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.

  • 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. 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.