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Insulating sloped ceiling

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  • Insulating sloped ceiling

    See attached diagram of the cross-section of my house's second story.

    The ceiling slope is about 5 feet long. The space between roof and sloped wall is currently stuffed with batt insulation, thus blocking airflow from lower attic (where soffit vent installation is underway) to the upper. That space is just a few inches deep. Seems to me that foam insulation sheathing is my only option for insulating the sloped walls. Does that sound right?

  • #2
    other than foam insulation, batts or faced insulation has to remain fluffy to do any good. the vapor barrier always faces the living space. sprayed insulation may be another option as it is the most air tight

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    • #3
      The rafters should be 2x8 or 2x10 lumber, this gives enough room to install up to R30 insulation with baffles. Baffles are usually made of Styrofoam and are shaped to have channels in them they are installed against the roof decking and then the insulation is installed. These baffles hold clear airways in the insulation and should be installed the entire distance where insulation would be in contact with the underside of roof decking.
      Little about a lot and a lot about a little.
      Every day is a learning day.

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      • #4
        The rafters are 2x6 - see image. House was built in the early 1960s when people tended to stuff insulation inside sloping walls. I've managed to pull out some of the insulation from inside the sloped ceiling. I'll need some long conduit or PVC to push out the rest.

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        • #5
          With 2x6 rafters you actually have 5.5" of rafter (maybe a real 6" if the house is old enough) the baffles will cause a min. of 2" compression in parts. R19 requires 6.5" of space.
          Soooooooo R19 without baffles would fit or very close and maintain a full R19 insulation value, however you must have the baffles, you could install the baffles and the R19 which would probably be an effective R17 of insulation value, it will be tight getting the insulation in.
          or you could install R15 with baffles and achieve a realistic R15 insulation level and a much easier install.
          Spray foam insulation would be easier (as someone else is doing it ) with baffles or without baffles but much more expensive.

          hope this helps !
          Little about a lot and a lot about a little.
          Every day is a learning day.

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          • #6
            Lowe's sells some R-15, but it's quite expensive and it's designed with soundproofing in mind. The squirrels aren't on the roof often enough to make soundproofing worth it. Home Depot sells R-13 (same 3.5" thickness) so I'll plan on going with that.

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