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help with attic insulation

Post in 'DIY and General non-hearth advice' started by Nutmeg Warrior, Oct 7, 2013.

  1. Nutmeg Warrior

    Nutmeg Warrior New Member

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    Hey all, I am struggling with what is probably a typical problem.

    My attic has a large area of plywood flooring underneath which is an inadequate layer of old, dirty and somewhat compressed fiberglass batts. I know in an ideal world I would tear up all the flooring and add several more inches of insulation. However, I don't really have the time to tackle such a project. Plus we are using some of this area as storage.

    I am wondering if adding a layer of polyiso on top of the plywood would be an effective way to add some r-value. I think polyiso could handle the weight of holiday decorations and such. Would adding rigid panels create any moisture problems since there is already a vapor barrier on the fiberglass?

    Also, could I just roll unfaced fiberglass batts over some of the plywood that I don't need for storage?
    Last edited: Oct 7, 2013

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  2. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    The polyiso won't take much walking on it, but it would support Xmas decoration boxes OK.

    It there is an air space between the top of the existing insulation and the plywood, that would limit the effectiveness of the added polyiso by letting air circulate between the two. Maybe blow some cellulose in there before adding the polyiso? You could get some of the other parts of the attic at the same time?

    Or, consider adding some 2 by 4 framing on top the existing plywood, fill in the spaces between with insulation, and add new plywood on top?

    Atlas RBoard polyiso has face sheets that are stiffer and would hold up better to a little walking than the the regular foil faced polyiso.

    Gary
  3. velvetfoot

    velvetfoot Minister of Fire

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    How about closing off the attic and spraying the underside of the roof? I heard it's done nowadays.

    (I realize it's not really a practical solution in this case-maybe I should delete the post?)
    Justin M likes this.
  4. woodgeek

    woodgeek Minister of Fire

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    I think your aiming at the wrong target. You need to airseal the floor of your attic. If you haven't done this yet, all the heat and moisture is going around your insulation. Google 'attic airsealing' for a lot of great DIY instructions. I reduced my heating bill >25% just by caulking gaps around the top plates in my attic floor, and covering large holes around plumbing and chimneys with foam board or sheet metal, maybe 20-30 hours of DIY work total. Improving the insulation has to be done afterwards, and has less benefit than the aisealing. In my case going from R-15 to R-50 will save me only 10% or so of my heating bill.
    BoilerMan and midwestcoast like this.
  5. Nutmeg Warrior

    Nutmeg Warrior New Member

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    Thanks for the ideas guys.

    I think I need to use a combination of these to get where I need to be. I did some air sealing along with constructing a box for covering the attic stairs, but I am sure there are plenty of other penetrations I need to deal with.

    I don't think I will use blown cellulose. I used that stuff at another house and it's just so incredibly messy. Also, if you ever need to do work in the attic you have to kick around this dusty shredded pile of newspaper.
  6. DBoon

    DBoon Minister of Fire

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    Same problem - floorboards over 6" of fiberglass in the attic. I put another 8" of fiberglass on top of that. Luckily, I don't have massive airsealing issues so it was pretty effective.
  7. midwestcoast

    midwestcoast Minister of Fire

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    I am absolutely pro insulation. In an attic I will tend to over-insulate because it's relatively cheap.
    In this case though I would say either find the time to get up there and do a FULL air-sealing first, or do nothing & wait 'till you have the time.
    Anything you do on top of the flooring would make airsealing more work later & you may never do it.
    Swedishchef, BoilerMan and woodgeek like this.
  8. TradEddie

    TradEddie Minister of Fire

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    One more vote for air sealing first. Look for areas of dirty fiberglass, that's expensive heated air from your house leaving through the attic.

    TE
    BoilerMan likes this.
  9. EatenByLimestone

    EatenByLimestone Minister of Fire

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    Another vote on air sealing. I finished off the attic before I really considered air sealing. I ended up opening walls to get at some of the air leaks that melted areas of snow on the roof. I'm in the process of foam boarding my crawl spaces. The last one remaining has a plastic vapor barrier. Before I seal it with the foam I want to see how well that plastic is doing the job. It's much more work going back and fixing something that is easy to do before you start.

    Matt
  10. semipro

    semipro Minister of Fire

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    You'll get better value for your time/money if you air seal first, then insulate.
    Otherwise you're just installing an expensive air filtration system.

    Having used both fiberglass and cellulose in attics, I'd rather deal with old newspaper any day rather than have fiberglass penetrating my skin, eyeballs, and lungs.
    I wear Tyvek coveralls, goggles, and positive pressure respiratory protection when in my fiberglass filled attic and still leave itching and hacking.
  11. laynes69

    laynes69 Minister of Fire

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    +1 on airsealing. We cut our heat load quite a bit with just airsealing. Took a while on and off when I had time, but every crack and void filled saved us money and increased comfort. That alone even before adding insulation, made a huge difference.
  12. EatenByLimestone

    EatenByLimestone Minister of Fire

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    There's quite a bit of time chasing the point of least resistance for air movement. You fix one spot and another seems to appear. Once you knock them out, you really notice a difference in the drafts and how warm the house feels. Windy days really help since you can feel the air blowing in and can fix the problems as you find them.
  13. mass_burner

    mass_burner Minister of Fire

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    Does CT have a state sponsored energy audit program? Here in MA they come out and do an energy audit blow door test and then you decide what you want done. I had my basement, attic and doors air sealed. Then my complete attic added with 9" blown in. They even made 2 insulated attic entrance doors. All this cost just $800. And I have 24 recessed lights!
  14. kingston73

    kingston73 Member

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    I was just about to say this exact thing. Between the air sealing and the extra insulation it's amazing how much easier it is to keep the house warm (or cool during summer).
  15. Dana B

    Dana B Feeling the Heat

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    Air sealing the attic is a must. I recently did this in my own attic. I found that none of the holes that had been drilled for plumbing and wiring were air sealed so I hit them all with some Great Stuff. When dealing with the fiberglass batts a sure sign of unwanted airflow going through them is discoloration. Over time the batts become grey and black as the air passing through them brings with it dirt and debris. If it's at all possible and cost effective to do so I'd remove the batts and replace with closed cell spray foam. Spray foam is expensive but also by far a better insulation product when compared to fiberglass batts.

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