Getting foiled


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Old 07-29-06, 02:32 PM
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Getting foiled

In todays Sa 7-29-06 newspaper was James Dulley's column about foiling and ventilating an attic. He said he did his OWN, (the combination of foiling and venting) and claims that the temp in his bedroom went down 10 degrees!

Being the 'scientist' that I am...I would have liked to see him, or someone first do one or the other, and report on the temp drop, rather than doing two steps at once.

He calls the heat infiltration 'radiant heat'. He claims that the fiberglass insulation in the attic does not stop 'radiant heat'...that the insulation wil get warm.

How can it be radiant heat when there is no longer 'rays' radiating?

But whatever kind of heat it is...we know attics can get very hot... and if the attic is hot, the insulation is going to get hot. Insulation just slows the transfer between hot and cold. It does not stop it.

The foil gets stapled to the underside of the rafters with the shiny side down. Down. I wonder why down? He claims that the foil does NOT work on the principle of it bouncing the heat back up. Rather he says it is due to it's low-e (emissivity) factor. The top side is either kraft faced or meshed, he said. That is the most economical kind he said.

Now I am wondering about the theory behind how this works. What is there about the foil exactly? Especially from it pointing down. What would happen, in theory, if you had solid ridge and soffit venting and you were to let's say nail up plywood underneath, rather than the foil? Or what if in theory you screwed on 1/4 inch plate steel (not that you would, of course. I'm just wondering about the theory of this...of what there is about the foil, if it's not actually reflecting away the sun's rays..which obviously it's not, in the attic space.

I foiled my house windows...remember...and that is reflecting away the rays and stops the heat infiltration dead in it's tracks. HE claims that the foil in the attic gets hot...but that it do to the low-e, it does not llet, or slows. the heat from passing through.

Then he said that if you were to resheath your roof, you can even buy foil faced sheathing, so that the step of foiling is already done.
 
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Old 07-29-06, 03:32 PM
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What are you asking? Could you number your questions or something ?
 
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Old 07-29-06, 04:27 PM
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1. Has anyone else here done this? Any thoughts on it?

2. Does anyone else truly understand the principle on how this works exactly, with the foil pointed down?

3. What does foil really do when there isn't direct light shining on it? What is there about foil, as opposed to other materials, like plywood or plate steel, instead...in this case where the direct rays of the sun are not striking the foil?


..........................

Sorry.
 
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Old 07-30-06, 04:27 AM
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I'm considering doing something close. I was going to use styrofoam board with the foil face nailed to the underside of the rafters with continuous soffit and ridge venting. I would leave a space at the ridge for attic ventilation. I have read good and bad with doing this though.

My understanding about putting the foil face down is that while it isn't quite as efficient at first, over the long run it is better because it keeps the foil from getting dirty/dusty, which would limit its reflective action.
 
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Old 08-01-06, 06:08 PM
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Makes sense about the dust.

As far as for the venting..I wonder what is best?: To allow soffit vented air to enter and be forced to JUST go up the rafter spaces directly to the ridge venting? or, to have a gap at the attic flor to allow the air to also get inside the "A" (the whole main part of the attic) you create, and allow it to go up to the ridge venting from there? Dulley says to leave some gap (didn't say how much) at the attic floor, so maybe the air will go BOTH pathways: Some up the rafter channels and to the ridge vent, and some out into the attic space, and then up into the ridge vent.
 
 

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