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I am in the process of doing some design for a roof system on a 30x48 unconditioned shop building built on a concrete slab with a moisture barrier and a gable style roof. The trusses are steel and set 12' o.c. and connected with horizontal runs of 2x6's set on edge 24" apart from the eave to the ridge. The manufacturer recommends attaching the metal roofing panels directly to these 2x6's. I live in north central Florida and would like to add insulation to the roof as well for the summer heat. I see in most of your responses you talk about having air space and ventilation under the steel roofing in a vertical fashion to promote natural convection I assume but that doesn't seem to be an easy thing for me to achieve. I work in a commercial steel building that has a plastic faced insulation in direct contact with the roof and the eave ends are sealed with a foam closure so that there is no air space and we do not have any problems with condensation. I am thinking of attaching some type of rigid foam insulation with a vapor barrier maybe 2" thick to the underside of the 2x6's and closing the eave edges and ridge with foam closure to seal up the air space left. I figure if there is no moisture in the 5.5" of dead space and it is sealed so nothing can get in, then there should not be a problem with condensation. I would appreciate your advice on this.
2/24/2004
2/26/2004