How to Figure Cubic Feet for Insulation

Originally the only insulation in most homes was provided by the wall materials themselves. Modern buildings are usually constructed with cavity walls: two parallel brick walls a few inches apart. The air trapped between the walls reduces heat loss; however, the efficiency can be greatly improved by replacing the air with blown cellulose that reduces convection and airflow. The density of the cellulose determines the efficiency, and Canada's Office of Energy Efficiency recommends a minimum of 3-1/2 pounds of insulation per cubic foot of wall cavity.

Pipe and cable detector
Metal tape measure
Electric hammer drill
1-inch masonry drill bit
Flashlight

Instructions

- 1
  Select an unobtrusive section of wall to drill an inspection hole. Scan the surface of the wall with a pipe and cable detector. The operating procedures vary between makes and models, but the general approach is to switch on the detector, calibrate it then scan the target area. If pipes or cables are present, the detector will bleep, or a warning light will flash.
- 2
  Fit a large masonry bit into the chuck of an electric hammer drill. Check that the bit is properly centered then tighten it with the chuck key. Remove the chuck key before connecting the drill to a power source. Drill a hole through the wall then the outer layer and stop when the bit enters the cavity.
- 3
  Slide a metal tape measure into the hole until the end touches the brickwork on the opposite side of the cavity. Use a flashlight to peer into the hole and measure the distance across the gap. Record that distance.
- 4
  Multiply the width of the gap in inches by 0.0833 to convert it into a decimal fraction of a foot. For example, if the gap is 5 inches wide, the equivalent is 0.417 feet because 5 multiplied by 0.0833 equals 0.417.
- 5
  Measure the height and length of every wall to be filled with insulation. Multiply the height by the width to determine the surface area. For example, if a wall is 20 feet long and 15 feet high, the surface area is 300 square feet: 20 times 15 equals 300.
- 6
  Multiply the surface area of each wall by the width of the internal cavity expressed as a fraction of 1 foot. The result is the volume of the cavity. For example, a 300-square-foot wall with a cavity 0.417 feet in width has a cavity volume of 125.1 cubic feet -- 300 multiplied by 0.417 equals 125.1.
- 7
  Multiply the volume of the cavity by the number of pounds of insulation required per cubic foot. The result is the cubic feet of insulation required to fill the wall. For example, a 125.1-cubic-foot wall filled to a density of 3 pounds per cubic foot requires 375.3 cubic feet of insulation because 125.1 multiplied by 0.417 equals 375.3 cubic feet.

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