Hello:

My floor has an 18" x 60" extension beyond the foundation on which the zero clearance fireplace sits.

I am about to close off the bottom, on the outside, and wondered if I need to install VB on the warm side of all the cavities between the joists etc before I stuff the cavities with Roxul insulation.

Any info on this would be appreciated.

Rob.

If you have continuous wood from top to bottom you will provide a place for warm air moisture to condensate so yes you would need v.b.
If you finish the outside with a layer of eps to provide a total thermal break and you detail the exterior as 100% air tight, then you would not need a v.b.

Thanks FBBP

Would 2" of eps under the floor (between the joists) plus 5.5" of Roxul between the joists and then cover the whole 18" x 60" opening with 2" eps (nailed to the bottom of the joists) and then cover with finishing be OK?

Would 2" of Polyfoam XPS do instead of eps?

Thanks,

Rob.