Radiant barrier combined with spray foam thoughts
This is my first post so I hope I've found the right forum for my question.
I am enclosing my 11x31 attached patio and have been researching insulation options. What do you think of the following and please feel free to make improvements or suggestions.
The roof is sloped and shingled and supported by 4x4 posts on 8' centers all around.
I am in Kentucky so the climate is both hot and cold.
The outside wall is South facing with a 20" eave.
The wall plan is pretty standard - Vinyl siding on Tyvek on OSB on 2x4 studs and then Drywall.
My question is how best to insulate. I would like to try radiant barrier and closed cell foam of some sort instead of fiberglass.
This is what I'ld like to consider:
On the inside of the OSB in the 2x4 cavity, glue 4 - 3/4" foam blocks at the four corners. On these, install 1/2" rigid foam insulation (foil on one side) with radiant barrier facing the outside (OSB). This gives the required air gap for the RB. Then seal the perimeter with can insulation. Install another piece of Rigid but facing in toward the conditioned room, leaving another gap between the foil and the drywall.
So from outside to inside would be -
Vinyl siding - Tyvek - OSB - air gap - foil - rigid insulation - foil - air gap - Dry wall (whew!).
My thoughts are:
Vapor barrier - Tyvek, and Rigid will both provide a vapor barrier but will the gaps (osb-rigid & rigid-drywall) allow moisture that permeates the 2x4's to condense in the gaps?
Would the outside air gap get too hot as there is no ventilation there?
2x4 thermal bridge - would it be better to wrap the interior with foil to cover the studs and use thicker rigid (instead of two pieces)?
Ideas, comments, concerns anyone?
Last edited by rbobbitt; 01-08-2009 at 08:58 AM.