Houses lose and gain energy through the movement of heat through solid objects such as walls, floors, and ceilings. Heat always moves toward colder air attempting to equalize the temperature. Insulation is helpful because it traps tiny pockets of air which retard the transfer of heat — it won’t stop heat entirely, but will slow it down.
Insulation effectiveness is tested by its R- value, its ability to resist the heat flow from warmer to cooler areas. The higher the R- value, the more effective the insulation. A material’s insulating ability is based on R- value, not thickness.
Types of Insulation
Batts & blankets
- Composition: Fiberglass
- R-value Range: 3.1 – 3.5 per inch
- Best suited: Standard joists, studs, rafter spacing in attics, walls, undersides of floors
- Composition: Cellulose, fiberglass, vermiculite
- R-value Range: 2.2 – 3.7 per inch
- Best suited: Non- standard spacing, in-fill of block walls, obstructed spacing between joists
- Composition: Polystyrene, polyisocyanurate urethane, bead board
- R-value Range: 3.5- 5.5 per inch
- Best suited: Basement walls, foundations, exterior walls, interior walls, cathedral ceilings.
Where to Add Insulation
Ceilings – Below an unheated attic.
Floors – Above unheated basements, crawlspaces, garages, and open porches.
Frame Walls – Uninsulated exterior frame walls.
Rafters – Between sloping rafters — leaving an air space for ventilation between the insulation and the roof.
Joists – In the back of band or header joists around the perimeter of the basement.
Basement Walls – When below- grade space is finished for living purposes or when the basement doesn’t enclose a gas or oil furnace or boiler, or when the above- grade exposure exceeds 50% of the interior wall surface.
Attics – Keep at least 1- 1/4″ space between the insulation and the sheathing so air from the soffit/eave vents can flow to the ridge and/or gable vents.