How to Determine R Values for Insulation


Most homeowners start thinking about how well their home is insulated two times a year. In autumn with winter approaching and early summer when the heat begins to build signaling its just a matter of time before the air conditioning kicks in. Anytime the furnace or air conditioner is running means lots of dollars are going to be owed to the utility companies at the end of the month. Its a known fact that to bring down heating and cooling costs add more insulation.

Things You'll Need

  • Flashlight
  • Safety glasses
  • Ruler
  • Screw driver
  • Small crow bar
  • Identify what kind of insulation is installed. The three most common types are loose fiber insulation made out of fiberglass, cellulose or rock wool. Granules of vermiculite, perlite or batting made from fiberglass.

  • Take a ruler, and measure the depth of the insulating material. If the insulating material is loose fiber multiply the depth in inches by 3 to calculate the total R-value. If granule insulation is present multiply the depth in inches by 2.7 to determine R-value. For fiberglass batting multiply the thickness in inches by 3.2 to determine the R-value.

  • Remove the socket cover from an interior outside wall, and shine a flashlight into the crack around the box to see if there is insulation. Identify what type, and use the same calculations as in Step 1.

  • Remove a section of siding and check to see if there is any insulation sheathing underneath. Depending on the climate zone the house is in if insulation sheathing is present, it will have an R-value ranging between R-2.5 and R-6.

  • Check for insulation in crawlspaces, floors over unheated garages, and unfinished basements. If you find insulation most likely it will be fiberglass batting. Look to see if the R-value is labeled on the batting. If not then measure the thickness, and multiply by 3.2 to determine R-value.

Tips & Warnings

  • Do spot checks like this throughout the house. Just because there is insulation in one area of the house doesn't necessarily mean its every where or the same type of insulation especially if the house has been added on to over the years.
  • If foam board insulation or sprayed-on foam insulation is located anywhere in the house measure the thickness of the insulation and multipy by 5 to calculate the R-value.
  • When removing outlet covers make sure you use proper precautions. Be safe. Turn off the power to the outlet first.

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