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Insulating an Attic space for storage

Tareyton | Posted in Energy Efficiency and Durability on

House is in Charleston SC area.

I have an attic space off of one of my upstairs bedrooms.  It is rather large and there is a door from the bedroom into it.  I want to insulate it so I can use it for climate controlled storage.  By climate controlled I just mean I don’t want it to get to 120+ in the summer.

the backside of the interior walls have R13 fiberglass insulation.  Exterior walls and roof have none.  Above the bedroom is the regular attic so there are vents at top of walls into this space so attic can breath through the eves.

I am considering the following and looking for input.

Continuous foam board on all walls with R13 fiberglass.  Fill exterior walls with R13 fiberglass and then a continuous foam board.

for roof either extend vents and use a R19 fiberglass covered by continuous foam board layer or install furring strips to create a 1 inch gap which will act as a vent channel and fill in between rafters with three layers of 2 inch foam board and seal gaps with spray foam.  Rafters are 7 inches deep.  I believe code for roof is R38. I don’t know how to get that with only 7 inches plus don’t know if I really need to since space will just be for storage.

thoughts?  Want to do it right but also not spend extra money if I don’t have to.

see pictures.

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  1. user-2310254 | | #1

    I am concerned that you won't be able to establish an unobstructed ventilation space between the eaves and the roof peak. It might be better to use a two-part kit to foam the underside of the roof sheathing. You could use a combination of closed-cell and fiberglass or just go with all open-cell. I would probably use foam on the divider walls as well to air seal this newly conditioned space. Last, ideally I would try to add a HVAC supply to the space to mitigate humidity and closet "smells."

    That's my amateur perspective, and the professionals likely have other ideas. As you are waiting for more responses, you may want to read Martin's article on insulating cathedral ceilings:

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