Choosing the Insulation

• 1). Measure the distance between your attic rafters from the center of one rafter to the center of the next rafter. The standard rafter spacing distance is 16 inches, but some older homes may have rafters with 24 inch spaces.
  
  
• 2). Subtract 1 inch from that number to determine the width of insulation you'll need. For rafters set on 16-inch centers, you'll purchase 15-inch bats.
  
  
• 3). Determine the required depth of insulation. Rafters are generally constructed from 2-inch by 4-inch lumber or from 2-inch by 6-inch lumber. By measuring the inside width of a rafter, you'll know the bat thickness you'll need.
  
  
• 4). Choose the appropriate R-value. Insulation is rated by a numerical code that indicates how much it resists thermal transfer, or "thermal resistance." The higher the R-value, the more efficient the insulation is at reducing energy loss.
  
  

Installing the Insulation

• 1). Measure from the bottom of a rafter space to the top of the rafter space and cut a section of insulation batting the same length with the utility knife.
  
  
• 2). Position the batting in the rafter space with the paper side facing you. The side with bare insulation fibers will face the exterior of the roof. The bat is lightweight and it should fit snugly into the rafter space.
  
  
• 3). Unfold the paper edging from both sides of the bat and extend it over the adjacent rafters. Staple the paper edging to the face of the rafter approximately every 2 feet.
  
  
• 4). Locate outlets or utility boxes, if applicable, beneath the installed batting and use the utility knife to cut the batting around the boxes, removing the insulation from the top and wedging the small section behind the box if space permits.
  
  
• 5). Repeat with every rafter space until you've installed all the bats. When you're finished, the attic rafters will no longer be visible under the paper covering.