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How to Insulate Small Areas

Henri Bauholz

Every insulation project has a few places where the standard-sized rolls of insulation will not fit. To make certain that your home is completely insulated, you will have to cut and fit pieces of insulation to completely fill the irregularly shaped areas.

  1. Put on all work clothes and safety gear. This includes your work gloves, safety glasses and dust mask. For this task you will want to purchase a rubber or plastic mask with an interchangeable filter. Do not use the old paper masks.

  2. Examine the places between the framing members (this includes rafters, floor joists, wall studs and places around windows) and make sure there is no air leakage from outside. Also check for water stains (if you find water damage, the time to deal with that problem is right away). Also you can remove any loose debris that you find in the wall or roof cavities (i.e. between the rafters or wall studs).

  3. Make sure that you have insulation on hand that is of the correct width and thickness. Rolls of fiberglass insulation usually come in two widths, 22 1/2 and 14 1/2 inches. These sizes can be used for walls or rafters that are framed at 24 or 16 inches on center. Also, insulation comes in various thicknesses beginning at 3 1/2 inches and going all the way up to 11 1/4 inches. Most likely when you are insulating small areas you will be finishing off an insulation job (usually in the attic), so the insulation will already be on hand.

  4. Narrow spaces in the wall or roof can be filled by making a cut lengthwise along the piece of insulation. Cut the piece extra wide by 1 inch so that you can staple both edges of the insulation to the wooden rafter or wall stud. The preferred method is to staple the paper backing of the insulation to the inside surface of the framing member, though some prefer to stretch each piece of cut insulation across the front edge of each wall stud or roof rafter.

  5. Fill the irregular spaces that are created when two parallel rafters meet a diagonal ridge line of a hipped roof or dormer. You will find a lot of spaces like this in your attic, especially if you have a hipped roof. This will be the simplest task, for you should be able to use the entire width from a roll of insulation material with just a diagonal cut at one end.

  6. Fill a triangular shaped area by measuring the opening with a tape measure and then transferring the measurements to the paper side of a piece of insulation. Again add 1 inch to any cut you make into the insulation batt so that it can be securely stapled to a framing member.

  7. Fill any narrow cracks between two boards by simply pushing a thin sliver of insulation into the space. Don't forget that compressing fiberglass insulation into a tight space does not increase the insulation value but rather causes a slight decrease. Insulation works best when it is allowed to be completely unrolled and fluffed up to its proper size.