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  • ThePracticalPeasant
    replied
    Originally posted by Grandpa View Post
    Now my question: the ceiling joists are 2X6 and I want to insulate the ceiling but don't want to use fiberglass instead I want to use Styrofoam. Do I need an airspace between the roof and foam? Any suggestions are appreciated.
    Styrofoam will be a huge job - it should be cut to fit to precisely fit the joist cavities and glued in with PL300.
    The white (crumbly) stuff is not a vapour barrier, the "rigid" style foam is, but note the effort required to cut to size and glue it into place.
    I'd be concerned that if you got water again, though the insulation wouldn't absorb the water, you have a higher probability of mold/rot as it may take longer for the water to seep through into the living space to give you an indication that there was a problem. Further, rigid Styrospan (or whatever brand) competes with the cost of sprayed polyurethane (plus your labour to install it).

    Fix the roof problem and ensure that the roof is maintained and the worry about water in the attic space becomes moot.

    Originally posted by Inspector Ron View Post
    The spray foam should be applied directly on the underside of the deck plywood. Typically, a closed cell ( 2lb) foam would be used and then a vapour barrier would not be required.
    If the attic is vented, yes. If the attic is NOT vented, I'd spray the underside of the roof deck, making the attic space a warm zone and install vents in the ceiling to allow air circulation into the attic space.
    Note that though closed cell foams will achieve a vapour seal, a minimum thickness of 2" is required (and will result in approximately R14; R7/inch).

    All this said:
    If this was my house, I'd install vapour barrier on the warm side of the ceiling joists and have standard blow-in insulation installed.
    If you're absolutely set on not using glass-fibre/cellulose/etc, I'd have it sprayed with 2lb foam, either the ceiling joists or the rafters, as noted above, depending on the size of the space and the existing venting.

    ​​​​​Edit: It sounds like there is no plywood on the attic side of the ceiling joists - in this case, the ceiling would need sheeting first and the foam sprayed from the inside the attic. Though this method creates a great seal, there's a substantial risk of pushing the panelling off the ceiling as the foam expands. An easy solution is to get a roll of cardboard and sheet the floor of the attic with it (overlapped and stapled) to provide a backer for the foam that can now be sprayed "up" from the living space. Feel free to ask for further details if any of this isn't clear. (I'm certified to spray 2lb polyurethane in Canada, solving this type of problem is my day job).
    Last edited by ThePracticalPeasant; 07-20-2021, 04:04 PM.

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  • Grandpa
    replied
    A lot has happened since my first posting. I wanted to use foam so if I ever had a leak it wouldn't become waterlogged. Pulling down the the waterlogged insulation I realized this was going to be far more then I could handle being disabled and coming off of 8 months of chemotherapy. Every single piece of insulation was waterlogged as the water ran across the top of the vapor barrier. So I contacted my insurance company and they sent out a cleanup person for an estimate. As inspector Ron suggested he recommended spray foam and I would pay for the difference from the fiberglass batts. I can live with that. An adjuster is coming out in the next few days. I got all the rust off my midi lathe and talon chuck and oiled it up. Bowls I have made were full of water but they will dry out so little harm done. A plastic box of small turning rounds was full of water and they turned black but I think when they are turned it will come off. If not I can pass them off as exotic wood.

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  • Inspector Ron
    replied
    The spray foam should be applied directly on the underside of the deck plywood. Typically, a closed cell ( 2lb) foam would be used and then a vapour barrier would not be required.

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  • ThePracticalPeasant
    replied
    Why do you want to use styrofoam instead of fibreglass?

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  • Bill R.
    replied
    I'd suggest 1" at least.

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  • Grandpa
    started a topic Deck insulation

    Deck insulation

    On the back of my house I have a covered deck attached to my house. The ceiling is insulated and covered with wood paneling. Unknown to me the flashing where the deck joins the house failed and during last week's heavy rain my eavestrough overflowed and water ran into the ceiling. I had water pouring out every ceiling joint. Today I have been taking down wood paneling and soggy fiberglass. Llucky for me I used my pneumatic pin nailer so it easily pulls down. No mould, it hasn't had a chance to start yet. My midi lathe in a small nook was totally flooded but now is cleaned and oiled.
    I will be removing my eavestrough temporarily and putting in wider flashing.
    Now my question: the ceiling joists are 2X6 and I want to insulate the ceiling but don't want to use fiberglass instead I want to use Styrofoam. Do I need an airspace between the roof and foam? Any suggestions are appreciated.
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