Hi,
We are in the process of converting our 22′ x 8′ screened porch into a heated space in Vermont. I’ve attached some photos. The floor and ceiling are 2×6, 24″ o.c. and I replaced the screens with five 6′ insulated low E vinyl sliding doors. This allows us to keep the screened porch feel during the summer by opening five doors w/screens.

Part of the house’s vented soffit (22′) is inside the porch area.. I want to completely box in under the soffit and go up vertically with an insulated knee wall to the porch ceiling. The porch is about 2′ off the ground and I will be skirting it in the future (slatted). Last year, I installed radiant heat under the floor between the joist which allowed the heat to rise nicely between the 1/2″ gaps on the 2×6 painted pine decking. I will be installing wide plank flooring over the existing deck and will urethane it. Last season I temporally put up 4″ DOW board I had laying around (floor & ceiling) so I could experience the porch during the winter. It heated nicely, but without properly insulating it, I got some expected condensation drips from the ceiling.

I want to use Roxul ComfortBatt then ComfortBoard to achieve a decent R-value on the floor and ceiling. I was planning on insulting as follows, but I have many questions.

CEILING::
> 5.5” R-23 Roxul ComfortBatt up to ship lap (no air space)
> R8 Roxul ComfortBoard
> poly Vapor retarder,
> 1” urethaned pine ceiling

FLOOR::
>1” urethaned hardwood
>1.5” existing pine decking
> radiant pex: radiant/vapor barrier,
>5.5” R-23 Roxul ComfortBatt,
>R8 Roxul ComfortBoard across joists
> Aluminum pest screen or plywood.

1) What do I do about the soffit vents inside the porch area?
2) Do I need a air space between the Roxul and ship lap roof board on the ceiling?
3) Do I need to vent the triangular space I’ll create from boxing in soffit? Sidewall vents?
4) The ceiling has been painted. Will this create a vapor trap once I install a vapor retarder?
5) The radiant floor heat is between the joists, should a radiant/vapor barrier be installed directly under touching the radiant pex with Roxul butted up to it?

6) Is plywood over the Roxul ComfortBoard a good idea?

Any guidance is appreciated. I want to do this right.

Thanks