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Getting Adequate Attic Insulation

Attics and Basements, Heating and Cooling, Interior, Green Living, Insulation Published 02/13/2007 by Danny Lipford

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No matter where you live in the U.S., homeowners are struggling more than ever before to find the balance between being comfortable inside their homes and keeping energy bills smaller than their mortgage payment. This struggle has taken center stage as the cost of energy rose dramatically this fall and December has already produced lower-than-average temperatures to date. Although turning down your thermostat will help at first, the ultimate in energy savings is to keep the heat you’ve paid to produce within your walls as long as possible. That makes adding insulation one of the single most effective ways to save on heating costs.

In almost any climate, if you can see the tops of your attic floor joists when you venture up there, you’ll need to add more insulation. As a minimum, most home in the U.S. should have between R22 and R49 in the attic – that’s about 7 inches to nearly 12 inches. But take the time to go to the Department of Energy’s Website to get an exact minimum for where you live. The DOE Website has a wealth of easy-to-access information about saving energy that is practical and accurate.

To determine if you need more insulation, measure what’s in place with a ruler or tape measure. When you do the measuring, make sure you have plenty of light to work because you will have to walk exclusively on the top edge of the joists—let your foot slip in between where the insulation is and you will end up breaking through the drywall or plaster ceiling in the room below.

Once you determine how much insulation you have and then the amount you need, it is easy enough to install additional amounts over existing insulation yourself. There are quite a number of insulations types including rigid foams, sprayed-in foams, mineral wool, and natural products like cottons and wools, but most attics in the U.S. are insulated with either fiberglass or cellulose:

Fiberglass

Fiberglass insulation comes in rolls or batts and is formed at a particular width and thickness to fit between studs in walls or joists in attics. Each thickness represents an R-rating standard (for instance, R-19 is 5-1/2 thick for use with 2×6 wall studs or attic/floor joists).

Blown Fiberglass

This is fiberglass in a loose form that can be blown by a professional installer through a hose to whatever level is desired.

Cellulose

Cellulose is a paper-based insulation (much of it recycled newsprint) treated with fire retardant that is also blown into attics or walls with a large, vacuum-like machine.

Which material you use is less important than making sure you have enough insulation for your climate. All of the insulation types above do a good job, and you do not need to stay with the form that is in your attic now when adding more. Here are some tips that will help you add more insulation:

• If you are using fiberglass insulation in batt or roll form, make sure the insulation is unfaced—that means no kraft paper or foil facing on either side.
• Wear a long-sleeve shirt, long pants, gloves, eye protection, and a dust mask.
• If you’re using roll or batt fiberglass insulation, lay it perpendicular to the joists so it does not compress the existing insulation below it and creates a blanket with fewer areas where air can leak through from below.
• Don’t cover can (recessed) lights unless they are rated for contact with insulation. If using loose (blown) insulation, build a small enclosure with hardware cloth or plywood to keep the insulation away from lights and exhaust fans.
• Use cardboard or rigid-foam baffles to keep soffit vents from being blocked by insulation where the rafters rest on the outside walls. Encouraging this cold air circulation above the insulation will help exhaust moist warm air leaking from the living space below. If it can’t find a way out, it can condense and begin to rot the roof sheathing.
• Fill all cracks between the living area and the attic with caulk or expanding foam. This includes areas where plumbing vent pipes, flues, electrical wiring, and vent fans, and light fixtures poke through into the attic. Sealing these voids helps defeat the “chimney effect” that draws cold air in at the base of the house and exhausts warm air (that you’ve already paid to heat) out into the attic floor (the ceiling of the top-most living area of the house) at a furious pace.
• If you are insulating walls or uninsulated joists, fill the cavity completely with insulation.
• Don’t overly compress the insulation—it’s most effective in a fluffy state.
• Split or cut insulation when you run into electrical wiring across the stud or joist bay.
• In walls and floors, staple faced batts every 8- to 12- inches.