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Old 01-08-2012, 03:39 PM   #1
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I want to be sure


I'm closing on a purchase of a cabin in the mountains in East TN next week and am making plans to correct some issues. One of which is the crawlspace....it is damp, has moisture and isn't insulated properly -

Currently the Crawlspace - (Vented) has vents open and the fiberglass
insulation is falling out of the floor joist, less than 80% of
the ground is covered with vapor barrier.

Plan of attack - cover 100% of ground with 6 mil vapor barrier going 6"'s
up the wall, glue it to the block wall, replace the sagging
insulation between joist with fiberglass R-19 faced and have the
paper facing up toward the heated space, leaving the air gap at
the heated floor, then cover the complete floor with poly
insulated sheathing with the foil facing toward ground,
then tape all the joints to completely seal the floor joist cavity.

Still using the vents...closed in winter and open in the summer

I've read eveything I can find and I know there are mixed views on vented or unvented but as discribed does this sound good?

Thanks in advance for any input

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Old 01-08-2012, 04:16 PM   #2
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I want to be sure


If you are using faced insulation, what is the purpose of the air gap? You don't want two vapor barriers in the same insulation sytem. An air gap allows for convective currents which you don't want. You plan to place a foil faced board at the cold side and seal the seams which creates yet another vapor barrier. And foil is the most efficient so if any vapor is going to condense in the system it will happen right at the foil membrane. Poly on the ground is OK, but doesn't really do much in a vented crawl space.

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Old 01-08-2012, 04:34 PM   #3
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Change out your old style vents to automatic opening, there only about $17.00 a piece at Lowes or HD. In most cases I can change one out in less them 15 min. It opens when warm and closes when cold with no power, No way you can forget to open or close them.
I'll make a guess the area under you house is lower the the grade outside.
Unless you raise that grade by adding sand it will always be a swamp under there.
It's very important to have that 6 mil. vaper barrier. I live in a very low lying area and seem to have the same conditions as you.
Without that barrier the insulation will stay wet and fall down, also the insulation hangers will rust and fail.
And no there is no need for an air space between the floor and the insulation. You also do not want to form a double vaper barrier.
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Old 01-08-2012, 04:54 PM   #4
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R-13 won't fill the joist cavity and I mentioned the air gap at the top becasue one of the recommended sites posted it but it did not say if the insulation was faced or not which is why I asked the question.
I live in Alabama and the cabin is in TN and for some reason Lowes and HD in both cities only stock R-30 in unfaced insulation except for the Roxul which is over double standard insulation.....but if that is the only way it will work then I can do that.

So should I put the paper against the house floor? should I pull the paper off since it will have the poly sealing it in?

I agree on the auto vents and will plan on doing them once I get past some of the other projects.
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Old 01-08-2012, 05:08 PM   #5
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Here's the picture that I'm using as a guide

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Old 01-09-2012, 07:34 AM   #6
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Quote:
Originally Posted by gcan View Post
Here's the picture that I'm using as a guide

What is the point of the air gap in this application?

Where did you get the picture?
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Old 01-09-2012, 06:02 PM   #7
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Wow - not sure why the air gap...see the link below the picture I used is figure #7



http://www.buildingscience.com/docum...n-crawlspaces/

thanks for the help
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Old 01-09-2012, 07:17 PM   #8
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As the BSC article brought out, radiation heat transfer is stopped by the foil-facing.

Convective heat transfer is stopped by the seam-sealed foam board (high density).


That just leaves conduction = air gap to floor sheathing; http://www.buildingscience.com/docum...l-in-buildings


Tape all seams, it has to be air-tight....


Just be certain to foam board/canned foam the rims first, if no foam on exterior; http://www.buildingscience.com/docum...ce-insulation/

I would also partition the floor joist cavities over the bearing beams with foam board or the existing solid wood blocking and caulk to divide the floor space in to segments, in case of an air leak somewhere…


Gary
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Old 01-09-2012, 09:01 PM   #9
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will R-13 faced work in the floor cavities if I pull the paper off? unfaced for some reason is hard to find in my area, except R-30.

Using Roxul cost over 2X as much as kraft insulation.

In the rim cavity does the foil go toward the rim joist or face out to the crawl space?

Last edited by gcan; 01-09-2012 at 09:06 PM.
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Old 01-09-2012, 09:20 PM   #10
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R-19 for your area if in Zone #4: http://publicecodes.citation.com/ico...001_par001.htm

http://publicecodes.citation.com/ico..._11_sec002.htm

You should be fine with the R-13. The asphalt paper facing is a little iffy because your location doesn't warrant it. Zone 3, or 4? It is a vapor retarder, not barrier as some call it. It is moisture variable with wetness; http://www.buildingscience.com/docum...vapor-barriers
Just pull it off, if concerned, to be safe.

Good to cover the dirt with poly.

Gary
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Clothes taking longer to dry?
Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!
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Old 01-10-2012, 05:51 AM   #11
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Great - I up it to R-19 FG and pull the craft paper off


thank you for the response
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Old 01-11-2012, 10:40 AM   #12
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You're welcome, glad we could help!

Gary

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Clothes taking longer to dry?
Clean the dryer screen in HOT water if using fabric softener sheets.
They leave a residue that impedes air-flow, costing you money.
Clean the ducting in the last six months? 17,000 dryer fires annually!
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