Poll: What is the best type of blow-in insulation to use in my attic?

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  1. #1
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    Apr 2009
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    Question Adding attic insulation questions

    I have a 1974 house with an attic that is about 5' tall in the center. It is currently insulated with about 6" unfaced fiberglass batts laid between the joists. This is rather skimpy, especially considering that I live in Fairbanks, AK where it gets down to -40 most winters. I am therefore looking at adding additional blow-in insulation (around R-33 was recommended) to the space. However, I have a couple of questions.

    First, I know I need to keep the eve and gable vents unblocked. I am a little confused as to how to do this though. I have heard things like using cardboard over the vents, or perhaps putting some 1x furring strips up along the edge to keep the insulation back, but I don't know what would be best. The situation is somewhat complicated by the size of the attic - all the do-it-yourself sites I have found show wide open attics with steep roof slopes where you can easily get to the edges. In mine, however, this is not the case. It is, as I mentioned, only about 5' in the center, and rapidly narrows down as you get towards the edges, making it a VERY tight fit to get out to the eves. To make things harder, it isn't the wide-open attic that I have seen in the guides, but rather a truss type system, full of criss-crossed beams, making access even harder. Given this situation, what would be the easiest way of keeping the vents clear?

    Secondly, I have been getting a lot of conflicting information about what the best type of insulation to use it. Some people are saying that blown-in fiberglass is better because it is non-flammable (I do have a wood stove chimney going through the space, so this is a consideration), and you don't have to worry as much about it getting wet. I have read a lot of people saying that you should never use cellulose. On the other hand, other people say that cellulose insulates better, and is cheaper, while being treated with fire-retardant chemicals that effectively nullify that advantage of fiberglass. So what's the truth of it? Which is the better option? Thanks.

  2. #2
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    Apr 2009
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    Default Re: Adding attic insulation questions

    It doesn't appear that I am getting much feedback from here. So is there somewhere I can go to get a good comparison between the insulation types? Or some good methods for keeping the vents open? Or perhaps somewhere else I should be asking? Thanks.

    Israel

  3. #3
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    Apr 2009
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    Default Re: Adding attic insulation questions

    No one? Really? So where should I go to get advice on things like this then, if not here?

  4. #4
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    Aug 2008
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    54

    Default Re: Adding attic insulation questions

    Quote Originally Posted by ibrewster View Post
    I have a 1974 house with an attic that is about 5' tall in the center. It is currently insulated with about 6" unfaced fiberglass batts laid between the joists. This is rather skimpy, especially considering that I live in Fairbanks, AK where it gets down to -40 most winters. I am therefore looking at adding additional blow-in insulation (around R-33 was recommended) to the space. However, I have a couple of questions.

    First, I know I need to keep the eve and gable vents unblocked. I am a little confused as to how to do this though. I have heard things like using cardboard over the vents, or perhaps putting some 1x furring strips up along the edge to keep the insulation back, but I don't know what would be best. The situation is somewhat complicated by the size of the attic - all the do-it-yourself sites I have found show wide open attics with steep roof slopes where you can easily get to the edges. In mine, however, this is not the case. It is, as I mentioned, only about 5' in the center, and rapidly narrows down as you get towards the edges, making it a VERY tight fit to get out to the eves. To make things harder, it isn't the wide-open attic that I have seen in the guides, but rather a truss type system, full of criss-crossed beams, making access even harder. Given this situation, what would be the easiest way of keeping the vents clear?

    Secondly, I have been getting a lot of conflicting information about what the best type of insulation to use it. Some people are saying that blown-in fiberglass is better because it is non-flammable (I do have a wood stove chimney going through the space, so this is a consideration), and you don't have to worry as much about it getting wet. I have read a lot of people saying that you should never use cellulose. On the other hand, other people say that cellulose insulates better, and is cheaper, while being treated with fire-retardant chemicals that effectively nullify that advantage of fiberglass. So what's the truth of it? Which is the better option? Thanks.
    One option would be to abandon the high/low venting in favor of all high venting. You would need to block off the gable and soffit vents and install roof vents nearer to the peak. This would allow you to completely fill the low areas and fluff the higher areas. For your area, I would recommend a value of at least R-50. To calculate for all high venting, take the area of the attic in square feet, divide be 300 and multiply the result by 144, giving you the net free vent area required in square inches.
    Our agency uses cellulose for most situations, which does contain a boric acid fire retardant. I've actually tried to ignite some with a propane torch and it will not burn. Cellulose must be kept away from metal or masonry though, so shielding around any existing chimneys or vent pipes is necessary, as well as any recessed lights or exhaust vents not rated for insulation contact. Exhaust vent pipes, if you have any, should be wrapped with R-11 duct wrap or equivalent to prevent condensation in the pipes. Blown fiberglass is an option, but the cost is about 5 to 6 times that of cellulose. Rolled fiberglass is only effective if there are no gaps. I have seen very few homes insulated with rolled fiberglass that was done or could be done properly.

  5. #5
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    Apr 2009
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    Default Re: Adding attic insulation questions

    My concern with Cellulose is that I've been told the fire retardant leaches out over time - so while it may be completely non-flammable when I first put it in (as you say, even taking a blow torch to it doesn't make it burn), years down the road that may no longer be the case. If this is true, then fiberglass would be worth the higher cost- saving several hundred dollars is not worth it if the house burns down later Of course, if it is put in properly, perhaps that isn't an issue anyway, or at least a minimal risk. Thanks for the response!

  6. #6
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    Default Re: Adding attic insulation questions

    Quote Originally Posted by ibrewster View Post
    My concern with Cellulose is that I've been told the fire retardant leaches out over time - so while it may be completely non-flammable when I first put it in (as you say, even taking a blow torch to it doesn't make it burn), years down the road that may no longer be the case. If this is true, then fiberglass would be worth the higher cost- saving several hundred dollars is not worth it if the house burns down later Of course, if it is put in properly, perhaps that isn't an issue anyway, or at least a minimal risk. !
    Hmmmm ..... me thinks you had better do some more research ..... you're getting some misinformation.

    Besides considering your home is likely built using wood which is also likely not treated with a fire retardant .... also flammable materials like furniture and other items ......it's somewhat a moot point for the insulation being non-flammable.
    Last edited by canuk; 06-12-2009 at 10:01 PM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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