nealtw

This article talks about it.
http://www.inspectapedia.com/Energy/Roof_Venting_Need.htm

GBR

If you don't want to vent the rafters, (as Andy Gump said), you need rigid or SPF (R-20) tight against the sheathing, then cavity insulation to meet your location's total R-value (R-38), see the chart map; http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting
The rigid foamboard requires canned foam at all edges for an air-tight seal. ADA the drywall to prevent air infiltration through any fiberglass/Roxul cavity insulation; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Gary

nealtw

GBR: If you look at the whole room. Massive amount of windows will be hard to heat the room. As cool as the windows make the room feel the area above the windows will be the warmest and adding more heat for comfort will make the ceiling warmer than normal. So with that in mind insulating with out a gap will require more insulation than can fit in the space. Evan if Drewdin puts foam board below the rafter as mentioned he will still have less over the wall above the windows which will have no insulation at all.
I beleive that "could" cause ice damming which would be bad enough for roof leaks and redo situation but with no headers over the windows the weight of an ice dam could also cause structural damage.
A little heat lose thru the ceiling may be good insurance when you think about one bad ice dam bringing down a structure.

drewdin

@GBR, would you recommend putting the rigid foam against the sheathing and then the roxul insulation? I planned on doing it the opposite way, roxul against the sheathing and then foam board. I have not mentioned it prior but the roof is a rubber in case that factors into anything. There is a 1" foam board and then its one giant sheet of rubber.

I don't plan on venting the rafters, it will take to much time and money that I don't have right now. I do plan on the Roxul R23 and a rigid foam board as I stated earlier. I will tape the foam board seams but its going to be hard to seal around the recessed lights.

I looked into spray foam and it would cost ~1500 to coat the area with 1", the foam board and roxul will cost $500. Its a no brainer...

I might get the DOW spray foam and seal under the recessed light and then add the roxul/rigid foam but thats only an R4.

drewdin

I also just realized that the electrician installed non-IC rated recessed lights in this area. Is this something i should have replaced? It would kill me to have 3" around each light that could not be insulated.

nealtw

I would want IC but I don't think you have room for them. Recessed lights are not a good idea here.

drewdin

Thanks neal, i hope i can make them work somehow.

nealtw

If nothing else you could flatten half of the ceiling, you would have room for the lights closer to the house wall.

drewdin

Hi neal, i got the electrician to replace the light fixtures with IC rated ones, on a side note. What do you mean when you say flatten half the roof? Thanks

nealtw

2x4s level from the house wall to about half way on the ceiling.