Q: What are the different ways (and costs) of insulating cavity wall spaces?

A: The Brick Institute of America (BIA) established the following criteria for selecting suitable masonry cavity wall insulation.*
  • The insulation must allow the cavity to drain water.
  • The thermal resistance of the insulation should not be affected by moisture.
  • Granular fill insulating materials must be capable of supporting their own weight without settlement, to assure that no portion of the wall is without insulation.
  • Insulating materials must be inorganic: resistant to rot, fire, and vermin.
  • Granular materials must be pourable in lifts of at least 4 feet for practical installation.

The table shows the types, thermal resistance values (R), and cost of common insulation materials. The costs are from Colorado insulation suppliers. Check with your local suppliers for the exact thermal resistance and cost of their products.

INSULATION MATERIALS FOR CAVITY WALLS
Material Thermal
Resistance, R
(per inch)
Cost
Granular Fills:1
Vermiculite 2.27 $4.25/bag
Perlite 2.70 $5.00/bag
Rigid Boards:2
Expanded
Polystyrene
5.00 $0.55/sf
Foil-faced
Polyisocyanurate
7.20 $0.75/sf
1 A bag contains 4 cubic feet.
2 Price based on 2-inch-thick board.

* BIA Technical Note 21A, "Brick Masonry Cavity Walls Insulated," Brick Institute of America, 11490 Commerce Park Dr., Reston, VA 22091.