Foam roof deck or seal ceiling?
I am looking to improve the insulation and reduce air infiltration in an attic which has no lower ventilation because there is no overhang on the roof on all four sides. The ceiling area of the attic is about 865 sq. ft and it is constructed of 2 x 6, 24 inches on center. Currently, there is blown insulation which has settled or been disturbed throughout. At some point, a previous owner opened up three 16” x 16” open registers, simply pass thru-vents from the second floor ceiling to the attic, apparently to provide lower ventilation to the attic. They provide unnecessary air infiltration to the attic and we would like to close them off. There are mushroom vents on the top of the roof, (4) and a power vent which does not work. The roof deck is also 2 x 6, approximately 1180 square feet. We would like to improve the insulation levels in the attic as well reduce the air infiltration so blocking the registers makes sense, but that would leave us with no lower ventilation. So my question is, which would be a better alternative, sealing and insulating the second floor ceiling joists (providing lower ventilation with a vented drip edge system) or spray foam the roof deck and conditioning the attic?
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