How to Install Fiberglass Attic Insulation
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Lay down boards or plywood sheeting to help you be able to walk safely in the attic space.
Safety Tip: When installing fiberglass insulation, observe all safety precautions. Fiberglass can release tiny fibers, which can be harmful if breathed into the lungs and which may irritate the skin. Wear protective gear.
Determine the area of the space to be covered by measuring the width and length of the surfaces to be insulated. Multiplying those two numbers will result in the total square footage of the area. Compare this measurement to the recommended amount needed in your attic. The necessary R-value for the attic will depend upon the manufacturer and style of insulation chosen. Check with the manufacturer's instructions on the packaging to determine how much insulation is needed to achieve the desired R-value.
Once you've determined the amount and type of insulation needed, and the insulation has been purchased, begin staging the rolls in the attic. Place rolls around the perimeter of the attic for easier access during the installation.
When laying insulation, it's a common mistake to cover up the soffit vents. Soffits are part of the overall ventilation scheme, and covering them blocks essential air flow in the attic. To prevent that from happening, use soffit baffles. Soffit baffles are stapled right to the bottom side of the roof planking, between the rafters and above the soffit vents.
Begin laying in the insulation, starting at an area farthest from the attic access (Image 1).
When rolling the insulation, cut it to length using a utility knife.
Tip: When you reach the end of a line, pull the insulation back slightly, then place it on a joist so there is a solid surface to cut on. Using a straightedge as a guide, make your cut (Image 2).
After making the first cut, use the remaining portion of the roll and work back in the other direction. When you reach the end of that roll, butt a new roll up to the cut piece and finish the run.
Once the perimater is reached, cut the end of the roll to fit. Using this technique results in the best use of the insulation and reduces wasted material.
Tip: Lay the rows snugly together to prevent undesirable gaps or spacing.
When you run into an obstacle like a cross-brace or pipe, cut a notch in the insulation roll to fit around the obstacle, then continue with the run (Image 1).
Areas around the perimeter of some attics can be rather tight and confining (Image 2). Just keep rolling out the insulation, but don't compress or squeeze it into tight spots, as this can decrease the insulation value.
If your home has recessed lighting in the ceilings, keep insulation at least 3" from the lighting fixtures unless the fixtures are IC-rated (insulation-contact rated). Contact with a nonrated fixture could cause the fixture to overheat, causing a fire in surrounding materials. Fiberglass insulation is noncombustible, but surrounding materials such as wood, drywall or paint could catch fire.