Pole Barn insulation under new metal roof

[Beebazaar]

I have a 25 x 35 pole barn I will be rehabbing. currently I have shingles, but the previous owner had no ventilation and the shingles are kinda shot. I will be putting a metal roof in its place. I want to remove the shingles. and lay the roof over the plywood. I will need to repair some of the wood. what is the best recourse of action for condensation and insulation. I will insulate the entire thing in the future and may go as far as HVAC, but that is TBD as of right now. I would rather prepare through for the start.

I have read:
ply
roof felt
slip sheet
metal roof

no furring strips?
this will only help with condensation and keeping the roof dry correct? no insulation? so do i insulate from the inside? Inside are common trusses 2' OC. would i just use rolls between them? put up foam board or ?? if I have a ridge vent for the metal roof how does ot breath if I insulate the entire ceiling? pictures i see online and things I read the entire inside is buttoned up. I was always under the impression you need to have air flow. what am i missing.

 

[jack stand]

I might consider (after you've stripped the shingles) tar paper or synthetic underlayment. Then across the slope (not up) screwing down 2x4 @ 24" with 24" net space in between for a layer of 1.5" foam before you install the metal.
This will give you a much better fastening point for the metal than plywood, a 6-7 "r" value and the piece of mind with the underlayment.
Then your additional insulation inside is a little easier to achieve whatever "r" values you want. I'm not sure about the condensation concerns and someone might suggest the underlayment better the foam/metal. Personally I'd put any moisture protection against the plywood.

 

[Beebazaar]

under the foam? would you still put the sheathings between the foam and the roof?

 

[jack stand]

I would
Replace any water damaged (existing) plywood after the shingles and removed.

Roll out a modern roofing "underlayment" and fasten.

Run the 2x4's as described and for good measure use PT for both the first and last course.
(Eave and ridge)

Fill in with rigid foam, secure as necessary

Metal roof.

You may have to wait until you have the ridge cap in hand to locate the last purlin at the ridge. It needs to be where the metal ridge cap fastening "flange" is.

 

[RPH]

Use building wrap or tar paper between the pt treated lumber and metal or it will eat your steel, quickly.

 

[unimog1300]

Ujjjh