Adding insulation to a 1/12 pitch roof

I have a Mid-Century Modern home with a 1/12 pitch roof. The construction is 5 laminated beams running the length of the house with a cathedral roof/ceiling. The roof is 2x6 T&G running from the eaves to the center ridge. On top of this is 2" of hard foam glued to the T&G and covered in EPDM and EPDM is covered with river stones from marble to golf ball size (house was built in 1972). Of course the R-Factor of the roof is very low.
I am looking for an option on my thoughts to increase the R-Factor of the insulation.
I was thinking of removing the aggregate, placing 1" of hard poly foam glued and taped or spray foam in the seams over the EPDM, then running 1 set of strapping from the eaves to the ridge of plastic 2x2’s or 2x4’s screwed down through into the beams and T&G on 24" centers. Placing 1 1/2 hard poly between the straps and sealing the edges with spray foam. Then sheeting the roof with a synthetic/plastic 1/2" 4x8 sheeting. Covering this with waterproof membrane, then covering with a metal roof.
This should add 2" of foam total adding an additional R-14. I could add another layer of strapping and 1 1/2" of foam for another R 10 gain.
QUESTIONS:

  • Does the sound feasible?
  • I have found Plastic 2x’s online, but the sheeting is expensive Expanded PVC sheets, do you think I could use LP Smartside sheeting instead?
  • My whole issue is keeping the original foam and EPDM (tear off would be very hard) but am worried about burying wood between a layer of EPDM and waterproof membrane with no airflow in the insulated chamber, that is why I was looking at plastic 2x’s synthetic plywood type sheeting?
  • Can the metal roof be attached directly to the sheeting or do furring strips need to be added to raise it off the sheeting?
    Any advice would be appreciated.

https://www.kemper-system.com/US/eng/applications/plazas-irma/ Easier way to go. I know nothing of “Kemper roof systems”, it was the first IRMA example. Use 2 layers of offset insulation to stop the thermal break.

You are wasting your time.
No heat is penetrating into your home what so ever.