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Room above garage

goodheat | Posted in GBA Pro Help on

One more question on my room above garage. The home is in zone 5 and the garage is 24’x24′ The floor system has 16″ deep tji 16′ on centers. I will be filing between the joists with mineral wool and then Solitex Mento for air tightness with 2 1/2 ” of 8lb Roxul IS Board as a thermal break then covered with 5/8″ drywall. I plan on using strapping 24′ oc however where should it be placed. Should I place 2×4 strapping 24″ oc with mineral wool board in between and then a layer of mineral wool board with 5/8 drywall or the revers with a layer of mineral wool board first and then 2×4 strapping and mineral wool board and 5/8 drywall. I’ve looked at the diagram for adding mineral wool to the exterior house wall and applied it to garage ceiling. I’m concerned with the extra weight and bulk and the best screws to use for the 2×4 strapping and drywall.

Any suggestions will be appreciated

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  1. GBA Editor
    Martin Holladay | | #1

    It would be better to put the strapping 16 inches on center rather than 24 inches on center, because that will make it easier to install your 5/8-inch drywall ceiling.

    The strapping should be installed last, on the bottom layer, so that the drywall can be screwed directly to the strapping, with no intervening mineral wool to complicate the drywallers' job.

    As you probably know, mineral wool panels are a little squishy, so your chosen method of insulating will be a little fussy. You may have to adjust the screws used to fasten your strapping a few times, until your strapping is level and co-planar.

  2. goodheat | | #2

    Martin, I'm going to forgo the mineral wool. I came across the article BSI-009: New Light In Crawlspaces by Joe Lstiburek and will be using 1 1/2 foil faced isocyanurate taped and air sealed as the thermal break. with additional Isocyanurate board between the strapping.

    Thanks for all your advice

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