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  1. #1
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    Mar 2009
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    Unhappy New, conflicting advice on insulating vaulted ceiling

    I want to insulate and finish the ceiling in our attic space, which we will use as a home office. Everything I've ever read over the years indicates that in between the insulation and the roof sheathing, I should leave an inch or so layer of space for air to convect from the soffit vents to the ridge ventilation, to prevent moisture buildup.

    I'm applying for a local program that is subsidizing energy retrofits. It's being conducted by an organization that has a long and impeccable track record in a variety of programs. They built this program using state-of-the-art energy conservation training and professionals.

    One thing they are telling me that I'm having a hard time wrapping my head around is that as part of the overall remediation, I won't need this ventilation, and we can insulate right up to the roof sheathing.

    Has anyone here seen projects in which this was the case? Before talking to them, I would have said "No way!" to anyone who suggested it. But they tell me that they are aware that the venting I expected has always been necessary, but won't be required for my project due to the whole-house approach they are taking to sealing and venting.

    So I'm hoping for responses from people who have knowledge of the approach the program is recommending, not just others like myself who have never heard of such a thing and are also likely to just say it is wrong. As I would (and did)!

    Thanks!

  2. #2
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    How can you teach an old dog new tricks?

    Unless they can back their theory with money saving facts, insulate with a gap.

    The trouble is that they completely neglect the moisture factor, and that's why the gap is necessary (to allow draft to keep the area dry).

  3. #3
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    There are a lot of factors here. What type of insulation are you using? Do you have a ridge vent or are you planning on installing one? Will any part of your ceiling be flat or is the cathedral part going all the way to the peak? Will there be knee walls?

    If for example, you will have a small flat (horizontal) ceiling down the center of the room and knee walls on the side and you are using fiberglass insulation, then you absolutely need the gap.

    If instead you are sheet rocking all the way to the peak, using foam insulation and you have no ridge vent, then the gap would not be needed.

  4. #4
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    your best bet is to contact the local building authority as to what is required in your region. they can give you the most up to date codes and methods that are being accepted currently.

    codes and methods will vary from region to region be it building practices or the climate
    fire up the saw and make some dust

  5. #5
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    May 2011
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    Use spray foam, seal it completely and you'll have better insulation value, no moisture, and quieter too.
    1925 Two-Story Stucco Beaux Arts Neoclassical

  6. #6
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    Quote Originally Posted by keith3267 View Post
    There are a lot of factors here. What type of insulation are you using? Do you have a ridge vent or are you planning on installing one? Will any part of your ceiling be flat or is the cathedral part going all the way to the peak? Will there be knee walls?

    If for example, you will have a small flat (horizontal) ceiling down the center of the room and knee walls on the side and you are using fiberglass insulation, then you absolutely need the gap.

    If instead you are sheet rocking all the way to the peak, using foam insulation and you have no ridge vent, then the gap would not be needed.
    Thanks all who replied... I'll see what they are planning to insulate with.

    It happens that we currently have exactly the flat ceiling/kneewall configuration you describe, and for which I had the air gap ventilation recommendation. In the remodel though, we plan to sheetrock to the peak (with exposed collar ties), and insulate down to the soffits to bring the storage areas into the insulated envelope. So the kneewalls will remain but be an interior feature not impacting the insulated envelope. We have no ridge vent, though there are a series of individual vents every few bays to vent the current shared micro-attic above the ceiling that will be going away. I just realized as I type this that I will need to seal those off =:-0

    I knew that foam wouldn't need the gap, but I'm pretty sure they aren't spec'ing that. I'll get the skinny from the actual program contractor and post the details.

    BTW, in answer to a few other responses: The program was put together with the full participation of the city's building permit department, etc. (We actually have a "fast track" permitting process for green building projects as a builder incentive.) And the incentives are tied to completing the improvements using program-approved contractors who have met a standard of up to date green building techniques, so whatever they are proposing has had a lot of visibility and vetting.
    Last edited by ramatsu; 08-15-2011 at 01:56 AM. Reason: typo; misplaced quote, additional thoughts

  7. #7
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    Since you are rocking all the way tot he peak and you don't have a ridge vent, then there won't be a need for the gap above the insulation. The gap is for ventilation and you won't have any ventilation at the peak, so were would the hot air go?

    I would hope they are using a closed cell foam for this application.

  8. #8
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    Default Re: New, conflicting advice on insulating vaulted ceiling

    Quote Originally Posted by ramatsu View Post
    Thanks all who replied... I'll see what they are planning to insulate with.

    It happens that we currently have exactly the flat ceiling/kneewall configuration you describe, and for which I had the air gap ventilation recommendation. In the remodel though, we plan to sheetrock to the peak (with exposed collar ties), and insulate down to the soffits to bring the storage areas into the insulated envelope. So the kneewalls will remain but be an interior feature not impacting the insulated envelope. We have no ridge vent, though there are a series of individual vents every few bays to vent the current shared micro-attic above the ceiling that will be going away. I just realized as I type this that I will need to seal those off =:-0

    I knew that foam wouldn't need the gap, but I'm pretty sure they aren't spec'ing that. I'll get the skinny from the actual program contractor and post the details.

    BTW, in answer to a few other responses: The program was put together with the full participation of the city's building permit department, etc. (We actually have a "fast track" permitting process for green building projects as a builder incentive.) And the incentives are tied to completing the improvements using program-approved contractors who have met a standard of up to date green building techniques, so whatever they are proposing has had a lot of visibility and vetting.
    Closed cell spray foam in this case would be the ideal material . Otherwise it will be very difficult with say batt insulation to ensure an air tight seal around all the exposed rafter ties.
    I would be asking them to provide an IR camera scan of the finished job before handing over payment.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  9. #9
    Join Date
    Mar 2009
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    Smile Re: New, conflicting advice on insulating vaulted ceiling

    Quote Originally Posted by canuk View Post
    I would be asking them to provide an IR camera scan of the finished job before handing over payment.
    That's a great idea. They certainly took a lot when doing the assessment, but it only makes sense to confirm the quality of the work the same way. Thanks!

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