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Does one need to ventilate a small roof area when replacing old fiberglas insulation with closed cell polystyrene?

EJ Palma | Posted in GBA Pro Help on

Thank you very much for your quick response. The bathroom tub area extends 4’6″ from the back wall of the house and is 8′ wide. As I stated before there is a ventilated soffit with 2″ strip vents around the total eaves area of the house. The 8’shed roof does tie in to a ventilated attic space. If I am understanding correctly, it would be unwise to eliminate that part of the continuous eaves venting because the 8″ width ties to an existing ventilated attic. I do not mean to be redundant and ask again, but am I understanding you correctly. This is a confusing situation only because now it seems that recomendations are that closed cell insulation does not need to be vented. My initial feeling because it is a rehab of an existing was that I should keep the air space to the vented attic and the continuous eaves venting. Again I appreciate your help in clarifying the confusion. Thanks Ed

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Replies

  1. Riversong | | #1

    You started a new thread instead of responding in your existing thread.

    But the answer is yes, if the shed roof vents into the main roof, you'll be better off maintaining that intake vent, which means installing some 1" spacers on each side of every rafter (can be 1" rips of XPS foam board) to maintain a vent channel. Then you can build down with additional XPS and finish with a thermal break of foam board below the rafters.

    The foil-faced foam won't offer any radiant advantage unless there is an air space on one side of it. But having a vented roof will help lower ceiling temperatures (as well as reducing the likelihood of ice dams) and reduce summer radiant gain.

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