter directly. *Since the roof is a
larger area than the ceiling, if you make the roof part of the thermal
envelope you will have somewhat more heat loss/gain, unless you
insulate it to a correspondingly higher R-value.

But it is not a large effect, and there can be good reasons to
condition the attic space. *For example, if your HVAC equipment will
be in the attic space, then there are advantages to having all the
ductwork in conditioned spaces.

As others have mentioned, if you do insulate the roof, then the roof
deck can get quite hot in the summer unless you take measures
otherwise. *Depending on the roofing material, this can be a problem
(e.g. with asphalt shingles). *But I believe you mentioned using a
galvanized metal roof; I don't think roof deck temperature would be an
issue for that material.

Cheers, Wayne

Thanks Wayne.