Question for HVAC gurus.

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Hi guys. My wife and I are in the late planning stages of building our new home. I want it to be as energy efficient as possible. We are having a slight disagreement.
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?
Can anyone give me advice on why my thoughts are wrong?
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Alim Nassor wrote:

Are you going to use the attic for storage? Depending on where you live and the local climate, anything you store in the attic could be damaged by temperature extremes. I've seen some very large attics that were an incredible waste of space, is yours one of those?
TDD
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wrote:

Haven't planned on using it for storage. We will be building about 60 miles north of Dallas. That's why the though of semi conditioning that space sure seems wasteful. And we get pretty dang cold in the winter and I hate the thought of my warm air going through the ceiling into an attic that isn't used for much.
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Alim Nassor wrote:

Well insulated ceiling and temperature controlled ventilation for the attic may be the way to go.
TDD
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wrote:

My thoughts too. Thanks.
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You are right you will be heating the attic from migrating heat loss up, the builder will be happy to agree since it will take more foam, more foam means a bigger job, more money. If you are foaming everything you are including a heat recovery ventilator for that tight house.
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I hadn't explored the heat recovery ventilator. I'll need to research thst. Thanks
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Then You AC pro aint no pro because a fomed house is like living in a foam cooler, its doent breathe or have enough air exchanges per hour to keep you healthy, google overtight houses that dont breathe, sick house syndrome, do research now and maybe hire an architech because several ideas you plan dont make sense, maybe alot more dont.
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It was just a casual conversation with my wifes ex about the house, not a detailed planning session, he wont be the HVAC contractor. i'n just getting ideas.
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wrote:

It was just a casual conversation with my wifes ex about the house, not a detailed planning session, he wont be the HVAC contractor. i'n just getting ideas.
======================================================================================
I think the expression is Build it Tight, Ventilate it Right.....
I added glass wool insulation to the attic floor *and* roof joists, and what a difference!
Ahm no spert, but I think ventilating a tight house is not nearly as difficult as making it tight.
I'm reminded of an acquaintance up in Mass. who read something about "ventilated attics", and promptly hole sawed/sawzalled about 400 holes at the base and outside of her attic!!! Sure makes insulation moot, dudnit?????
I fought like crazy against this idea, to no avail. I don't know how she's doing with all those effing holes, but I did detect the onset of some grumbling.... Might as well just open all the windows in winter, while she's at it!.
You have winters in Dallas???? For how long, and how cold?
Oh, a note on attics:
If the attic is such that you can stand up in it and walk around, they can become pretty useful from a variety of povs. It helps to have a *good* drop-down staircase going up, and decent lighting. They can be neat work-spaces for light things like sewing, etc, made into neat play areas for kids, even serve as infrastructure for things like A/C, warehousing inventory for a home business, etc.
We added almost 1,000 useful sq ft to the house by just insulating, throwing down some plywood, and unrolling some cheap commercial carpet, adding some fluorescents along the apex. No heat necessary, not too bad in the summer. NYC area.
However, a fully finished attic(for living) likely violates code, or will require a permit.
--
EA






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I gotta go along with the others who say insulate the attic floor. From what I have heard, foaming the rafters (underside of the roof) can cause high humidity/condensation problems in the attic. I would use radiant barrier roof decking and plenty of attic ventilation. You can reach a point where slight gains in overall thermal efficiency can cause major side effects that offest any savings exponentially. Larry
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iirc, Silva on Ask TOH did a very inneresting ditty on insulation (esp. spray insulations) very recently, and goodgawd, does it get complicated! And it went by pretty fast, something you would def'ly want to take notes on.
For example, the vapor barrier goes on different sides, depending on yer climate. In mixed climates, there are additional "breathable" barriers you can use.
Would be useful to catch that episode, don't know if the TOL has it.
Seems to me a double-layered roof, with a 2-4" air gap, with continuously circulating air, and then the bottom layer super-insulated (anything/everything) on the attic side would be a permanent solution.
But I've never heard of a double-layered roof, which seems simple enough to do, just some extra plywood/2x4's.
I'm considering just living in a tent....
--
EA



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wrote:

Double layered roof is what you get when you put Spanish tiles on a roof. The air can flow under the tiles. You get the same effect more or less by putting foam insulation underneath the decking with an air space between the foam and decking.
Jimmie
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WTF, you allow her EX to put in his 2 cents! Thats your problem, ban him. Even worse, he is an AC contractor not contracting.
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wrote:

WTF, you allow her EX to put in his 2 cents! Thats your problem, ban him. Even worse, he is an AC contractor not contracting. ================================================== If he's anything like the cretins on alt.hvac, she's proly paying HIM alimony! Or at least giving him a beer allowance.....
--
EA



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Alim Nassor wrote:

1. Foam the underside of the roof? If you do that, the shingles will melt. Well, maybe not melt, but they will surely degrade rather quickly.
2. The almost unanimous advice, I'll bet, of the experts and knowledgeable amateurs here is that you will rue the day you go against the wishes of the lady of the house. Hereafter, EVERYTHING that goes wrong will be attributed to your hair-brained decision on the attic. I'm talking stopped-up toilets, mice in the pantry, windows that won't close, psoriasis, and the refusal of the grocery clerk to take coupons for stuff your wife didn't buy.
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Inneresting! How bout regular bats (glass wool) of insulation?
Proly doesn't apply to slate.
Suggests making a kind of double roof, for air flow beneath the shingles! Then the joist gap in the attic can be foamed.
--
EA




>
> 2. The almost unanimous advice, I'll bet, of the experts and knowledgeable
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My neighbor has a cathedial ceiling poorly vented with just regular insulation, his 35 years shingles only last 5-6 years in S. exposure, yup, heat kills and so do a wifes ex that you stupidly allow to get within 100 feet or give info on money decisions.
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Why is it in every newsgroup there is a guy who likes to throw insults around, and usually when he is talking about something he knows jack shit about?
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Alim Nassor wrote:

And why did you decide to come to this one?
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