A Guide to Proper Attic Insulation

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Although installing insulation in an unheated attic is usually a fairly straightforward job, a variety of pitfalls await the unwary.
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Always wear a mask while installing attic insulation to prevent inhalation of fine particles.

Thinking about putting some (or some more) insulation in your attic? This guide to proper attic insulation can help.

A Guide to Proper Attic Insulation

Although installing insulation in an unheated attic is
usually a fairly straightforward job, a variety of pitfalls
await the unwary. So, with cold weather approaching in most
parts of the country, we present this Chamber of Horrors of
attic insulation mistakes, maladies, and oversights. Look it
over, and then pay a critical visit to your own
attic–if you dare.

Vent Areas Blocked in the Eaves

Don’t push batt or blanket insulation past the top plate at
the end of joist runs . . . or fold it back and up between
the rafters . . . or pour fill insulation into such areas.
If you do, you’ll obstruct the flow of air from soft-it
vents (or, in older homes, from gaps between the outer wall
and the roof). In fact, if your roof’s pitch is steep
enough to allow access to the eaves, you can install a
slanted-board baffle at the end of each joist run to
prevent insulation from clogging the area.

Holes and Gaps in the Attic Floor

Fill in the extra space around openings where pipes, ducts,
and wires enter the attic floor, using unfaced fiberglass
or caulk. Caulk nail and drill holes, as well.

Recessed Lighting Fixtures Covered With Insulation

Recessed lighting fixtures that are covered with insulation
become extremely hot and present a serious fire hazard. So
maintain a minimum clearance of three inches between
recessed fixtures and any kind of insulation. Be
particularly careful when using poured or blown-in
cellulose, which over time can drift onto recessed
fixtures. Yes, open spaces do allow some heat to enter the
attic, but the cost of the wasted heat is nothing compared
to that of a fire. Furthermore, there is an alternative:
Replace the fixtures with flush-mounted lighting.

Vapor Barrier Placed Wrong Side Up

Install foil- or paper-faced insulation with the facing
side down.
If the facing is up, moisture will become
trapped in your insulation and turn it into an ineffective
mess. If you use loose-fill insulation, you may need to
install a vapor barrier of polyethylene sheeting between
each joist run before you pour the material, or to coat the
interior ceiling below with a vapor-retardant paint.

Faced Insulation Used for a Second Layer

If you decide to add a second layer of insulation, use only
loose-fill or unfaced fiberglass. Placing a vapor barrier
on top of the original insulation will trap moisture and
render the first layer ineffective. If you can buy only
faced bans or blankets in your area, peel the backing off
before installing the new insulation over the old.

Possible Overinsulation

If you already have at least six inches of insulating
material in your attic, you’d probably be wise to take
other energy-saving measures (caulking and
weather-stripping doors and windows, installing insulation
around heating ducts and in unheated crawl spaces, etc.)
before investing in a second layer of attic
insulation. Many energy analysts say the first four to six
inches of attic insulation are ten times more
cost-effective than the second four to six inches; in other
words, for every fuel dollar you saved when you installed
the first layer, you’ll save only about a dime by adding
another layer.

Insulation Compressed and Stuffed Into Tight Areas

It’s the air trapped in insulation, rather than the
material itself, that resists the passage of heat. When
laying batts or blankets in place, push down on them only
lightly–just enough to get a snug fit between joists.
In areas where there is cross bridging, or where the space
between two joists is unusually narrow, take the time to
cut the insulation to the size needed; don’t just stuff it
into the space. If your attic has a lot of cross bridging
or hard-to-fit spaces, fill insulation may be a better
choice than bans or blankets.

Gaps and Puckers in Batt/Blanket Insulation

Be sure to install batts or blankets with care, leaving no
open space on either side or at the point where two
sections butt together. Before laying the insulation, look
for rips and tears in the facing and repair them with tape.

Loose Fill Insulation Near Attic Fan

Poured or blown insulation is subject to shifting and will
almost surely drift out of place when used near an attic
fan, creating bare or sparsely insulated floor areas. Use
batts or blankets in such areas instead.

Animal Nests

If you hear critters scurrying about in your attic, they’ve
probably set up housekeeping somewhere in your
insulation–and may very well have cleared sizable,
heat-leaking openings in the material. Evict the offenders,
repair the damage, and try to find and block or screen off
all entryways.

Mold and Mildew, Rusty Roofing Nails

These symptoms suggest that your attic isn’t adequately
ventilated–a condition that causes insulation to
become wet (and therefore worthless) and, ultimately, leads
to wood rot in roof decking and framing. Replace any matted
insulation, check to be sure all vents are clear, and
install additional roof or gable vents if necessary.

Most experts recommend a minimum of one square
foot of free vent area for every 300 square feet of attic
floor space. Ideally, 50% of the venting is positioned low
at the eaves, and the remaining 50% higher, at the roof,
ridge, or gable ends. If you have air-conditioning or live
in a humid region, or if you’ve elected not to use a vapor
barrier between your ceiling and attic insulation, you’ll
need twice as much venting–a minimum of one square
foot for every 150 square feet of attic floor.

Uninsulated Attic Hatch

Before you cast an approving eye over your new insulation
job and climb out of the attic, be sure to cover the hatch
itself with rigid foam board insulation or a leftover
fiberglass bats, cut to size and glued in place. It’s also
a good idea to put adhesive-backed foam weather stripping
around the inside of the molding that the trap door rests
on when it’s closed, or to simply seal around the door with
duct tape.

Installer Tired, Impatient, Uncomfortable

Insulating an attic can be hot, unpleasant work in cramped
quarters, but since the care with which you install your
insulation is as important as the insulation itself, it
pays not to rush through the job. To make things easier,
insulate only on cool, cloudy days. Fear gloves,
loose-fitting clothing, a dust mask, and if you wear contact
lenses-safety goggles. Take frequent breaks. And when you
finish for the day, take a hot shower followed by a cold
rinse, to flush insulation fibers from your skin and pores.

For an overview of the various kinds of home insulation
and their applications, see “Know Your Insulation” on pages
54 through 56 of MOTHER EARTH NEWS NO. 78. An excellent and sensible
manual on cost conscious home energy conservation is

Stop Burning Your Money: The Intelligent Homeowner’s Guide
to Household Energy Savings, by John Rothchild (Random.
House; $15.50).

Is Your Attic Well Insulated? Here’s an Easy Test

Researchers at the Center for Energy and Environmental
Studies at Princeton University have devised a simple way
for you to determine whether excessive amounts of heat are
leaking into your attic.

Climb up into your attic on a cold winter evening and leave
a thermometer there for an hour or so. Then note the
reading and compare it to [1] the outside temperature and
[2] the temperature downstairs in your living quarters. If
your attic is more than 10 degrees Fahrenheit warmer than the outdoor
temperature, or if it’s closer to the temperature inside
than outside, you can figure something’s amiss.

That doesn’t necessarily mean, however, that you don’t have
enough insulation in your attic–any of the other
problems outlined in this article could be the source of
the heat loss. Check for installation flaws and heat leaks
first–then consider adding new insulation.