Intro - Materials - Safety - Prep - Attic Preparation - Ventilation - Rafters - Floors
Insulating the Rafters
Margin of Error: Fill entire cavity and plug holes exactly
Working on your knees in an attic for long periods of time can be very hot and tiring. You will be covered from head to toe in clothing and gear. Plan for a few breaks in your work schedule, and try to work early in the morning before it gets too hot. It may help to add a spray container of cold water to your toolbox - to spray yourself and your fogged-up goggles. You might even consider taking salt tablets. Check with your doctor to see if they might be necessary.
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Begin by measuring the length of each space. Cut each piece of insulation an inch or two longer than needed, to assure a snug fit. Use your straightedge to compress the insulation before cutting. Use a very sharp utility knife to assure a good straight cut across the fiberglass batt. Staple it to the rafters or scabbed-on boards with a staple gun so that the paper backing is toward the interior of the room, to act as a vapor barrier. Use 3/8" heavy-duty staples every six inches. Attach the insulation to the rafter scab board by the paper flange so as not to compress the fiberglass. Make sure the paper flange and the staples lie flat against the board, to create an even surface for attaching the finished wall material. A time- and work-saving aid here would be an air compressor with a staple gun attachment. It can be rented, if you don't have access to one.
Where the spacing of the rafters is uneven, odd-angled, or not standard, you will need to cut the insulation to fit. Cut it 1" wider than the necessary width, and tuck the fiberglass in to create a flange for stapling. Once the insulation is in place between all the rafters, I suggest you staple up a vapor barrier of 6 ml. visquine (a painter's drop cloth) over the insulation and across the face of the rafters. Although the paper or foil backing of the insulation is a vapor barrier, the added visquine covers completely, with no breaks. This assures that no moisture will form in the cavity. As you staple the vapor barrier to the rafters, draw it as airtight as possible. But be careful not to puncture the plastic unnecessarily as you put it in place. Should this occur, repair it with duct tape.
When installing insulation over wires, pipes, or fire blocking, it will be necessary to back cut the batt to fit over the obstacle, leaving the paper intact and the insulation uncompressed.
Tip: When installing insulation, wear clothing that fully covers your body, and consider a tetanus booster and salt tablets.
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