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  1. #1
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    Feb 2013
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    Default Old attic insulation

    I recently bought a 60 year old cottage that's originally a log cabin plus 2 additions over the years. The attic spaces do not connect and they are insulated but unvented. The asphalt shingle roof is 20 years old and still in decent shape--I have maybe 5 years before needing to replace. My question is about the insulation. There is R13 foil-faced fiberglass on the ceiling and stapled up in the rafters. Is this OK or would it perform better if I pulled down the rafter batts & laid them on top of the ceiling batts?

  2. #2
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    Sep 2009
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    florida
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    Default Re: Old attic insulation

    [QUOTE=guy48065;274959]The attic spaces do not connect and they are insulated but unvented. QUOTE]

    For the insulation to do any good you need to make sure the entire attic is vented. Other wise your wasting your time
    Gizmo

    Cut it 3 times & it's still to short.
    Inventor of the Miter Master Plus.

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  3. #3
    Join Date
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    Default Re: Old attic insulation

    It is code to have an attic properly vented. Are you sure you don't have vents up there?

  4. #4
    Join Date
    Feb 2013
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    The thumb, MI
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    Default Re: Old attic insulation

    [QUOTE=Gizmo;274970]
    Quote Originally Posted by guy48065 View Post
    The attic spaces do not connect and they are insulated but unvented. QUOTE]

    For the insulation to do any good you need to make sure the entire attic is vented. Other wise your wasting your time
    Hold my hand here...how is it better to insulate my conditioned space from an attic with cold air moving through it, than a warmer sealed attic?

  5. #5
    Join Date
    Feb 2013
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    The thumb, MI
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    Default Re: Old attic insulation

    Quote Originally Posted by dj1 View Post
    It is code to have an attic properly vented. Are you sure you don't have vents up there?
    I've flipped through some FHB mags at the bookstore & seen articles on sealed vs. vented attics so what code are you referring to, does it vary by municipality, and does it apply to a 60 year old log cabin?

  6. #6
    Join Date
    Dec 2010
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    Houston Texas
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    Default Re: Old attic insulation

    You want to achieve an insulation layer all around the conditioned space. By venting the attic you decrease the moisture levels inside the attic. This moisture comes from condensation cause by temperature differentials between inside the attic and outside the attic as well as the house below. A moist attic will rot out from the inside. Your roofing nails should be nice and shiny 20 years later, not all rusted and streaky.

    In the summer months, a vented attic keeps the roof cooler and makes the roof last much longer. You don't want to cook the shingles off the roof.

    Owens corning has some cool videos. Scroll down to the attic insulation tips.

  7. #7
    Join Date
    Feb 2013
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    The thumb, MI
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    54

    Default Re: Old attic insulation

    I haven't tried to crawl out to the eaves to verify. The soffits are covered with perforated soffit siding...but that's no guarantee, of course. Since my roof is so old, dry, no curling shingles, no leaks, fluffy insulation with no telltale compressed spots from old leaks...I have to assume I've got excellent ventilation.

    Now about my original question...
    Should I leave the batts up against the roof deck--leave it alone?

  8. #8
    Join Date
    Dec 2010
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    Houston Texas
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    2,363

    Default Re: Old attic insulation

    Shove in those insulation spacers between the insulation and the roof sheathing

  9. #9
    Join Date
    Dec 2007
    Location
    Tennessee
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    1,381

    Default Re: Old attic insulation

    The question is not as simple as you ask. What type of roof? Is it a hip roof or does it have gable ends? If it has gable ends, are the walls of the gable insulated?

    Do you plan on using the attic as living space? Are you going to heat and cool it?

    If you have gable ends and their walls are not insulated and you are not going to use the attic as living space, then absolutely you should tear down the rafter insulation and insulate the ceiling joists. There are a number of good reasons for doing this.

    1. Radiation surface. Lets say that the attic is 1280 sq ft. (32x40) If you insulate the ceiling joists, then you have 1000 sq ft of insulation to install and you have a radiating surface of 1280 sq ft. If you choose to do the roof instead and you have a 6/12 pitch, then you have 1431 sq ft of rafters space to insulate plus the gable ends. If the gable ends are 8' tall by 32' wide, that is an additional 256 sq ft to insulate. Thats a total of 1687 sq ft to insulate and it is 1687 sq ft of radiating surface.

    2. Limited thickness. You can only go as thick as the rafters allow if you do rafters but you can really blanket on the layers between and above the ceiling joists.

    3. Ventilation. As warm moist air rises through the insulation, it meets with colder surfaces and on these colder surfaces, the moisture in that air will condense. In fiberglass, the condensation will lower its insulating factor by half. Against the wood, it will cause rot. You need an air gap above the insulation to allow the cold dry outside air to come in and absorb some of the heat, that in turn raises the airs ability to hold moisture which it will draw from the warm moist air escaping from below. That will keep the insulation and the wood structures dry, increasing the insulating factor of the batts and protecting the wood.

    If you insulate the rafters, then you need a vent at the soffit and at the ridge of each rafter bay. This usually means a perforated soffit and a ridge vent at the top of the roof. and you need a gap between the insulation and the underside of the roof. If you insulate the ceiling joists, then you only need a vent in the gable wall at each end of the house.

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