Attic Insulation 5 - Attic Preparation

Intro - Materials - Safety - Prep - Attic Preparation - Ventilation - Rafters - Floors

The attic is probably the greatest single heat loser in the home. The lighter heated air rises while the heavier cool air drops (convection). That's why your feet are usually cold or why your much taller mate says it's too hot when you want to turn the heat up.

Adequate insulation in attics is imperative. Newer homes are generally well insulated - although it never hurts to check. But many older homes have little or no insulation. Oftentimes what there is has deteriorated or compressed beyond even minimal worth.

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The most widely used insulation in the attic is fiberglass. Fiberglass commonly comes in 31/2" to 6" thick rolls. It can be applied in double layers to increase it past 6". 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 available in lengths from 30 to 70 feet in standard manufacturer's thickness. I recommend blanket insulation. There are fewer gaps between pieces.

Fiberglass is available in foil-backed, paper-backed, and unfaced 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. Unfaced fiberglass is used in conditions of potential fire hazards and as the top layer of a two-layer application. Otherwise, paper-backed is used.

Preparation

Margin of Error: Leave no gaps

Prior to actually installing the fiberglass, you need to do some preparatory work. The first thing to do is to decide how you want to utilize your attic space.

Have with you a pencil and paper, and a trouble light with an extension cord, before you go up to the attic. Carefully examine your attic space. Determine whether you will be using the space for living and therefore want to heat it or whether you prefer to insulate the main part of the house below the attic. Locate your insulation in such a way that it encloses the heated areas only.

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 for fiberglass batting, for an attached vapor barrier, or to support a finished wall of paneling or gypsum board. Attaching scabbed-on boards to the existing rafters will extend them out and increase their depth . You need to be sure these new boards attached to the rafters all come out to exactly the same level, because you need to attach your finishing material to an even surface. To do this, nail up a set of reference strings on two scab boards, one on each end of the attic roof. Stretch the strings across the face of the rafters to show you the proper depth to align the scabbed-on 2 x 4 or 2 x 6 boards.

Jot down the required lengths of the boards. 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 R firmly into the rafter, using 16d nails every 16". Continue this process until the entire rafter system is scabbed out to accommodate the insulation. Be sure all scab boards come right to the reference strings.