Radiant barrier foil stapled up on rafters before adding more insulation over existing batt insulation. Covering Exposed Batt Insulation that Cause “Hot Walls.” These are typically bedrooms or game rooms that share a wall with the attic space. Kneewall or Sidewall Application (foil directly over insulation in walls). Note the gap near the top ridge for proper ventilation. This gap is important regardless of the ventilation system your attic has. Don’t worry about the hard-to-reach lower corners, just get the big easy open areas. Remember to leave ventilation gaps at the top of each rafter run. If you have a hip or valley area, cut out an opening to allow the air in that area to vent properly. Easy installation with only a staple gun and a utility knife. Heavy foil will stay up with just a few staples and doesn’t rip or tear. A finished attic space can easily get to within 10 degrees of ambient temperature when you also have good ventilation in the attic.