Whether using loose fill or batts put the vapor barrier closest to the warm side of your installation where hot moist air would get in facing the house s interior in cold climates beneath floor insulation and the attic s interior in hot climates on top of floor insulation.
Hot attic insulation.
Focus a lot of energy pun intended on the underside of the roof to keep the heat out of the attic and not just the floor of the attic.
The most important factor to consider in a warmer climate is the addition of a radiant barrier to whichever type of insulation you select.
Building codes vary among the thousands of jurisdictions but a typical requirement in hot climates is r 38.
A good way to gage if more insulation is necessary is to look in your attic for ceiling rafters.
In cold climates the best radiant barriers are installed on the floor of the attic so that they can redirect radiant heat from the home back into your living spaces.
Some regions don t require a vapor barrier.
And yet for example our fresno calif franchise abc cooling routinely insulates attics from r 50 to r 60 in home retrofits.
Common practice in some areas still has it pegged at r 19.
For hot climates where most of the radiant heat hitting the attic comes from sunlight radiant barriers should be draped from the attic ceiling or installed between the roof beams.
If you can see the ceiling rafters you need more insulation.
The two basic types of attic insulation are rolled insulation and blown in attic insulation.
With insulation more is usually better.