Hi. I hope I'm posting this in the right section. I recently had an Epdm roof installed on my 140 year old house. It's low slope and meets with a gable roof on the other part of the house. The Gable is standing seam. We had a tapered ISO board system installed as the underlayment to help with drainage and make the edge details easier to deal with. I reframed the roof and sheathed it myself before the roofing contractors started so I could save money. At the time the ceilings underneath the roof were all closed so I installed 4 inch rockwool batts right on top of the plaster/lath of the ceilings below. I was trying to maintain a 2 inch air space for ventilation and even though 4 inches doesn't give me much R value it was better than nothing which is what it had been before.
I then created a continuous soffit vent with cor-a-vent and made sure there was at least 2 inches of space between the old skip sheathing of the gable so that it could all share the same vent space. The roofers installed a ridge vent on the metal gable roof.
Long story short. I have since torn open the ceilings of 2 of the rooms under the EPDM roof meaning all the insulation I did above those rooms needs to be redone. I started researching again recently because of the cold winter we're having and realized that because I have ISO board on top of the roof sheathing, the roof assembly should probably be an unvented "warm roof" situation.
If so that's fine for the two rooms I have open. The other room will just have to stay the way it is.
My question is.....is my thinking correct on this? Should I ignore the fact that I built a soffit vent and just fill the cavity between the drywall and the underside of the roof sheathing? And if so is rock wool a good product to use considering I can really pack it in there much better than fiberglass. Note- the space is very small....too small to access from gable attic in any way. 6 inches at the eaves maybe 11 or 12 where it meets the gable
Also, if I really need to go with some sort of foam insulation could I get away with cutting sheets of 2 inch rigid foam, pressing it to the underside of the roof sheathing, spraying the voids and gaps with canned spray foam and then filling the remaining cavity with Roxul? I really don't want to rent a spray foam kit or hire a contractor for these relatively small spaces. Budget will not allow. Thanks.