Best Way To Insulate Floor Joists. Fill the ends of joist bays with rectangles cut from rigid board insulation. We chose 2-in-thick R-10 extruded polystyrene Dont use expanded polystyrene which is a less effective air and moisture barrier.
The insulation should be pushed tight to the underside of the floorboards. At least 25mm of. See the Ecohome Building Guide pages for details.
Cellulose or wood fiber insulation is made from used newsprint other paper feedstock or wood.
One advantage of using spray foam to insulate rim joistsan approach sometimes called the critical-seal methodis that a single product performs two tasks. To provide additional insulation tongue-and-groove wood-fibre board can be fixed to the undersides of the joists. If you want to insulate a floor assembly by leaving the joist bays empty and installing rigid foam on the underside of the joists here are a few things to keep in mind. This is supported with plastic garden netting tacked into place.
