ECM: Building Envelope

B5. Install/Increase Attic Insulation


Attic insulation reduces the amount of heat that flows from a dwelling unit through the attic to the cold outside air. By reducing this heat loss, attic insulation reduces the amount of energy needed to heat the dwelling unit in the winter. In the summer, attic insulation saves on cooling costs and keeps buildings more comfortable by reducing the conduction of heat from the hot attic through the ceiling and into the unit.

A material’s resistance to heat flow is measured in units of “R-value”. The higher the R-value, the better the insulating properties. The R-value of insulation depends on the type of insulation and its thickness. Optimal R-value for attic insulation depends on the existing insulation, fuel costs, and climate.


  • Single-family and low-rise multifamily buildings with attics
  • Attics that currently have less than 12 inches of insulation


  • Batt insulation, also called rolls and blankets
    • fiberglass
    • rock wool
  • Loose-fill insulation
    • fiberglass
    • rock wool
    • cellulose


  • Insulation must be installed according to manufacturer’s directions. Unless the attic is used as a habitable space, attic insulation should be installed between the rafters of the attic floor, rather than the attic ceiling.
  • A vapor barrier must be present on the warm side of insulation to prevent moisture problems.Photo: Attic insulation can reduce both heating and cooling costs.
  • Recessed lights or fans that protrude into the attic space should not be covered by insulation.
  • Insulation should not obstruct vents or louvers.
  • Installation crews should wear protective gloves and masks.
  • Installation must comply with local fire codes.
  • Loose-fill cellulose insulation must be a fire-retardant type.


  • Installing attic insulation is relatively easy, inexpensive, and cost effective.
  • In mild climates, adding insulation where some attic insulation already exists can produce fuel savings ranging from 13 to 21 percent.


Energy Conservation for Housing – A Workbook, HUD, September 1998. Pages 7-25 through 7-28 address attic insulation, applications, and effectiveness.

Attic Insulation. Part of the U.S. Department of Energy's Consumer's Guide.

HUD Energy Efficient Rehab Advisor. Discusses Insulation Basics.

DOE Insulation Guidance. Information on insulation levels for existing and new homes from the U.S. Department of Energy.

Consumer Guide to Home Energy Savings, American Council for an Energy Efficient Economy, 1999, ISBN 0-918249-38-4. Pages 21 through 27 address attic insulation methods and strategies.

Insulation and Air Sealing. Part of the U.S. Department of Energy's Consumer Guide. Discusses both air leakage and moisture control

The Home Energy Saver. Addresses attic insulation, including strategies and effectiveness.

ENERGY STAR Program: Home Sealing. Provides information on insulation strategies, recommendations, and links to other information resources.

Simply Insulate. A website of the North American Insulation Manufacturers Association that provides a variety of information about the benefits of insulating homes. Features include installation information and tools that determine the necessary insulation in your state and your projected energy savings.