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Determine your insulation R value

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The US Department of Energy (DOE) lists inadequate insulation as a leading cause of home energy waste because it forces even the most efficient heating and cooling systems to work harder and consume more energy.[1] Properly insulating a home not only saves energy, it also maintains an even temperature throughout the house, so you won’t need your woolies every time you go to the back bedroom.

How to determine how much insulation you need

All insulation has an R-value rating, usually from R-7 to R-50. This rating indicates the insulation’s resistance to heat flow from a warm area to a cooler area—like from your toasty kitchen to the adjacent unheated garage. Insulation with a high R-value will block the heat from leaving your kitchen better than insulation with a lower number. Local building codes often specify R-values but these may be minimum values for comfort, rather than for optimal energy efficiency.[2] Before you can determine which R-value to buy, you need to answer these questions:

  • Which type of insulation will you use? Fiberglass batting or recycled denim? The R-value is based on a product’s material, thickness and density. Always look for insulation that has been certified by ENERGY STAR, GreenGuard™, Green Seal, or another reputable green product certification program.
  • Where do you live? Northern climates require insulation with a higher R-value rating.
  • What are you insulating? The attic is usually easiest to access and can accommodate thicker insulating materials than your walls.
  • Are you adding to existing insulation or are you insulating a new area? If your attic already has R-11 insulation and you want to improve the R-value to R-38, then you need an additional R-27 in insulating material. To determine the R-value of your existing insulation, use the DOE’s formula.
  • Are you insulating an existing house or are you building a new one? Typically existing structures have 2-inch by 4-inch wall framing and can only accommodate insulation that is 4 inches thick. New construction or home additions can be built with thicker walls (2-inch by 6-inch framing) to accommodate higher R-values, such as R-19 to R-21.[3]
  • How is your house heated? A house with electric baseboard heat has no heat loss through air ducts compared to a gas-heated house with air ducts in the attic. Therefore, insulation with a higher R-value may be needed in the gas-heated house.

Once you have answered these questions, use the DOE’s Zip Code Insulation Program to determine the R-value for your insulation project. This program is a comprehensive calculator that will determine the R-value specifically for your house, not just your climate zone.

Or, for a quick recommendation, try:

Determining how much insulation you need helps you go green because…

  • It ensures installation of the proper R-value for your house, thereby maximizing the building’s ability to maintain even heating and cooling temperatures.
  • It optimizes a building’s ability to reduce heat flow either into or out of the building, which decreases energy use for heating and cooling.
  • A properly insulated building uses less energy, which decreases pollution and greenhouse gas emissions associated with energy production and consumption.

The Rocky Mountain Institute estimates that upgrading insulation in just the attic of the typical American home will reduce that home's CO2 emissions by 2,142 pounds per year and save more than $116 per year in heating costs.[4] The Institute also estimates that the payback period for improved insulation is five years for homes heated with gas or oil, or that use air conditioning. The payback is shorter for homes heated with an electric furnace or baseboard heating.[5] Because proper insulation has a significant impact on a home’s energy efficiency, it can result in the need for smaller heating and cooling units.[6]

Tax breaks and incentives

In the US, upgrading your home's insulation may qualify you for tax incentives at the federal, state, and local levels. For detailed information, see these resources:

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