A material’s R-value is the measure of its resistance to heat flow. The way it works is simple: the higher the R-value, the more effective it is, the more the material insulates. The R-value of thermal insulation depends on the type of material, its thickness, and its density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added. It is important to know the R-value because many provinces, states or regions require that a roof system have a minimum amount of thermal resistance on commercial, industrial, and/or institutional buildings. House Insulation should be purchased based on its R value, not thickness or weight.
The effectiveness of an insulated ceiling, wall or floor depends on how and where the insulation is installed.
- Insulation which is compressed will not give its full rated R-value. This can happen if you add denser insulation on top of lighter insulation in an attic. It also happens if you place batts rated for one thickness into a thinner cavity, such as placing R-19 insulation rated for 6 1/4 inches into a 5 1/2 inch wall cavity.
- Insulation placed between joists, rafters, and studs does not retard heat flow through those joists or studs. This heat flow is called thermal bridging. So, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself. That is why it is important that attic insulation cover the tops of the joists and that is also why it is recommend to use insulative sheathing on walls.
Some quick facts about R value are:
- One type of insulation maybe thicker or thinner, but if the R value is the same they should insulate equally.
- The average recommended R value for basement insulation in
- The R value is substantially lowered if there is any air or water/moisture leaks.
- The standard R value for house insulation varies based on climate and temperature
- 1 inch of insulation is equal to 30 inches of concrete.
There are different types of house insulation materials, each having a different R value.
Some of the best insulation materials are:
- House Insulation R value of Blown in Cellulose Insulation is 3.70 per inch
- House Insulation R value of Fiberglass Insulation is 3.14 per inch
- House Insulation R value of Expanded Polystyrene is 4.00 per inch
Protecting Your House Insulation and its R value 
Protecting your house insulation and keeping your R value high is extremely important. Water is one of the biggest concerns in regards to R value and house insulation. If moisture/water gets into your house insulation, it lowers the R value. The moisture will weigh down the insulation leaving gaps and bare spots.
R-value Home Insulation Tips It's important to remember when buying home insulation, that the home insulation materials with the highest r-value may not be the most cost-effective. When insulating your basement wall to an r-value of r-12, it might be less expensive to use 2 layers of home insulation materials with an r-6 r-value rating instead of 3 r-4 r-value rated home insulation materials.
Another home insulation tip is to buy your home insulation based on its r-value not its weight or thickness. The last and most important tip for home insulation is to protect your insulation from water and moisture. Just 4% moisture in your insulation can reduce the thermal efficiency, in that area, by up to 70%.
R-Value Table
| Material | R/ |
| Fiberglass Batt | 3.14 |
| Fiberglass Blown (attic) | 2.20 |
| Fiberglass Blown (wall) | 3.20 |
| Rock Wool Batt | 3.14 |
| Rock Wool Blown (attic) | 3.10 |
| Rock Wool Blown (wall) | 3.03 |
| Cellulose Blown (attic) | 3.13 |
| Cellulose Blown (wall) | 3.70 |
| Vermiculite | 2.13 |
| Autoclaved Aerated Concrete | 1.05 |
| Urea Terpolymer Foam | 4.48 |
| Rigid Fiberglass (> 4lb/ft3) | 4.00 |
| Expanded Polystyrene (beadboard) | 4.00 |
| Extruded Polystyrene | 5.00 |
| Polyurethane (foamed-in-place) | 6.25 |
| Polyisocyanurate (foil-faced) | 7.20 |
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