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  1. #1
    Join Date
    Mar 2007
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    Austin, TX
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    Default Rafter Insulation

    Never a dull moment in this business. This is a 1 yr old remodel of a 1940's home. No attic insulation at the ceiling, instead they put up a 6" fiberglass batt insulation between all the rafters and no visible signs of ventilation noted anywhere. The owner stated the work was done by a rated Energy Star compliant contractor to meet the "new energy star rating standards".

    No insulation anywhere except at the rafters. Lots of attic storage, so it was difficult to get around.

    Seems like there will be lots of condensation between the insulation and the metal roof above all that insulation. Anyone run into this type of insulation job before?

    I'm not sure how to write it up other than it does not appear to conform to current building standards. Ideas?

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  2. #2
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    Default Re: Rafter Insulation

    Ken,

    If the attic vents have all been closed off and the attic sealed all around the perimeter (soffit, rakes, fascia, etc.) then that is an acceptable method. The insulation does not need to be the sprayed on foam typically found when a vented attic is converted to a sealed attic, the foam is just more common.

    I would be concerned about the insulation falling away from contact with the roof sheathing, was there any method employed to keep the insulation all the way up against the roof sheathing?

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  3. #3
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    Default Re: Rafter Insulation

    Hard to see in the photos but they did install a fine mesh netting material over the insulation at each of the rafters. It was not possible to determine if any vapor barriers were installed under the plywood decking that ran through the attic.

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  4. #4
    George Chittenden's Avatar
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    Default Re: Rafter Insulation

    Ken, I disagree with the other post. The only product approved in an unvented attic is spray foam. The reason for this is the spray foam is an air seal, it is not permeable so moisture does not pass through the spray foam and reach the sheathing. The sheathing is the concern because that is the area that will be below or equal to the dew point and allow for condensation. Fiberglass is very air permeable and so moisture laden air can reach the sheathing and condensate.

    I have seen a number of do-it-yourselfers who have done this. If you look at the other side of the fiberglass you will find the fiberglass is black with mold from the condensation.

    The ICC has never issued an ESR for unvented attics using fiberglass, They require venting to remove the moisture. The only other option would be a continous vapor barrier below the fiberglass to make the assembly moistureproof.

    This is a very bad idea.


  5. #5
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    Default Re: Rafter Insulation

    Quote Originally Posted by Jerry Peck View Post
    The insulation does not need to be the sprayed on foam typically found when a vented attic is converted to a sealed attic, the foam is just more common.
    Quote Originally Posted by George Chittenden View Post
    Ken, I disagree with the other post. The only product approved in an unvented attic is spray foam. The reason for this is the spray foam is an air seal, it is not permeable so moisture does not pass through the spray foam and reach the sheathing.

    George,

    From the 2006 IRC. (underlining is mine)
    - R806.4 Conditioned attic assemblies. Unvented conditioned attic assemblies (spaces between the ceiling joists of the top story and the roof rafters) are permitted under the following conditions:
    - - 1. No interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly.
    - - 2. An air-impermeable insulation is applied in direct contact to the underside/interior of the structural roof deck. “Air-impermeable” shall be defined by ASTM E 283.
    - - - Exception: In Zones 2B and 3B, insulation is not required to be air impermeable.
    - - 3. In the warm humid locations as defined in Section N1101.2.1:
    - - - 3.1. For asphalt roofing shingles: A 1-perm (5.7 × 10-11 kg/s m2 Pa) or less vapor retarder (determined using Procedure B of ASTM E 96) is placed to the exterior of the structural roof deck; that is, just above the roof structural sheathing.
    - - - 3.2. For wood shingles and shakes: a minimum continuous 1/4-inch (6 mm) vented air space separates the shingles/shakes and the roofing felt placed over the structural sheathing.
    - - 4. In Zones 3 through 8 as defined in Section N1101.2, sufficient insulation is installed to maintain the monthly average temperature of the condensing surface above 45°F (7°C). The condensing surface is defined as either the structural roof deck or the interior surface of an air-impermeable insulation applied in direct contact with the underside/interior of the structural roof deck. “Air-impermeable” is quantitatively defined by ASTM E 283. For calculation purposes, an interior temperature of 68°F (20°C) is assumed. The exterior temperature is assumed to be the monthly average outside temperature.

    Fiberglass insulation IS allowed by code, it does not require an ESR - it is spelled out in the code.



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  6. #6
    George Chittenden's Avatar
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    Default Re: Rafter Insulation

    Jerry,

    In reading the code sections you highlighted I do see that the use of an air-permeable insulation is allow in zones 2B and 3B. I f that is the zone the question is regarding then I stand corrected. All other zones require insulation the is not air permeable and in looking at the pictures the unfaced fiberglass is definately air permeable. Adding a vapor barrier below the unfaced fiberglass will solve the problem unless they are in the two exception zones.


  7. #7
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    Default Re: Rafter Insulation

    George,

    In looking at the referenced climate zone map, Austin is in the Zone 2 and is also below the Warm-Humid line.

    Thus, if that house is in Austin where Ken is, you would be correct - fiber glass insulation 'would not' be allowed by code.

    Going west of Austin a ways (about 40-50 miles would be my best guess), then that half of Texas would be in Zone 2B and 3B, except for the north-western corner which is in Zone 4B.

    Jerry Peck, Construction / Litigation Consultant
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  8. #8
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    Default Re: Rafter Insulation

    Jerry, Is fiberglass allowed in So cal? I was under the assumption it is not.


  9. #9
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    Default Re: Rafter Insulation

    Quote Originally Posted by Marc M View Post
    Jerry, Is fiberglass allowed in So cal? I was under the assumption it is not.
    Marc,

    Only if you are talking about the very small area at the tip of Southern California (see darker area in attached Climate Zone map from the 2006 IRC).

    If you go to Table N1101.2 Climate Zones by States and Counties, you will find which counties are in which zones.

    In California, the only county shown in Zone 2 - which is Zone 2 Dry (B) - is Imperial County.

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  10. #10
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    Default Re: Rafter Insulation

    Thank you.


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