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  1. #1
    Join Date
    May 2020
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    Melville, WA
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    Default Roof Insulation - man cave

    Hi all,
    As some might know I have been working on my mancave.

    The roof is a colourbond steel roof with exposed beams. It gets hot - bloody hot. So I want to put insulation and ceiling (panels)

    The distance between the ceiling and the roof is 180mm.

    Looking at the insulation batts I have available in Perth (and I do not want to spend a small fortune)

    I can get the R2.0 (earth wool) that are 90mm thick or
    R3.5 batts that ate 175mm think...

    I presume that these will expand further.

    The question is can the 3.5 be used since they weill be butted against the roof or it does not matter. I am not sure if there needs to be a space between the batts and the roof. If I use these they will be packed well and truely tight as the beam spacing is about 850-900 wide.
    when I install the insulation I will be holding it up with fishing line then the panelling goes on for the ceiling.

    (I'm using these. Just a moment... )


    Also what about in winter with moisture. I do have some gaps where air flow is possible.


    Any comments will be warmly welcomed.



    Thanks again

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  3. #2
    Join Date
    Feb 2018
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    Shepparton
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    Default

    Can't help with batts to use but be warned that it will condense so condensation is I believe the main issue I personally have not noticed a great difference with a air gap between roof and batts.

  4. #3
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    Ignore this if someone with real experience posts, but Iíve read that an air gap is required if silvered foil is used. Itís also good if you can get a membrane that allows moisture to pass through but not return, so that it finds its way out. Iíve heard arguments that if the batts touch the steel no air will be present therefore no condensation will form. But if moisture does form it may rot the batts. Iíve also read that your location has an influence (ie. humid vs dry environments).

    Then Iíve seen sheds that have been insulated using silver foil backed with a batt coating, with the batt side against the steel. Youíd think the installers would know what they are doing. Maybe. Maybe not.

    Possibly the best plan is steel sheets > air gap > foil > air gap > batts > ceiling.

  5. #4
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    Standard recommended building practice is for a foil backed insulation blanket ( pink batt) directly in contact with the roof sheeting

    Look up any if the insulation or roof manufacturers installation manuals to see it.

  6. #5
    Join Date
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    Quote Originally Posted by ErrolFlynn View Post
    Youíd think the installers would know what they are doing.
    A very brave assumption in my experience.

  7. #6
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    Yeah, I know. It doesn't help people work out what's right when you are surrounded by so much that's wrong. I've found insulation much more complex than simply whacking some foil or a batt somewhere. Lots of different theories. Hence, my opening sentence.

  8. #7
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    Quote Originally Posted by Beardy View Post
    Standard recommended building practice is for a foil backed insulation blanket ( pink batt) directly in contact with the roof sheeting

    Look up any if the insulation or roof manufacturers installation manuals to see it.
    Quote Originally Posted by ErrolFlynn View Post
    Ignore this if someone with real experience posts, but Iíve read that an air gap is required if silvered foil is used. Itís also good if you can get a membrane that allows moisture to pass through but not return, so that it finds its way out. Iíve heard arguments that if the batts touch the steel no air will be present therefore no condensation will form. But if moisture does form it may rot the batts. Iíve also read that your location has an influence (ie. humid vs dry environments).

    Then Iíve seen sheds that have been insulated using silver foil backed with a batt coating, with the batt side against the steel. Youíd think the installers would know what they are doing. Maybe. Maybe not.
    I agree with most of the above and I must also mention it is impossible to have an air gap when laying wool and siso (foil) before the roof sheets go down because battens can be 40mm and wool siso is 50mm.

    During winter I removed my almost flat garage roof (4.5m sheets x 10 m coverage )and laid wool and siso then replaced the sheets, and the garage is much cooler now even though one long wall is zincalume sheeting and gets the north east sun to about 2pm.

    I did my own inspecting/testing during the work and found as mentioned, where the wool siso was already installed, there was no condensation early morning, but where I had not insulated there was condensation, lots of it.

    As to fitting batts between the joists, like everything, bigger is always going to be better but, consideration must be given to heat transfer through walls as well.

  9. #8
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  10. #9
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    This is an image from the video and it looks good. The insulation has been squeezed a little. So, that's not too bad. But the cutaway in the video is at the high point in the roof iron. There'll be just as many spots where there is zero gap, where the insulation has been squashed into near nothing.

    But there's not much that can be done about that. At least, not too easily. I doubt too many builds would have a double row of purlins (whatever) just to keep the insulation happy.

    Bradford.JPG

  11. #10
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    Quote Originally Posted by ErrolFlynn View Post
    This is an image from the video and it looks good. The insulation has been squeezed a little. So, that's not too bad. But the cutaway in the video is at the high point in the roof iron. There'll be just as many spots where there is zero gap, where the insulation has been squashed into near nothing.

    But there's not much that can be done about that. At least, not too easily. I doubt too many builds would have a double row of purlins (whatever) just to keep the insulation happy.

    Bradford.JPG
    Extra row of battens sometimes used for safety/fall protection

  12. #11
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    Quote Originally Posted by ErrolFlynn View Post
    This is an image from the video and it looks good. The insulation has been squeezed a little. So, that's not too bad. But the cutaway in the video is at the high point in the roof iron. There'll be just as many spots where there is zero gap, where the insulation has been squashed into near nothing.

    But there's not much that can be done about that. At least, not too easily. I doubt too many builds would have a double row of purlins (whatever) just to keep the insulation happy.

    Bradford.JPG
    The insulation gets compressed flat at every battern when you put your fixing screws in. That image is to make it look pretty for advertising purposes, a bit like how a McDonaldís hamburger looks in the ads haha

  13. #12
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    May 2020
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    Quote Originally Posted by Beardy View Post
    The insulation gets compressed flat at every battern when you put your fixing screws in. That image is to make it look pretty for advertising purposes, a bit like how a McDonaldís hamburger looks in the ads haha

    Thanks for all the feedback.

    Like I said I do not have the room for a two layer insulation. Also, it is only a mancave (gasp, did I just say that). The purpose of placing a layer of batts and a ceiling is to control the room temp.

    I'd like to know how many homes have been reported lately that have had that much rot as indicated in the bradford promotion. That is the reason for the roof ducts etc they are supposed to remove that moisture or at least dry it.

    I think I might go with the 170mm thick (R3.0). There are enough gaps around the top of the shed for air circulation.

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