I own a two story colonial in New Hampshire. I have started to removed the plaster and lathe from the interior to retrofit insulation. The exterior of the house is clapboards with aluminum clapboards over it. The exterior has no house wrap or tyvek type material. The interior walls or 2x4 rough cut. My question is about poly vapor barriers and sealing. Since the house has no house wrap it is drafty. I would like to stop this draft but not sure of the proper way to do it. I figured a polyvapor barrier attached to the studs as the last item before drywall would stop air infiltration. I have heard conflicting information though about the vapor and the way the building breathes. Should I or should I not use the poly vapor barrier? My other question is about how to insulate. Again with wanting to get a tight wall I had though about putting 1/2 polyboard in the stud bays against the exterior sheathing and sealing the edges with expanding foam. After that I would put a unfaced fiberglass batt of 3 1/2 inches over and finish with the poly vapor barrier. But again the whole building breathing is what has me wondering. Also someone before me has put poly sheathing d****d over the ceiling studs from the top in the attic and then placed fiberglass batts over that. Is this correct? Should I actually tear down the ceiling, attach a vapor barrier and then sheetrock it? I know this was long winded but I appreciate any help! Thanks.