Heat rises and therefore the building regulations requirements for heat loss through roofs are more stringent than those for walls.
How to insulate on roof 2x6 frames.
So your choices are 3 1 2 thick batt insulation for an r value of about r 11 9 or rigid insulation board for a r 20 to r 30 depending on the type of board.
Soooo then install the same perimeter wood blocking right over the roll roofing to match insulation thickness 5 or so of polyiso.
If you choose to use the 2x6 roof joists you ll only be able to fill the joist space up about 4 5.
Building regulations for insulating a roof.
However i want to add a wood stove for next winter.
Screw it down and glue down a 45 mil epdm membrane.
The insulation would be flush with the roof wall 2 6 s.
How to insulate a roof.
The building is unheated now and the condensation is not too bad.
Also adding 2 vents between each bay of rafters which are 2 oc that vent out my soffits.
I have a 14x26 cabin the roof is 2x6 10 pitch rafters with horizontal 2x4 purlins.
Nail 1 furring along every rafter side against the roof deck.
The limiting u value the maximise u value which cannot be exceeded required under current building regulations for the roof is 0 20w m.
Probably 1000 all put together for an r 49 roof in a 2x6 frame roof.
Then a vapor barrier over all that.
Tongue and groove pine over that then.
Cut and insert 1 or thicker high r foam insulation sheets r 8 per inch against the furring giving a 1 or greater air path between the insulation and the roof deck under the cathedral ceiling.