I need some help…..
I have a cantalevered section of our breakfast area where the underside needs to be weather proofed. The old section of 1/2 plywood that was acting as the soffit rotted out. There was a deck that was installed that prevented access to the area. I am in the process of rebuilding the deck and I need to replce the soffit section with something that will hold up to moisture and humidity.
My initial plan was to use 1/2″ MDO that is primed and paited with exterior paint. I was also going to cut in soffit vents and insulate the joist bays with R19 fiberglass insulation. One problem I run into is the new deck will effectively close off a lot of circulation underneath the deck in that area. This was due to new footing guidelines with my county (a very long story I posted a few weeks ago). The picture shows the cross section of the new joist system I am using.
My concern is with humidity rotting away a section of 1/2 MDO over time. One thought I had was to use 3/4″ exterior plywood primed and painted. Or, using a vapor/water membrane over the MDO or plywood. Air circulation may become an issue since the joists and beams are only about 4″ off the ground.
Any thoughts on how to prevent the soffit from rotting out again?
Edited 7/6/2008 9:21 am ET by Mike126