Insulation?

[Ironman1079]

Well my buddy (a handyman) is finished framing walls, running all the electrical, done installing shower and all plumbing is done for new bath upstairs. I am having an insulation company come out this week to insulate the whole upstairs. They are putting 12 inches of insulation in the ceiling, and 3-1/2" in my knee walls, sloped ceiling and in exterior walls. They are going to use unfaced insulation in the exterior walls and then put the plastic poly sheet on top, all other walls will be kraft faced.
Is it better using the poly sheet or do they just do it that way because it is cheaper?

The whole living part of the upstairs is about 29' x 19', and they quoted me $548, sound like a good deal?

[Wgoodrich]

You have differing opinions about your question. My opinion the plastic sheeting is better than using paper back insulation as vapor barrier due to the whole sheet less gaps thoughts.

You mentioned 3 1/2" in sloped ceilings. This probably is not enough unless you are no matter where you are. It depend on geographic location but in middle USA you are required R 30 and 3 1/2" fiberglass is R 13. You really need to investigate the R rating required in your area for ceilings and install that. Many times a second framing is installed to get the 10 or so inches insulation required leaving the required 1" air gap between roof decking and you insulation for roof venting. Many times the frame a ceiling joist is done and sometimes scabbing onto the bottom of the rafters will get you the area needed for the required R factor for ceiling insulation.

Do your research or it will cost you in the long run in heat bills.

Wg