08-07-2008, 07:31 PM
What exactly do you mean by "plastic"?
Plastic is not an insulation product as far as I know. Assuming the basement is unheated and vented, there are two things needed: 1) a airblock to stop cold air from circulating up through any breaks in the floor (i.e. along pipes and the like); 2) an insulation product that provides R-value.
The usual way to do this is to detail all the breaks through the floor with expanding foam and the like, then use either rigid insulation or kraft-faced batts (or perforated plastic encapsulated batts) to jam up against the floorboards. The plastic/kraft can act as an airblock for old leaky floorboards but is insufficient for pipe pass-throughs.
If you use rigid styrofoam insulation panels you can cut them to fit and jam them up between the joists against the floorboards. Alternatively you can put in a continuous layer attached directly under the joists, though this will be a bit less effective because of the large air gaps (joist spaces) above them (note that that the joist spaces absolutely must be hermetically sealed all around or the insulation will be utterly useless. The styrofoam panels will give you much more insulation per inch than fiberglas, are easy to install, and are not so susceptible to gaps which can occur around fiberglass batts and render them virtually useless.
Did I understand correctly that you are insulating the basement walls? That makes no sense if the thermal envelope is the basement ceiling. You need to concentrate on the ceiling. Forget the walls unless you are going to live down there.
Plastic is not an insulation product as far as I know. Assuming the basement is unheated and vented, there are two things needed: 1) a airblock to stop cold air from circulating up through any breaks in the floor (i.e. along pipes and the like); 2) an insulation product that provides R-value.
The usual way to do this is to detail all the breaks through the floor with expanding foam and the like, then use either rigid insulation or kraft-faced batts (or perforated plastic encapsulated batts) to jam up against the floorboards. The plastic/kraft can act as an airblock for old leaky floorboards but is insufficient for pipe pass-throughs.
If you use rigid styrofoam insulation panels you can cut them to fit and jam them up between the joists against the floorboards. Alternatively you can put in a continuous layer attached directly under the joists, though this will be a bit less effective because of the large air gaps (joist spaces) above them (note that that the joist spaces absolutely must be hermetically sealed all around or the insulation will be utterly useless. The styrofoam panels will give you much more insulation per inch than fiberglas, are easy to install, and are not so susceptible to gaps which can occur around fiberglass batts and render them virtually useless.
Did I understand correctly that you are insulating the basement walls? That makes no sense if the thermal envelope is the basement ceiling. You need to concentrate on the ceiling. Forget the walls unless you are going to live down there.