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DIY spray foam and hot roofs

Post in 'DIY and General non-hearth advice' started by Cynnergy, Mar 18, 2014.

  1. Cynnergy

    Cynnergy Feeling the Heat

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    Lots of threads on here lately about insulation, so I thought I'd chime in with mine.

    I'm thinking of insulating the cabin (attic ceiling and beneath the first floor - there is no crawlspace or basement, just open space under the house - it sits on log skids). There is currently some sort of 1950s rockwool (gyproc brand I think) in at least some of the walls, but no other insulation anywhere.

    I think I'll do between the floor joists with Roxul (to prevent mice issues in fibreglass), but I am puzzled over the attic. There is living space up there, so I would like to insulate between the rafters in the attic ceiling. There are no soffits or ridge vents, and each end is hipped, so I think I need to insulate it as a 'hot roof'. In order to do this and deal with moisture issues, I think I need at least R20 of spray foam or rigid foam boards because we're in zone 5. We're on an island so getting a spray foam contractor out will be $$$, but cutting 4 or 5 inches worth of 2' wide rigid foam boards to fit between 24"OC rafters sounds like a nightmare. Has anyone ever tried a DIY spray foam kit like here: http://tigerfoam.ca/? Seems kind of dodgy to me.

    Any other ideas? I would be grateful for any help.

    Pic for an idea of the layout:

    cabin.JPG

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  2. semipro

    semipro Minister of Fire

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    I priced out the DIY spray foam kits and found them to be the most expensive way to go per unit volume. The price was even higher than the 16 oz cans.
    Foam board was the best value based on material costs only, no labor.
    Given that the labor sounds like a lot in your case I'd suggest that finding a good spray foam contractor is your best option.
  3. Cynnergy

    Cynnergy Feeling the Heat

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    Thanks semipro. I guess I should get a few quotes before making decisions.
  4. semipro

    semipro Minister of Fire

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    I'm sure others here will chime in eventually. I think everyone is out enjoying the first days of spring.
  5. kingquad

    kingquad Minister of Fire

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    If your shingles nearing the end of their lifespan, you could foam board on top of your roof deck.

    http://www.danperkinsroof.com/pdf/metal-roof-venting-and-insulation.pdf

    You could do something like this, but it's an expensive solution. It would last you the rest of your life though. This method is widely used/talked about over on greenbuildingadvisor.com too.
    BoilerMan likes this.
  6. BoilerMan

    BoilerMan Minister of Fire

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    My recommendation as well. If you want to go with asphalt then you just do a plywood sandwich over the 2-4" or foam. You can use 2x sleepers for proper ventelation as well. It also does not change any looks inside the cabin is that is important as well.

    I would not recommend using blue board for this application, polyiso is the way to go.

    TS
  7. Warm_in_NH

    Warm_in_NH Minister of Fire

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    Depending on how consistent your rafter spacing is you can rip the 2" rigid on a table saw or with a skill saw.
    Rip it a little light, put it in place and then just seal the edges with spray foam. It'll hold it in place and make it air tight.
    Ideally, space it down with a furring strip so it's not tight to the roof, then you can add a soffit and ridge vent and have the air flow that it needs.
  8. fbelec

    fbelec Minister of Fire

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    just was speaking with a close friend about what he used. he used the tiger spray. said it worked very well.
  9. G-rott

    G-rott Member

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    Q: Why do you need air flow in your roof system?
    A: To carry away moisture.
    Q: If you air seal with foam board will there be moisture to carry away?
    A: Not if it is done correctly and the roof surface is properly maintained
  10. Cynnergy

    Cynnergy Feeling the Heat

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    Hi all,

    Sorry didn't realize this had been moved to the DIY board. Thanks for all of the replies!

    Yes, I had considered foam board on top of the roof sheathing, but I was out-voted before we redid the roof (we put on cedar shakes that hubby hand-split himself - with a bit of help from our roofer friend).

    If I do insulate, will I be able to tell when/if the roof starts leaking? We plan to maintain the roof well, but shakes don't last forever. We did put on zinc strips, so hopefully that will stop the moss from getting to it too quickly.
  11. mike van

    mike van Member

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    You burn wood at that house and put a cedar shake roof on it?
  12. Cynnergy

    Cynnergy Feeling the Heat

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    Yep. It is the traditional material and believe it or not was the cheapest option for roofing. There were some decent cedar shake logs on the family property that the old-timers hadn't bothered with so hubby hand-split them all with a froe and mallet. Total price = sweat equity.

    I'm not too worried, but we won't light up the stove if it's really dry. Considering it's generally damp here for 8 months of the year, that shouldn't be a big issue.
  13. EatenByLimestone

    EatenByLimestone Minister of Fire

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    How did that Super 27 work for you this winter?
  14. Cynnergy

    Cynnergy Feeling the Heat

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    The Super 27 was great! We only use it on the weekends and our wood is/was sub-par so I'm looking forward to having better wood next year. I'm glad we went with a mid-size stove, even though the cabin is only about 900 sq ft it still takes a few hours to get everything heated up in the dead of winter. I was slightly worried about it being too big but it's not at all. I might even cave and put the electric blanket on the bed next year, but we'll see how much quicker we can get the stove up to temp with better wood. The stove size can be a bit much at this time of year, but small fires in the morning and the evening generally are working really well. We're still getting down into the mid-40s F (~7 C) here at night, so with almost no insulation it is still chilly in the cabin at night. We had our first afternoon over 70F today, so the time where we don't have to light the stove is coming ==c.

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