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Seeking Garage shop/breezeway insulation input

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  • Seeking Garage shop/breezeway insulation input

    Hey everyone,
    I知 considering insulation options and I知 wondering if I can insulate my wall from the inside in this fashion using silvrboard.

    Exterior to interior: siding, house wrap, osb sheathing, exterior studded wall with rock wool batts, 6mil vapour barrier, 1 1/2 silvrboard, 1/2 drywall.

    I知 not touching the siding which is why I致e got the silvrboard on the interior side of the studs. If this is do-able do I have the 6mil vapour barrier in the correct spot? My plan is to bridge the thermal gap of the studs with the silvrboard and either screw the drywall directly through foam to studs or possibly add furring strips over the foam.

    My plan also is to insulate between rafters by using foam rafter vents from the top plate of the wall up to the ridge and then batts in the rafter bays. This would be so I could continue to use rafter ties and trim storage areas.

    This is is my plan so far but I知 100% open to any suggestions as I知 in the initial stages of this project.
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  • #2

    Re: Seeking Garage shop/breezeway insulation input

    It depends on what silvrboard is and whether or not it has it's own vapour barrier because you do not want 2 VB's.

    When you mention Rcck Wool are you talking about Roxul or something else? Rock Wool is an older product.

    What is the Rvalue in the walls and what will the Rvalue be in the rafters?
    "Do it Right!"

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    • #3

      Re: Seeking Garage shop/breezeway insulation input

      Sorry, silverboard is a eps rigid foam with a reflective polypropylene coating. It says it does act as a vapour barrier when taped so maybe using an unfaced foam with the 6mil poly would be a better and cheaper option.

      Rockwool is is the new rebranding for roxul in North America. It痴 the spun mineral material. I like it痴 fire resistance, ability to wick moisture and in my limited experience irritates me less than fibreglass batts and is a little easier to work with.

      The walls would be around r21 with 1 1/2 eps foam and r14 batts. The rafters would be only r14 but I could build them out to accommodate a 2x6 batt which would be like r20-24 depending on the batt rating

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      • #4

        Re: Seeking Garage shop/breezeway insulation input

        If it is what I was thinking about it's pricey stuff. Green on one side and silver on the other. I paid $16.00 for a 4x8 sheet of it on a particular job. If you already have 6 mil up I suppose you could put this against your 6 mil but any moisture between the 2 would stay there, so plain foam board might be better. On your rafters building them down to get as close to R30 as possible as a minimum would be better and a high collar tie on the rafters to create an attic space with a ridge vent or high roof vents would be good as well to gain real good airflow which not only sucks air in from the soffit but emits the air through the high vents. That way you could still retain the use of the storage space.
        "Do it Right!"

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        • #5

          Re: Seeking Garage shop/breezeway insulation input

          Yeah it痴 pricey, I was able to find the 1 1/2 at 20$ a sheet but it seems like unfaced eps is the way to go.

          In this unfaced eps case would the vapour barrier go on the warm interior side of the foam or still stapled to the studs with the foam planted over. I.e siding, housewrap, sheathing, insulated stud bay, 6mil poly, foam, drywall.

          Thats a great idea with the high collar ties! Thanks a lot for the help!

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          • #6

            Re: Seeking Garage shop/breezeway insulation input

            It would probably depend on the type of foam as in open celled or closed cell. In most cases i prefer vapour barrier on the warm side because it can't hurt anything but there are differing views when it comes to types of foam in that the foam can eliminate the need for poly VB's.
            "Do it Right!"

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