How to insulate attic trusses

Updated February 21, 2017

Attic trusses fit the width and span of your roof. Unlike a standard stick-frame roof, which is open beneath the rafters, trusses have support rails that run at angles from the bottom of the truss to the top and sides of the truss. Because of this, you can't finish out your attic, but you can insulate it to reduce your energy bills.

Cut batt insulation to fit along the roof eave. This is the narrow wedge area at the edge of the attic where the roof meets the attic floor.

Position one insulation batt along each eave, but don't force it back into the narrow wedge space. The batt will serve as an insulating barrier that blocks the blown-in insulation from filtering into the vents in the eave.

Block around can lights by cutting a circle 4 inches larger than the diameter of the can from an insulation batt. Place the hole in the batt around the can. Center the batt so the insulation is at least 2 inches away on all sides from the can. Use a utility knife to cut out the shape.

Place a lightweight scrap of thin drywall or plywood over every can light to keep blown-insulation from filtering next to the cans.

Block around any type of heat vent that runs through the attic, such as the chimney of a wood stove. You may use drywall or plywood. Cut pieces to form a barrier around the pipe. Keep the block at least 8 inches away from heated pipes on all sides. Check local building code to determine the exact distance required in your community.

Measure from the drywall between the trusses up to the desired insulation height and make marks on a few trusses with a pencil. Determine this measurement by the degree of insulation you want. Look at the chart on the insulation bags to determine how many inches you must blow in to obtain the desired insulating factor. These marks will serve as a visual guide when blowing in the insulation.

Start at the perimeter of the attic and turn the blower on. The insulation fibres will shoot out, but not with force. Move the hose back and forth to distribute the fibres lightly and evenly between the trusses. Use an assistant to feed insulation continuously into the hopper unit, positioned on the floor below the attic.

Work your way toward the attic access hole. When you near the hole, step down on the ladder and add more insulation around the hole.

Cut a piece of batt insulation to fit over the inside of your attic access door, since that spot is tough to reach with blown-in insulation.


Wear a full respirator, protective eyewear, and pull on disposable coveralls over your clothing. A hat that has a wide brim increases visibility, since it catches the fibres that fall directly in front of your face.


Step on the trusses as you walk about the attic. The only thing separating the attic from the room below is a layer of drywall and it won't hold your weight.

Things You'll Need

  • Blow-in insulation
  • Insulation blowing rig
  • Batt insulation
  • Utility knife
  • Scrap plywood or drywall
  • Full respirator
  • Hat with brim
  • Protective eyewear
  • Disposable work coveralls
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About the Author

Glenda Taylor is a contractor and a full-time writer specializing in construction writing. She also enjoys writing business and finance, food and drink and pet-related articles. Her education includes marketing and a bachelor's degree in journalism from the University of Kansas.