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  1. #1
    daniel nantell's Avatar
    daniel nantell Guest

    Default re; attic vapor barrier

    I recently inspected a home built in 1988 , and has blown in fiberglass insulation, I pulled some insulation back and checked for a vapor barrier and did not see any, I thought all attic spaces should have vapor barriers before blowing in the Insulation. thank for any Info.

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  2. #2
    A.D. Miller's Avatar
    A.D. Miller Guest

    Default Re: re; attic vapor barrier

    Quote Originally Posted by daniel nantell View Post
    I recently inspected a home built in 1988 , and has blown in fiberglass insulation, I pulled some insulation back and checked for a vapor barrier and did not see any, I thought all attic spaces should have vapor barriers before blowing in the Insulation. thank for any Info.
    N1102.5 Moisture control.
    The building design shall not create
    conditions of accelerated deterioration from moisture condensation.
    Above-grade frame walls, floors and ceilings not
    ventilated to allow moisture to escape shall be provided with an
    approved vapor retarder. The vapor retarder shall be installed
    on the warm-in-winter side of the thermal insulation.

    Exceptions:
    1. In construction where moisture or its freezing will not
    damage the materials.
    2. Frame walls, floors and ceilings in jurisdictions in
    Zones 1, 2, 3, 4A, and 4B. (Crawl space floor vapor
    retarders are not exempted.)
    3. Where other approved means to avoid condensation
    are provided.
    In cold climates, warm, moist air inside the building can
    migrate through the building envelope and condense
    on building surfaces or within building component cavities
    as the migrating air is cooled. In warm climates,

    moist outside air can migrate into a cooled building and
    can also condense on building surfaces. Vapor retarders
    can help protect insulation and building materials
    from moisture damage, degradation and decay by preventing
    the water vapor from entering the external
    building envelope component cavities. Inmoderate and
    cold climates, the vapor retarder is installed on the
    warm-in-winter side of the wall (the interior) to prevent
    migration of water vapor from the inside to the exterior.
    Although not always required by the code, vapor retarders
    in warm, moist climates are sometimes installed on
    the warm-in-summer side (the exterior) to prevent inward
    migration from the exterior.
    The warm-in-winter side is the interior side of the
    thermal insulation in the Climate Zones where this applies.
    Sheet polyethylene is often used as a vapor retarder.
    The perm rating for sheet polyethylene is significantly
    below the 1 perm (5.7
     10-11 kg/Pa  s m2) required by
    the code.
    The code requires installation of vapor retarders in all
    unventilated framed ceilings, walls and floors. Unventilated
    areas are framed cavities without vents or other
    openings that allow significant amounts of air to move
    freely through the cavity and insulation. For example, a
    ceiling vapor retarder is not required in a ventilated attic
    where the insulation is exposed to the ventilated space.
    Per the definition in Chapter 2, the vapor retarder must
    have a perm rating of 1.0 or less when tested with the
    desiccant method using Procedure A of ASTM E 96.
    The code also allows other approved alternatives to
    meet the vapor retarder requirements. A variety of materials
    act as a vapor retarder, even if not installed specifically
    for that purpose. For example, any material with
    an unperforated foil facing, some kinds of foam, some
    paints specifically formulated as vapor retarders and
    most kraft-faced fiberglass batt insulation would meet
    the 1 perm (5.7
     10-11 kg/Pa  s m2) requirement in the
    code. For unfaced materials, the permeability varies
    with material thickness. Most product manufacturers list
    a materials perm based on a thickness of 1 inch (25
    mm). Increasing the thickness of the material will decrease
    the perm. For example, 1 inch (25 mm) of
    extruded polystyrene, sheet foam product used for insulation,
    is about 1.1 perm, not low enough to be a vapor
    retarder by itself; however, increasing the thickness
    to 2 inches (51 mm) decreases the perm to about 0.55
    perm, meeting the code requirement for a vapor retarder.
    Note that it is possible to get the required perm
    rating based on several materials in series. For example,
    most floors are constructed so that the floor
    achieves the required perm rating without the addition
    of materials specifically designated as a vapor retarder.
    The code official or other authority having jurisdiction
    must approve this alternative based on reason of accepted
    principles or tests by nationally recognized organizations.
    The use of the exceptions needs to be evaluated on a
    case by case basis. Although the use of exception 3 will
    require review and approval of the proposed system by
    the code official, exception 2 will be a decision left to the
    designer. Although exception 2 does permit the elimination
    of the vapor retarder, the designer could still elect to
    include one or could elect to locate it at other than the
    warm-in-winter side. Such decisions must be made
    based on the historical experience in that location and
    consider the specific materials of construction. Exception
    1 allows exempting exterior envelopes constructed
    from materials that are not damaged by moisture or
    freezing from the vapor retarder requirement in any
    Climate Zone. This exception should probably be reviewed
    and determined applicable by both the designer
    and the building official before deciding that it is applicable.
    Even when using the exceptions, the key principle
    which is stated in the first sentence of the section

    should always be considered.



  3. #3
    Join Date
    Jan 2010
    Location
    sellersburg, in. work in lou, ky.
    Posts
    137

    Default Re: re; attic vapor barrier

    In our area as long as it is R-25 or greater there is no need for vapor barrier if I remember correctly, (sometimes I don't). I simply look for it, if it's not there look for evidence of any issue with it (usually there is not, if there is going to be it will likely be around penetrations through the drywall, light fixtures etc. where heat escapes) and document what I found and saw and tell them to monitor or if they are overly concerned people recommended infrared by qualified tech.. hope this helps.. Kenny


  4. #4
    Join Date
    Feb 2009
    Location
    Southern Vancouver Island
    Posts
    4,549

    Default Re: re; attic vapor barrier

    If it's an old house, paint is supposed to help a lot.

    Energy Savers: Vapor Barriers or Vapor Diffusion Retarders

    "Vapor barrier" paints are also an effective option for colder climates. If the perm rating of the paint is not indicated on the label, find the paint formula. The paint formula usually indicates the percent of pigment. To be a good vapor diffusion retarder, it should consist of a relatively high percent of solids and thickness in application. Glossy paints are generally more effective vapor diffusion retarders than flat paints, and acrylic paints are generally better than latex paints. When in doubt, apply more coats of paint. It's best to use paint labeled as a vapor diffusion retarder and follow the directions for applying it."

    Where I live, if it's a newer house, no mercy, it's got to have a poly vapour barrier with taped seams. We live and breath mould spores up here.


  5. #5
    Join Date
    Mar 2007
    Location
    Chicago, IL
    Posts
    2,797

    Default Re: re; attic vapor barrier

    Quote Originally Posted by kenny martin View Post
    In our area as long as it is R-25 or greater there is no need for vapor barrier if I remember correctly...
    Does anyone have a cite for this code or standard?

    Thanks.

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  6. #6
    Join Date
    Feb 2010
    Location
    Omaha
    Posts
    143

    Default Re: re; attic vapor barrier

    In most parts of the US poly is not needed. Only extreme climates will need it.

    In an attic as long as there is sufficient insulation the building material will not be below the condensing point- the ceiling and rafter will be on the warm side of the insulation. The attic should be able to vent any moisture. If not there is inadequate venting.

    Vapor diffusion through the material is very small and is not a problem. Most moisture is the result of air leaks. Generally there are so many penetrations in poly that is does do much.


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