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Can I install ridgid polyiso insulation over old yellow pine attic floor boards?

Joshua Miller | Posted in Energy Efficiency and Durability on

I have an old farmhouse in WV, on the 2nd floor the floor joist’s are exposed and decked from the attic with 5/4″ yellow pine. Would I be able to install ridgid (closed cell) polyiso insulation directly over the floor boards and then cover with 1/2″ sheathing material or am I creating the potential for a moisture problem, if so would furring strips help to achieve air flow. If the ridgid is acceptable am I right in assuming that unfaced is better than a foil faced product. Space is limited in the attic so the ridgid insulation would help to cut down on my headroom issue.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Joshua,
    Is you attic going to be a conditioned attic? If so, you are planning to put the insulation in the wrong place. You need to insulate your roof, not the floor of the attic.

    If it's an unconditioned attic, why worry about headroom?

    Polyiso will not cause moisture problems in this application, but it is squishier than other foam options, so many builders would choose high-density EPS rather than polyiso. Remember, 1 inch of polyiso only has an R-value of R-6.5 or so. That's not enough insulation for a ceiling.

  2. Joshua Miller | | #2

    Martin,
    Thank you for your advise, I do have an unconditioned attic and will look into the EPS option, I will also consider a greater R-value given our location in Zone 6. Thank you again.
    Joshua

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