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Insulating With Fiberglass

1 INSPECT YOUR EXISTING INSULATION BY MEASURING ITS DEPTH. Measure the distance between the joists so that you can buy insulation that is the right width—standard widths are 15 inches or 23 inches.

2 ADEQUATE INSULATION REQUIRES PROPER VENTING, WHICH IS USUALLY SUPPLIED BY VENTS IN THE SOFFIT. Blocking vents allows moist air to collect in the attic, causing wood rot and mildew. To avoid this, install rigid plastic foam vents, called baffles or rafter vents. Put one end over the soffit vent, and staple the baffle in place.

3 MEASURE AND CUT TO LENGTH THE PIECES OF INSULATION YOU'LL NEED. Work in a well-ventilated area to keep to a minimum the amount of fiberglass dust raised. Cut the insulation with a sharp utility knife guided by a straightedge. Have a solid work surface beneath the insulation and apply lots of pressure.

4 PUT THE INSULATION BETWEEN THE JOISTS, STARTING AT AN EXTERIOR WALL and working toward the entry to the attic. If working in an uninsulated attic, get insulation with a vapor barrier and install the barrier facedown. If you're applying insulation over existing insulation, get insulation without a facing.

5 THE NATIONAL ELECTRICAL CODE REQUIRES A 3-INCH GAP BETWEEN INSULATION AND ANY ELECTRICAL LIGHTS OR FIXTURES. Check to see if your local code is stricter. Nail wooden barriers around the light to keep the insulation away from it, then cut the insulation to fit.

6 IF THE EXISTING INSULATION FILLS OR NEARLY FILLS THE CAVITY BETWEEN THE JOISTS, you can still add more insulation by rolling it across the top of the joists, perpendicular to them.

Installing loose-fill insulation

MATERIALS: Cellulose insulation, staples, foam baffles, fiberglass insulation

TOOLS: Tape measure, hand stapler, drill and bits, insulation blower, safety glasses, dust mask, gloves, pry bar

Short of tearing off the walls, blow-in, loose-fill insulation is the only way to insulate a house built before the days of adequate insulation. You can buy fiberglass or cellulose loose-fill. Put the insulation in a blower located outside the house and stretch a hose to the area you’re insulating. The hose usually has a switch that lets you turn the machine on and off from wherever you’re working. Have a helper working outside to refill the blower with insulation.

Blowing In Attic Insulation

1 PREVENT THE INSULATION FROM BLOCKING SOFFIT VENTS by installing a rigid plastic foam baffle above each vent. If you have a continuous soffit vent, install a baffle in every third space between rafters.

2 ONCE THE BAFFLES ARE IN, block off each vent to prevent it from filling with insulation and causing moisture problems by cutting sections of fiberglass insulation and stuffing them between the joists directly in front of the soffit.

3 IF THE ATTIC HAS A FLOOR, REMOVE A BOARD to give you access to the bays between the joists. Insert the blower hose the entire length of the bay, and back it out as the space in front of it fills with insulation. [Drill through the floor if it’s plywood.) If the attic has no floor, put down pieces of plywood and walk along them as you spray the insulation in place.

4 POUR AND SPREAD INSULATION BY HAND, ESPECIALLY NEAR ELECTRICAL FIXTURES. Electrical codes require that you keep insulation at least 3 inches from heat-producing fixtures, such as recessed ceiling lights. Nail 2x blocking between the joists, positioning it to keep the cellulose away from the fixture.

Blowing Loose-Fill Into A Wall

1 DRILL ACCESS HOLES EQUAL TO THE DIAMETER OF THE BLOWER’S FILLER HOSE. If you drill the holes from outdoors, remove a piece of siding first. Pick a piece slightly above the level of the interior floor and drill holes through the sheathing. On the top floor, remove the fascia or soffit instead of the siding.

2 FILL THE BIN WITH INSULATION. Wearing safety glasses, a mask, and gloves, fill the bin to the level recommended by the manufacturer. Buy an extra bag or two of insulation just in case. You can always return the unopened ones when you’re finished.

3 USE A TAPE MEASURE TO CHECK FOR HORIZONTAL OBSTRUCTIONS, SUCH AS FIRE BLOCKS IN THE FRAMING, THAT MIGHT BLOCK THE INSULATION. If the tape hits an obstruction, first make sure it's not electrical and then drill an access hole several inches above it. When you insulate, fill the bay from both the original hole and the new one.

4 ONCE THE HOLES ARE DRILLED, INSERT THE FILLER TUBE and push it to within 18 inches of the top of the wall. Blow in the insulation, retracting the tube as the bay fills. When you've insulated the entire wall, plug the holes. Although plastic, foam, and wooden plugs are available, plastic is typically the best choice. Replace the trim or siding.

KNOW YOUR BLOWER - You can usually find insulation blowers where you buy your insulation, and you may be able to use a blower at no additional charge. Ask the salesperson to demonstrate how the blower works, and check that all of the fittings, attachments, and hoses are included.

MOISTURE MATTERS - Most insulation requires a vapor barrier on the side that is warm in the winter. You won’t need a vapor barrier in the attic as long as you have 1 square foot of ventilation for every 150 square feet of insulation. If you have less ventilation than that, paint the ceiling below the insulated area with vapor-retarding paint. Paint the walls only if the winter temperature typically drops below -15° F. Before you insulate, look closely for peeling paint, which may be a sign of existing moisture trouble. If the situation seems to get worse after you insulate—or if you see signs of trouble elsewhere—a coat of vapor-retarding paint on the inside wall should solve the problem.

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