The Thermal Insulating Value of Concrete

Insulating Value Measure

• The unit of measurement that is used to signal a material’s effectiveness as an insulator is the R-value. It is calculated by dividing the thickness of the material by its thermal conductivity. This second part of the equation is a complex calculation involving joules of energy passing through a squared area of material over a certain amount of time. The important thing to note is that the higher the resultant R-value, the better a material is at preventing heat flowing through it.

Unadorned Concrete

• Used on its own, without any additional insulation, concrete does have an R-value, but it is not very high at all. A 4-inch-wide block has an average value of 0.8; an 8-inch block averages 1.11 and a concrete block with a width of 12 inches has an R-value of 1.28, on average.

Concrete Block Insulation

• Concrete block insulation involves adding foam insulation to each individual block used in the construction of the house. Made from polystyrene, polyurethane or polyisocyanurate, this foam is either injected or poured into the central hollow of the concrete block, either as a liquid that expands and hardens, or as foam beads. This results in an R-value of between 1 and 2, on average.

Insulated Concrete Forms

• Insulated concrete forms have insulation materials built into the fabric of the house at the construction stage. Foam boards -- and reinforcing steel struts -- are installed as part of the wall and then concrete is poured around them. The wall can then be covered with wood or another traditional material so that it looks like any other home. This is one of the most effective methods of insulating a home, with an average R-value of 17.

After Construction

• A concrete cavity wall can be insulated after construction, by blowing in a loose-fill insulation material through small holes in the wall. The most common materials for use in this instance are cellulose, with an average R-value of between 3.6 and 3.8; fibreglass at an average of between 3.7 and 4.3; and rock wool, which averages between 3.1 and 4.