What is R-Value?
The Metric That Controls Your Wallet
It stands for "Resistance." Specifically, resistance to heat flow. Here is why this single number determines whether you freeze or sweat.
Imagine wearing a t-shirt in a snowstorm. You're cold because your body heat escapes rapidly through the thin fabric. Now imagine putting on a thick down jacket. You're warm because the jacket traps your body heat.
R-Value is the "down jacket" rating for your house.
The Physics of Heat Flow
Thermodynamics has one golden rule: Heat always moves from warm areas to cool areas.
- In Winter, the heat from your furnace tries to escape into the cold attic.
- In Summer, the scorching heat from the sun radiates through the roof into your cool bedroom.
Insulation acts as a barrier to this flow. The higher the R-Value, the slower the heat moves.
The Golden Rule
Doubling the thickness of insulation generally doubles the R-Value. However, the energy savings follow a curve of diminishing returns. Going from R-0 to R-10 saves a fortune. Going from R-50 to R-60 saves pennies.
Common R-Values per Inch
Not all materials are created equal. An inch of pink fiberglass is not the same as an inch of high-tech foam.
| Material | R-Value per Inch | Best Use |
|---|---|---|
| Blown Fiberglass | 2.2 - 2.7 | Attic floors (Budget) |
| Cellulose | 3.2 - 3.8 | Attic floors (Eco-friendly) |
| Spray Foam (Closed) | 6.0 - 7.0 | Roof decks, sealing gaps |
How Much R-Value Do You Need?
This depends entirely on your Climate Zone. The Department of Energy recommends higher R-Values for colder climates.
For example:
- Miami (Zone 1): Needs ~R-30 to keep heat out.
- Minneapolis (Zone 6): Needs ~R-60 to keep heat in.
Not sure which zone you are in?
Calculate Your Required R-Value Now