The R Value of Insulation of Ceilings in a Basement

R Value

• The R-value of a material is the unit that signals its effectiveness at preventing heat loss. It is calculated by dividing the thickness of the material by its thermal conductivity – a complex equation involving joules, meters squared, time and temperature. This gives a number per inch of material. The higher the number, the better the material’s insulating effectiveness.

Glass-Fiber Batts

• The most commonly-used insulation for basement ceilings is glass-fiber batts. Also known as blankets, these are cut lengths – coming either as pre-cut or on a roll so that the homeowner can cut as required – of woven glass fiber that are affixed to the ceiling. Naturally fire-resistant, they have an average R-value of between 3.14 and 4.3, depending on the density of the batt. When installing, a vapor barrier is usually placed between the batt and the ceiling. If using batts, piping and ductwork on the ceiling should also be insulated.

Rock-Wool Batts

• Batts are also manufactured from rock wool. This is a material fabricated from the byproducts of industrial processes, such as iron smelting. Rock wool has a similar R-value to glass fiber – between 3.14 and 4 per inch, depending on density. Rock wool can also be an effective sound insulator.

Sprayed Foam

• Made from polyurethane, sprayed foam insulation comes as a liquid that is applied using a pressurized air blower. The foam expands and hardens within seconds of installation and provides an effective barrier to heat, as well as air, moisture and pests. It has an R-value of 6.25 per inch. Legally, it must be covered with a fire-resistant material such as drywall.

Cellulose

• Another blown-in material used for insulation is cellulose. It is fabricated from recycled paper products such as newsprint. It is finely shredded, treated with moisture and insect resistant chemicals and applied with pressurized air. It has an average R-value of between 3.6 and 3.9 per inch.

Boards

• Basement ceiling can also be insulated with rigid boards. These boards come in a variety of materials. These include polystyrene, which have an average R-value of between 4 and 5 per inch, and polyisocyanurate, which is faced with foil, helping raise its R-value to an average of 7.2. The effectiveness of board insulation on a basement ceiling will depend greatly on the accuracy of the installation. Thus, it is recommended to engage the services of a professional installer.