As you may recall from the first part of this lesson, R-value is a wall's capacity to resist heat loss or its thermal resistance. Insulation materials are rated in terms of their R-value, with a higher R-value indicating better insulating effectiveness.
The R-value of thermal insulation depends on the type of material, its thickness, and its density. Generally, walls are not made up of just one material or one layer.
R-values for most commonly used building materials are given in the table below. From looking at the table below, we can see that natural materials like stone and bricks are not good insulation materials, but most of the synthetic insulation products such as polystyrene or polyurethane are very effective insulation materials.
|Material||R-Value (ft2 o Fh / BTU)|
|Plain glass, 1/8 inch||0.03|
|Stone per inch||0.08|
|Common Brick per inch||0.20|
|Asphalt Roof Shingles||0.44|
|1/2 inch Gypsum Board (Drywall or plasterboard)||0.45|
|Wood Siding, 1/2 inch||0.81|
|Plywood, 3/4 inch||0.94|
|Insulating sheathing, 3/4 inch||2.06|
|Fiberglass, per inch (battens)||3.50|
|Polystyrene per inch||5.00|
If insulation materials have a low R-value per inch, then they will need to be thicker than those materials with a higher R-value per inch to achieve the same degree of effectiveness in resisting heat loss.
Look at the chart below to compare the thickness required of various insulation materials to achieve the same R-Value of 22 and then answer the questions below.