Insulation and venting

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I'm to the point that I have to insulate on top and close the gables. I'm getting conflicting sides on where to insulate [ on top of ceiling or under roof deck] Wheather or not to vent the attic. There will be no duct work up there. It will be closed off.
This is a ICF house.
I was thinking of having spray foam applied to the top of the ceiling sheet rock thus sealing the living space completely like a igloo cooler. HAve been reading about not venting the attic area but am concerned with condensation. Metal roof installed.
I have not covered the gables yet so gable vents will not be a problem.
So the questions are
1] where do I insulate?
2] vent or no vent
I hope to get back up the middle of this month. Will take me about 5-10 days work then I can get living in this baby!
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Proper roof inuslation in some areas of the country is an important factor concerning condensation. In our area, the north pacific coastal area, I insulate above the ceiling, and provide venting at each end in the gable or with a ridge vent and bird holes in the blocking @ the plate. With the new fire safey regulations this blocking has been eliminated.....
I have worked on houses where the insulation was installed in each rafter bay with no venting and the owner complains of a roof leak..... The roof was not leaking rather condensing and dripping into the room. The plywood was rotted @ 2' down from the ridge....... I had to retrofit, provide venting and re-roof. jloomis

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mawillif had written this in response to http://www.thestuccocompany.com/construction/Re-Insulation-and-venting-15475-.htm : I am wanting to put fiberglass insulation in my attic myself. I was originally going to use Kraft Faced Fiberglass Insulation...with the faced side against the heated ceiling and just placed inbetween the joists. However, I am really worried about the fire-hazard aspect of using faced insulation. What does the warning mean exactly when it says to not leave exposed? Does this mean I have to lay drywall over all the joists to cover the insulation? Is the benefit of having a vapor barrier worth the fire hazard risk? Thank you.
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On Mon, 14 Sep 2009 14:57:10 +0000, mawillif_at_gmail_dot snipped-for-privacy@foo.com (mawillif) wrote:

Installing it that way won't give you a vapor barrier. I'd assume you are saying you have *no* insulation there now, and are going to install some. Just get non-faced insulation and you should be OK. Or get foil backed to reflect radiant heat, but as for the concept of a vapor barrier, that's meaningless at this stage.

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According to the code here in Oregon the kraft facing MUST go against the drywall ceiling panel. There's no additional fire risk since the drywall panel has paper covering anyway. This means, however, that you have to strip off the kraft insulation facing if you're going to have any "dropped" ceiling areas (like we had in our kitchen for soffit lights) The kraft facing can't be hanging out in mid-air or there might be a fire risk.
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on 9/14/2009 10:57 AM (ET) mawillif wrote the following:

http://www.thestuccocompany.com/construction/Re-Insulation-and-venting-15475-.htm
If you are putting the paper facing down between the joists and against the ceiling sheetrock, it is not exposed.
--

Bill
In Hamptonburgh, NY
  Click to see the full signature.
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On Fri, 24 Oct 2008 06:03:25 -0700 (PDT), Raider Bill

Top of ceiling, never the roof deck unless you make provisions to ventilate the space between the insulation and the actual decking.

Spray foam? I'd conside blow in cellouse insulation myuself.

You want venting. Do not block or obstruct the vents.

IMHO, ceiling

IMHO, vent.

Where is this house? That is a major factor in the decision.
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If attic is unheated it must be vented or you will mold then rot all wood. The attic floor is insulated. ICf so what is on floor now and R value, what is wall R value, what Zone are you? Foam attic floor to R 50-60 or more for Zone 5. Fiberglass looses efectivness as it gets real cold
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I think your intuitions are correct - spray foam to the top of the sheetrock of the ceiling below, sealing the envelope of the house as best as possible. this has several positive consequences. Use high density spray foam, as the low density foam is not an effective vapor retarder. As others noted, where you live is an important consideration.
- puts the insulation where you need it. since there's no attic mounted utilities, there's no reason to keep the attic in the conditioned space of the house. - blocks moisture movement into the attic - blocks air movement through the walls, at the top plate, wire penetrations, etc. - can provide good insulation value
I've been evaluating a lot of homes, and given what I've seen, I would definitely foam that boundary. IMHO, the attic/living space boundary is one of the most important ones in the house to seal tightly. I have never seen construction tight enough to block all air and moisture movement through walls, at joints, etc.Assume that the house is built leaky and foam the heck out of it.
Where my opinion diverges from the foam guys is I still believe in super insulating the ceiling. Most foam guys will tell you that you need less foam R value than fiberglass because foam is a more effective insulation. That's true to a point. However, using enough foam to fully coat the framing is beneficial to reduce thermal bridging and increase the true overall R-value. If you want to save a little, spray 3"-4" of foam then add a foot of cellulose on top of that, giving a total R-value of about 60. In hot climates, this will keep the rooms below the attic cool on hot, sunny days (assuming you do your windows and walls properly). In cold climates, it will keep them warmer.
As for venting - if you seal the attic with foam, there's no place for moisture to migrate into the space, so venting becomes far less important. The reason people get moisture problems in the attic is that they've got leaky construction that allows warm moist air from inside the house to migrate up there during the winter. Usually this is exacerbated by central humidifiers that dump too much moisture into the living space. A tight house shouldn't require added humidity. with that said, many building codes are requiring vented attics, so let them vent. Most of the time, they don't vent it properly anyway because almost nobody measures the "net free area' of the soffit vents and matches that to the ridge vent, so it's all for show.
If you're in a cold climate, keep in mind that soffit vents on the south side of the house can cause ice dams. Some building science studies have shown that the warm air rising off the south wall, heated by the days sun, can travel up the wall, through the soffit and heat the underside of the roof deck, leading to major ice dams.
See: http://www.cor-a-vent.com / for great information on attic venting.

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Foam guys lie, at least they have to me telling me foam is really R14, I think its to sell a job since foam is expensive.
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Dont know where the house is, but here in Texas, South East Texas, I dont go hog wild with the foam, house and the attic needs to breath, if you seal one up that tight, think of a fresh air return added to your HVAC system, to positive presure the house, and get some fresh outside air in there, cause we dont live in our refridgetors, we keep food in them. but to seal up so tight is not the best way to go, when I say not best way, I am talking healthy way as well.

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FYI, I happen to know the house is in Tennessee.
wrote in message snip
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Doug is right Athens. tenn.Good memory!
Sorry I posted and ran I'm back up here and internet and cell is very spotty at best.
I'm freezing my butt off. Icf sure is a great insulater as it has retained all the cold.
I like the idea of foaming the ceiling then blowing in some cellouse on tp.
But what about condensation in the summer from the the metal roof?
To vent or not to vent....... that is the question?
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On Tue, 28 Oct 2008 07:00:19 -0700 (PDT), Raider Bill

That question was answered by almost everyone-- you *must* vent. Period, not two ways about it.
Now, why do you feel you need foam? Why not just cellouse?
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Loose fill cellulose does nothing to stop air/moisture movement from the living space up to the attic - the primary source of problems with winter moisture buildup in attics. 2-3" of high density spray foam seals everything up, greatly, greatly reducing the opportunity for moisture to get into the attic and drastically reduce the chance for any moisture damage up there during the winter.
During the summer, the moisture drive is from the outside air. The metal roof cools rapidly and condensation forms under it if there is any moisture between the metal roof and the underlying sheathing so there must be a moisture impervious layer between the metal roof and the sheathing as well as room for ventilation between the metal and the sheathing to avoid moisture entrapment.
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Even a 1/4 inch of foam or sheet plastic works, a better reason is fiberglass and cellulose loose R value as it gets very cold, near 0 it might be 20% less R value. Fiberglass and cellulose settle easily 10%. But many foams can go bad and deteriorate if not painted
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All foams are somewhat vapor permeable. 1/4" of foam, even high density polyurethane, is quite permeable. Perm rating is non-linear. At 1", it is 2.6. A thin coat would block bulk air movement however, which would be good for most houses and could be a compromise. But better to use at least 3" everywhere. See: http://www.fomo.com/resources/technical-bulletins/Moisture-Vapor-Transmission.aspx
Cellulose increases R-value with decreasing temperatures: http://www.foam-tech.com/theory/rvaluedrift.htm
Settling not such a problem with cellulose as thermal performance doesn't vary much with density as it does with fiberglass. It will still decrease, but not a big deal since you applying lots of it - 12-15" typically ..
Foams only go bad if exposed to UV. Not much UV gets through shingles and roofs :-)
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Uffi foam once banned and now back in some use turns to powder in sealed walls, Have foams been around long enough to really know what will happen?
Cellulose that I have seen disentegrates over years, its just newspaper, and any roof leak makes it worthless, Cellolose settles is alot.
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Contrary to popular belief, modern, properly installed cellulose insulation does not settle.
s
Cellulose increases R-value with decreasing temperatures: http://www.foam-tech.com/theory/rvaluedrift.htm
Settling not such a problem with cellulose as thermal performance doesn't vary much with density as it does with fiberglass. It will still decrease, but not a big deal since you applying lots of it - 12-15" typically ..
Foams only go bad if exposed to UV. Not much UV gets through shingles and roofs :-)
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On Nov 2, 8:30am, "Steve Barker DLT"

Expain why, even fiberglass batts settle mine did, its like saying water doesnt evaporate.
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