R-Values & U-Values…what does it all mean?

Hand in gloves holding mineral wool, building under constructionBy Ryan Davies
Energy and Customer Services Supervisor

While I am in the field performing energy audits and inspections, I frequently receive questions about those magic letters that keep your house warm in the winter and cool in the summer.  Those magic letters I am referring to are R & U Values, but what do they stand for?

R-Value is a measure of thermal resistance, or the ability of an object or material to resist the flow of heat.  U-Value is a thermal transmittance, or the heat loss through a structural element.  Most notably we see R-Value used as a rating on insulation, and U-Value (or sometimes U-Factor) represented as a rating on windows and doors.

While they are technically very different, in terms of energy efficiency they are used in the same context.  Both R-Value and U-Value are used as ratings.  The greater the R-Value of the product, the better the ability of the product to resist the flow of heat which translates into a warmer home in the winter and more consistent interior temperatures in the summer.  The opposite is the case for U-Values, a smaller U-Value is better at reducing heat transfer.

Over the years the building industry has changed, and society has realized the importance of better insulation and windows.  In 1992, the State of Oregon increased their energy code to a level where homes are “weatherized” at the time of construction.  This means homes built after 1992 have a sufficient amount of insulation and windows that have a good overall U-Value.

So let’s put this into perspective.  Currently, Energy Star recommends the following minimum levels of insulation for our climate zone in Central Oregon.  This is represented below, along with the existing conditions of a typical home you might see in Central Oregon built before 1992.

  • Energy Star Standards
    • Attic: R-49 to R-60
    • Floor: R-25 to R-30
    • Walls: R-21
    • Windows: U-0.30
  • Typical Central Oregon Home (Pre-1992)
    • Attic: R-19
    • Floor: No insulation in floor cavity
    • Walls: R-11
    • Windows: U-0.70

If your home was built before 1992, it could benefit from adding insulation or upgrading windows.  CEC offers a Weatherization program to eligible members to help pay for a portion of the improvement.  If you are interested in the weatherization program, and your home was built prior to 1992, CEC also offers a free energy audit.  The energy audit is a great starting point to determine existing conditions of the home and potential eligibility within the weatherization program.

To learn more, CEC’s Weatherization Program.