The benefits of insulating your attic are well-known: It saves energy, cuts costs and keeps a home more comfortable. But what isn’t touted so much is that faulty installation can actually be counterproductive.
Improperly installed attic insulation can result in lower or no energy savings and a waste of your money. In some cases, improper installation can cause moisture damage to your home’s structure.
Despite manufacturers’ assertions that insulation installation is as easy as unrolling a sleeping bag, it’s actually a much more complicated process, especially in older homes.
For example, in an unfinished attic, the insulation should always be placed in the floor joists, in the space closest to the heated part of the house, says Jim Schmiedeskamp, a manager with Owens-Corning, an insulation manufacturer.
Placing insulation in the joists of the attic walls or roof, meanwhile, is simply a “gigantic waste of money” that results in no energy savings, says Al Rozo, a research architect with the University of Illinois at Chicago’s Energy Resources Center.
Furthermore, the placement of the insulation’s vapor barrier is also important. If installed wrong, the vapor barrier can cause condensation problems that can lead to rot, ceiling staining and, down the road, structural problems.
A few general facts: The most common type of insulation for attics is a blanket-a large roll of fiberglass insulation that is usually pink or yellow.
The blankets can come “faced” with a vapor barrier, usually in the form of a sheet of paper or foil adhered to one side of the insulation; or “unfaced,” without any sort of a barrier.
The blankets usually come in different lengths and, more importantly, different thicknesses, which translate into R-values.
An R-value is simply the degree to which the insulation resists heat loss. Different insulation materials have different R values per inch (even air and wood have small R values).
According to the latest U.S. Department of Energy data, the attic insulation recommendation for Chicago area houses has a value of R-38-insulation about a foot deep.
To install insulation properly, a homeowner first needs to take a good look at the attic to determine the scope of the job. Is the attic floored? Is it used for storage? And is there any insulation already in place.
You’ll also need to measure the attic-specifically, the width and depth between floor joists, the length of the attic and the depth of any existing insulation.
Best-case scenario
The best of all possible insulation jobs involves an unfinished attic with 12-inch-deep, exposed floor joists. Obviously, such an attic is not used for storage.
Carry the insulation to the attic before opening up the packaging: The compressed blankets tend to inflate once they’re out of the packaging. Use sheets of plywood to navigate yourself and the insulation over the joists.
To insulate, simply roll out the insulation into the gaps between the joists, placing the vapor barrier face down. “You always want the vapor barrier to face the `warm in winter side,’ ” says Schmiedeskamp.
Gently ease the insulation into the joist, and if the blanket is slightly wider than the gap, carefully turn up the sides of the blanket to the sides of the joists.
“You don’t need to staple or tack it down,” says Schmiedeskamp. “Just lay it down into the joists.”
Be extremely careful not to jam the insulation into the joist. “The last thing you want to do is to compress the insulation,” says Rozo. “It needs to be spongy to function properly. If you do wind up compressing it, you are reducing its R-value and essentially wasting your money.”
“If you took a 12-inch-thick blanket and compressed it to six inches, you would lower its R-value from 38 to something like 21,” says Schmiedeskamp.
Start the end of the insulation roll at the far edge of the attic near the eaves, and work your way into the center.
“Don’t push the ends of the insulation all the way to the roof line at the eaves,” says Rozo. “Keep it to where the downstairs wall ends. You need to keep the eave vents open so that the attic can be properly vented. Otherwise, you can face condensation problems in your attic.”
“Insulated attics tend to be colder than those that aren’t insulated, and moist air can condense much quicker,” says Schmiedeskamp.
Or, you can install cardboard or foam baffles that run up from the eave vents above the insulation to ensure proper venting.
To cut the insulation during installation, press down on the unfaced side with a straight-edge metal ruler and use a utility knife to cut through the compressed insulation.
If the floor joists are only six or eight inches deep, the recommendation is to fill them with exactly that much insulation, and than lay a second layer over the top of the first layer in a criss-cross pattern.
“You want the second or top layer of insulation to be unfaced,” says Schmiedeskamp.
Hence, six inches of insulation into the joists would give you an R-value of 19. Another six inches across the top of that would yield an R-value of 19, giving you a total R-value of 38.
Never place insulation around ceiling light fixtures, especially recessed or canister light fixtures. “Always allow at least three inches of space between the light and the insulation to prevent the light from overheating,” says Schmiedeskamp. “And keep the insulation at least three inches away from any metal chimneys in the attic.”
Finally, seal gaps between the attic and the floors below-such as a chase-with insulation or caulk, says Rozo. “You want to prevent a stack effect in which the attic pulls up air from the basement or a lower level, while downstairs that air is being replaced with cold air from the outside,” he says.
Floored attics
While the above type of insulation project is the easiest, it’s also usually the rarest.
To offer storage space, many attics in Chicago have flooring that allows you to easily traverse the joists. Sometimes this flooring is simply a piece of plywood laid across the joists. Other times, it is planks of wood nailed down to the joists, similar to a wood floor on a downstairs living level.
Placing insulation over an attic floor would again be a “waste of money,” says Rozo. “The gap between the downstairs ceiling and the attic floorboard creates a channel of air and a pathway for convection to occur,” he says. “To properly insulate, you don’t want any air movement. In fact, you could add 10 feet of insulation to the top of an attic floor and it wouldn’t do you any good.”
As a result, the only way to properly insulate a floored attic is to pull up the floor, the experts say, and lay down the insulation in the joists as described above.
“Once you’ve installed the insulation, you can replace the floorboards and use the attic once again for storage as long as the floorboards are not compressing the insulation,” says Rozo. “Hence, if the joists under the floorboards are only six inches deep, only fill them with six inches of insulation. Although you won’t attain the recommended R-value of 38, six inches of insulation is better than none.”
You can also try to prevent convection by blocking air passages under the floorboards, says Schmiedeskamp, by installing barriers at the end of the joists.
“You could then insulate directly above the floorboards,” he says. “But you would still have to pull them up to install the barriers.”
Existing insulation
In older homes, existing attic insulation may come in the form of loose fill or cellulose, a cotton-like material found in the joists.
It may also be found in the form of an older layer of blanket insulation, especially in newer homes.
To determine the R-value of the existing materials, simply measure it. If it’s six inches deep and is not compressed, it probably has an R-value of roughly 19. If it’s three inches deep, it has an R-value of about 10 or less.
In an unfloored attic, you can place an insulation blanket-or more loose fill insulation-on top of the existing insulation to bring it to the top of the joist. Then criss-cross it, if necessary, with another layer to bring the R-value up to 38.
“Use only unfaced insulation to avoid condensation problems,” says Schmiedeskamp.
“Try to keep the layers of insulation level as you want to avoid any gaps, which will result in convection, lowering the R-value of the insulation,” says Rozo.
If the existing insulation is a blanket, make sure any vapor barriers are pointed down toward the heated part of the home. If they’re pointed up, remove the insulation and reinstall it.
If the insulation is loose fill and is old and compressed, it’s probably not offering much in the way of R-value, says Rozo. You should consider removing it and replacing it with new insulation.
“As with any insulation work, you should be careful and wear a respirator, a long-sleeved shirt and a goggles,” he says. “Try to scoop up the old insulation with a dust shovel and place it in plastic bags.”
Then replace it with new insulation as described in the steps above.
“Overall, adding insulation is a worthwhile endeavor,” says Rozo. “And it does offer a definite payback.”
“The payback depends on a lot of different factors: how cold the winter gets, how old your furnace may be and how well-insulated the rest of your house is,” says Schmiedeskamp. “But it’s not only a good energy investment but it will make your home feel more comfortable in both the heating and cooling months.”
