You need a vapor barrier just above the sheetrock, below the insulating fill. Either the kraft paper that comes on the faced bats, or sheet plastic. Most would use the Kraft-faced batts or else use plastic sheeting if using blown-in celulose insulation.

It depends on where you live, the HVAC system and the construction of the walls and attic space.

thanks for repsonding guys I very much appreciate any information you can give.

I live in NY on Long Island. The house is a 1 story ranch with a high peaked attic center of attic is about 7 feet. The walls on first floor is tounge and grove covered by Aluminum siding (I plan to vinyl next year if that matters) The house is heated by Baseboard heaters conected to a a furnace. There is a full basement. In the attic there is 3 windows. I hope this can help. If more info is need please let me know.

The vapor barrier goes between the living space and the insulation. It's purpose is to keep warm moist air from migrating into the cool insulation and condensing. If you have the drywall off the ceiling, kraft faced fiberglass is probably the easiest thing to do. Use the thickness appropriate for your ceiling joists. Once you've done that you can add more in the attic by using unfaced fiberglass bats going perpendicular to the joists, blown in celluose, or blown in fiberglass to reach the appropratie R value. Remember you're probably looking at R-38+ and your local building department can tell you what the minimum R value is for your area.

You only need to allow for airflow at the soffits if the soffit is actually ventilated. Not all are. They sell little "channels" made of Styrofoam or cardboard that you staple in place to keep the insulation from interfering with the airflow.

I'm just across the sound from you in CT.

6-mil poly is a more effective vapor retarder than kraft faced bats. If FG is your insulation of choice, I'd recommend unfaced batts between the joists and 6-mil poly as your vapor retarder.

The poly would be stapled up on the bottom of the joists, so it'll be sandwiched between the ceiling drywall and the joists.

Don't combine kraft and poly. Use one or the other.

As Mike wrote, your soffits only need to be open if you have soffit vents.

Assuming the attic is not used for anything, if it is open and ventilated and there is adequate exhaust from the bathrooms you don't need a vapor retarder at the ceiling for you location. You would need one if you lived in a much colder climate like northern ME and it would need to be sheet polyethylene.

If you feel you must have one, foil-backed drywall would be the easiest to install. Then insulation could be more easily installed from above the attic joists (if the joists are open).

To all those that responded, thank you for very much for taking the time to. I much appreciate the information that you all gave.