Insulating the attic of a house is important for heating and cooling inside the house. However, the ideal temperature of the attic/roof area is as near to the outside temperature as possible to prevent unnecessary condensation. Therefore, insulation should first be applied between the ceiling joists; this will allow insulation of the living areas of the home, without creating too much heat in the well-ventilated attic area. Additionally, insulation should never block inside or outside vents.
If the roof decking is the ceiling (as is the case with tongue and groove decking, with no attic space), insulation can be added in the form of rigid insulation on top of the decking rather soft insulation in the attic.