Preparation - Installation - Mistakes
Fiberglass insulation commonly comes in 3 1/2" and 6" thick rolls. It can be applied in double layers to increase it past 6 inches. It is available in widths to fit between 16" or 24" on center framing members. It comes in two forms: Batt and Blanket. Batt insulation is available in 4' or 8' lengths. Blanket insulation is usually 56' long when 3 1/2" thick and 32' long when 6" thick. We recommend blanket insulation as there are fewer gaps between pieces.
Fiberglass is available in foil-backed, paper-backed and un-faced batts and blankets. Both the foil and paper act as vapor barriers. The foil, however, is only of value when used in conjunction with a 3/4" air space. Un-faced fiberglass is used in conditions of potential fire hazards and as the top layer of a two layer application.
- Have a pencil and paper and a trouble light with an extension cord before going up to your attic. Carefully examine your attic space before you begin. Determine whether you will be using the space for living and want to heat it or prefer to just insulate the main part of the house below the attic.
- If you wish to finish and heat the attic space, look closely at the rafters, checking them for depth and uniformity. They must be adequate to house the depth of batting needed for your area. Furring out the rafters to the proper depth will also give you a point of attachment for the vapor barrier and a structure capable of supporting finishing material like drywall or paneling.
- Some rafter systems are not deep enough to accept fiberglass batting and/or even enough to attach a vapor barrier or support a finished wall of paneling or gypsum board. Attaching scabbed on boards to the existing rafters will fir them out to an even depth. Nail up a set of reference strings on the rafters that protrude the most into the attic. Stretch the strings across the face of the rafters to show you the proper depth to which you want to align the scabbed on 2 " x 4" boards.
- Jot down the required lengths of each board. Measure and mark the boards with a steel tape measure and cut them to length with a circular saw . Cut all the boards at one time. Make the cuts in the attic if possible to avoid unnecessary trips up and down the stairs.
- Position each board against the rafter and align it with the string. Nail it firmly into the existing rafter. Use 6d nails every 16".
- Continue this process until the entire rafter system is scabbed out to accommodate the insulation.
- Complete your preparation by attaching flexi-vent material (a waffle-like strip of plastic) designed to allow air circulation to carry away moisture that would build up between the roof and the new insulation. Butt the strips right up next to each other and against the roof itself.
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