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What is the method to create a conditioned attic and keep a vented roof?

John_70 | Posted in General Questions on

We live in the humid south (Memphis area – zone 3), and the home we purchased and moved to a few months ago was originally built in the late 1970s. In order to improve energy efficiency, keep pests out, and create a semi-conditioned storage space, we want to insulate the roof assembly and eliminate the fiberglass insulation on the attic floor. I lean towards the sealing benefits of closed cell spray foam, but I am very hesitant to spray it directly on the underside of the roof sheathing (40+ year old house and 8-10 year old roof).

Is it a crazy idea to screw radiant barrier OSB to the underside of the rafters (with the shiny side facing out towards the roof) and then use 1-2 inches of spray foam on the attic side for continuous sealing? What type of additional insulation might be best to go over the spray foam to supply the R-value, because this would now be a bumpy surface with no rafters exposed? – I could screw some form of rigid insulation through the closed cell foam and into the new layer of OSB. This method would leave the rafter bays wide open for airflow with soffit and ridge vents.

Another idea I am considering is installing continuous baffles in each rafter cavity, then spray foaming 1-2 inches, then a soft form of insulation to fill the remaining rafter cavity, then screwing rigid foam insulation to the rafters to eliminate thermal bridging and finish out the appropriate R-value.

I plan to do the majority of the work myself, although I would consider hiring the spray foam portion. I am inclined to think that the radiant barrier aspect could be beneficial, and it would be easier to judge the thickness/evenness of the spray foam on the flat surface than in individual rafter bays. Are both of these ideas crazy? Do you have any other suggestions?

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi John.

    I suggest you read this article which will give you a number of options for your roof: How to Build an Insulated Cathedral Ceiling.

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