I am looking for advice on some insulation. I have a front entryway to my house which had a plaster & lath ceiling. The plaster and lath was sadly beyond repair and it had to come down. Before I put up a new plaster ceiling I noticed a lot of ice cold air coming in from the outside (I have a front porch that goes out about 8 or 10ft.
At first I was going to have spray foam installed a few inches thick right in the rafters of the porch where the porch meets the house, creating a wall of insulation and keeping the cold air out. My problem is there is nothing to spray foam against....My porch rafters (12" high) are just connected to the house and go all the way to the end of the porch.
I basically need to create some kind of "wall" in each of these 6 rafters that creates a insulated barrier and I am not sure what to use. Someone had suggested cutting rigid foam boards to fit the openings and then using caulk and then one component spray foam to seal. Similar to putting foam board inside a stud bay, except I currently have no outside sheathing!
I only have access from the inside, not thru the porch ceiling (original wood I am not willing to take apart)
1) Should I use some kind of board first such as OSB or some kind of sheathing first? If so, recommendations?
2) If I can just cut rigid foam and put it in place, what kind of foam? I was thinking 2" thick, but the kind I currently have is foil faced on both sides? Do I want foil or not, one side or both? I don't know much about vapor barriers and don't want to get this wrong.
3) Finally, what is best to hold the rigid foam in place? Caulk followed by great stuff? Tape? Having the insulator come back and spray foam such a tiny area is not really cost effective, so I will rely on the foam insulation & possibly roxul as a second layer before re-plastering the ceiling.
Any advice to steer me in the right direction would be greatly appreciated. It is getting cold outside so I need to figure out a good solution and get it done