Insulation for EPDM Roof question

[joseph moore]

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.

[Peter Quinn]

These are some pretty technical questions for a wood working forum. Might be better off posting on FHB site or JLC, not saying nobody here knows this stuff but its certainly not the focus, hate to see you get bad info and do damage to your roof system.

[joseph moore]

Thanks for that. I did post on FHB and TOH as well. Not JLC. Good idea. I had searched on here and found similar insulation queries mostly in regards to workshop spaces though. Just thought I'd give it a try.

[Shawn Pixley]

I have an EPDM roof (mechanically fastened & fully heat welded) on my house. This is similar to comercial construction. Mine is 2x12 ceiling joists and 2x12 rafters with no open access. Mine is unvented. I have 12" Batts of fiberglass throughout. I would recommend as much insulation as possible. I wouldn't do either of your suggestions. Insulation is the cheapest way to reduce your bills and increase your comfort.

You didn't state where you live, so this is a shot in the dark so to speak. Consider closing the vents and blowing in insulation over the entire ceiling. I don't know whether you have drain pans in the flat potion (I do). But if you did, and you live where it freezes (I don't), I would want to ensure that water doesn't freeze in the pan and block up the drainage.

I am unfamiliar with the ISO board. My sheathing is 3/4" T&G ext ply glued and screwed with 1-1/2" rigid nailable insulation over the top.

[joseph moore]

Shawn. Thanks for getting back to me. I live in the NE so yeah......freezing temps as we speak. I might not have described my intentions well enough but the two options I described would be different versions of packing it with as much insulation as possible. The thing is.....I've read that this is only a good idea if there are no air gaps. Sounds like a pain. If I installed sheetrock first, I could conceivably drill holes and blow in cellulose but I think it would settle and leave an air gap. ISO board is a type of rigid foam insulation so I think you and I have the same roof. That's the thing. The ISO board has R value of 5.8 per inch so a vented space under that would seem to mean condensation. I don't know. This building science stuff makes me crazy. Wish me luck. Thanks again.