How to Insulate an Old Attic

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Of all the areas in a home to be insulated, the attic is the most important. In the winter, valuable heat escapes from the living spaces below. In summer, the sun heats the attic and makes the house difficult to cool. The U.S. Department of Energy (DOE) states that heating and cooling "account for 50 to 70% of the energy used in the average American home." Insulation amounts are measured in R-values: the higher the value, the more effective the insulation. Local building codes may regulate the minimum R-value for your area. You can insulate with unfaced fiberglass batts, or use a machine to blow in loose cellulose fill.

Things You'll Need

  • Measuring tape
  • Ladder
  • Flashlight
  • Dust mask
  • Safety goggles
  • Expanding foam spray
  • Polystyrene roof baffles
  • Staple gun with staples
  • Insulation (batts or bags of loose cellulose fill)
  • Blower machine
  • Utility knife
  • Wire mesh
  • Tin snips
  • Scrap wood
  • Saw
  • Hammer
  • Power screwdriver and screws

Determine Your Attic's Needs

  • Go into your attic and check for existing insulation. If there are planks on the the joists, you have the option of pulling them up to install batts or drilling holes in the wood and blowing cellulose beneath them.

  • Use the measuring tape to measure the depth of the joists. If your attic has existing insulation, measure the depth of the insulation as well.

  • Measure the attic floor square footage (length x width of the perimeter).

  • Contact your local codes department to determine the recommended insulation R-value for existing homes in your region.

  • Purchase the amount of insulation you will need to cover the attic floor at the required R-value depth.

Insulating with Fiberglass Batts

  • Seal off all air leaks. Spray the expanding foam into all holes and cracks on the attic floor. Do not spray foam into ventilation areas such as ridge vents, soffit vents or gable vents.

  • Insert the polystyrene roof baffles between the roof rafters, in the eaves. This will allow proper ventilation through the soffit vents. Staple the baffles in place.

  • Measure the first section of batting; cut the batting with your utility knife.

  • Carefully and snugly fit the batts in between the joists. Do not compact the batts into place, as this will reduce the insulation's R-value.

  • Cut sections of wire mesh with the snips. Fit the wire mesh around all electrical fixtures in the attic floor, to maintain several inches of clearance between the fixture and the insulation. Staple the mesh into place, if necessary. Cut the insulation to fit around the mesh baffles.

Insulating with Blown-In Loose Fill

  • Seal off all air leaks: spray the expanding foam into all holes and cracks on the attic floor. Do not spray foam into ventilation areas such as ridge vents, soffit vents or gable vents.

  • Insert the polystyrene roof baffles between the roof rafters, in the eaves. This will allow proper ventilation through the soffit vents. Staple the baffles in place.

  • Find all electrical fixtures installed in the attic floor. Measure and cut segments of scrap wood to surround the fixtures, allowing 3 inches clearance between the fixture and wood. Screw into place.

  • Have a helper dump the first bag of cellulose fill into the blower machine. Take the blower hose, and move to the far end of the attic.

  • Direct your helper to turn on the blower. Aim the hose at the back corners first, and work your way toward the attic opening.

Tips & Warnings

  • If you are blowing in insulation, it is best to have a helper feed the machine with cellulose while you blow the insulation into the attic.
  • Do not install insulation on top of old knob-and-tube wiring, as this is a fire hazard. Check with your municipality concerning code regulations for insulating around old electrical wiring.
  • Wear long-sleeved pants and shirt to protect your skin from irritating insulation fibers.
  • If you have chosen fiberglass insulation, use only unfaced fiberglass batts. Unfaced batts allow moisture to escape, whereas paper or foil facing traps moisture and can lead to rot or mildew problems.
  • Never cover soffit vents with insulation.
  • Keep all insulation at least 3 inches away from chimneys, stovepipes, and any heat-producing equipment.
  • If the insulation depth rises above the height of the attic floor joists, do not replace or install attic subflooring; the weight of the flooring will compact the insulation and sharply reduce its effectiveness and R-value.

References

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