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Old 07-11-2013, 01:46 PM   #1
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fiberglass in louisiana

in louisiana. i am currently remodelling a 1400 sq ft. home. roof is very low pitch. there is no attic space. all air cond. system will be inside conditioned space. the ceiling is composed of 2x6 rafters. roof is asphalt shingle already installed on roof deck (1x8 boards) that run perpendicular atop the 2x6 rafters.. there is no vapor barrier or air barrier other than roofing paper.

the space in between 2x6 rafters is completely unvented. no soffit or ridge vents. (i have read many pros and cons to this unvented vs. vented ceiling)

Question: i dont have alot of space. i would like to veer from spray foams. how should i install fiberglass batting. what type is best? do i need to add any type of vapor barriers against underside of roof deck etc. should there be space between batting and roofdeck. thanks


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Old 07-11-2013, 02:43 PM   #2
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Easiest solution would be the foam vent baffles and fiberglass insulation, then install foam board insulation and strapping on the bottom side of the rafters (thickness would depend on type of insulation and height of your ceilings).

Fiberglass is fiberglass, you can get it faced or unfaced. I don't consider the face to be much of a vapour barrier but it might make it easier to install. Your local building department should be able to give you direction on the vapour barrier question.


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Old 07-12-2013, 01:01 PM   #3
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that vapor retarder on fiberglass insulation SHOULD be considered as such as it is recognized as one within the building codes. It is typically a class II vapor retarder and given your zone is recommended at the exterior to minimize vapor drive during cooling seasons. Certain kinds of foam board (XPS and polyisocyanurate) are also considered a vapor retarder when installed in thicknesses over 1" for XPS (class II) and typically almost all polyiso as it is mainly sold with metal facings that classify it as a class I retarder. You should definately be visiting your building department as a misallocation of vapor control in your region can quickly turn into rot/mold issues.
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Old 07-13-2013, 08:12 PM   #4
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You are under the 2009 IBC;

In Zone 2 or 3;

You may need ventilation of the attic, check with local AHJ;

They may refer you to this, Exception #2;

If you are required to add ventilation , use the lower-1/300 and a vapor retarder (asphalt-faced batt) and no worries;

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Last edited by Gary in WA; 07-13-2013 at 08:15 PM.
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