|All Wrapped Up
7 tips to keep in mind when
retrofitting your old house with insulation.
Keeping warm in an old house can be tricky business.
Houses built before 1940 were rarely insulated, and if they were
the products originally used may have settled or deteriorated over
time, allowing heat to escape and the cold air to creep in. I grew
up in an 1880 Queen Anne in Newton, Massachusetts—a balloon-framed
house with very little insulation. I remember those icy January
days well. When I complained that the house was too cold, my father
would simply reply, “Put a sweater on.” There’s
better advice available than my father dished out. Today there are
loads of energy-saving, cost-effective thermal insulating options
on the market, and choosing what is appropriate for your house depends
on several factors. Here are some tips to guide you through your
old-house insulation project.
to consider insulating in your old house
|Places where you may be losing heat in your
Illustration Courtesy of Rob Leanna
1 How do you decide
whether you need insulation?
First determine if you have insulation. It’s easy to confirm
whether or not you have attic insulation—usually loose fill
between ceiling joists or exposed batts of colored fiberglass. You
can also check your exterior walls for a series of patched holes.
This is a tell-tale sign of blown-in insulation.
Old houses can be drafty places, and warm air can leak from a multitude
of areas. Check and see where you may be losing heat in your house.
Chimneys and fireplaces without working dampers are typical. Other
areas to consider are air leaks though cracks around windows, ducts,
electrical outlets, and recessed lighting. Note that the primary
site of heat loss is through the top of the house. Heat rises and
can escape though roofs that are not adequately insulated.
2 What do you do with existing insulation?
A friend reopened sealed pocket doors on the top floor of his 1900
triple-decker in Boston recently and from inside the walls—along
with the pocket doors—came shredded paper. In the late 1800s
primitive insulation could be comprised of a number of mundane materials,
such as newspaper, wood shavings, corncobs, and even seaweed. Mineral
wools—substances like rock slag “spun” into fibers—were
also installed in houses as early as 1875 and are still in use today.
These early materials can be left in place.
The insulation materials introduced in the mid-20th century containing
asbestos and urea-formaldehyde, create the most concern in old houses
today. Asbestos was a common component of heating system insulation
by 1910, and by the 1930s it was also being added to some building
insulation products. If you suspect your home has insulation containing
asbestos, a known carcinogen, have the material tested. Complete
removal of this insulation would be too invasive to most old houses
so it should be left alone—unless your project is a total
rehab and you’ll be removing walls and ceilings. If the asbestos
is flaking, you can encapsulate the material—remember asbestos
fibers are a health concern only when airborne. (See “Testing
for Asbestos,” OHJ November/December 1997.)
Urea-formaldehyde, a combination of resin, hardener, and compressed
air developed as an insulation material in the 1970s, was foamed
into closed wall spaces. It was largely discontinued in the 1980s
due to concerns of off-gassing as the product cures, but today we
have a better understanding of the product and that the amount of
vapors produced is finite. After the initial curing the material
will not off-gas, unless it comes in contact with water or moisture,
then it can break down and begin off-gassing once again. You can
have your home tested for these vapors by an environmental company
in your area.
3 What form of
insulation do you use?
Building insulation can be classified into four general categories:
loose fill (cellulose, mineral, or glass fibers); batts (fiberglass,
cotton, or various wools); rigid boards (composed of plastic foams
or glass fibers); expanding sprays (proprietary systems). Batt and
rigid insulation typically come into play during a major restoration
that requires replacing walls or when you are installing insulation
in unfinished spaces such as attics.
The most common insulation retrofit for old houses is loose fill
because it can reach places where it’s difficult to install
other insulation. It also has the least effect on existing finishes.
The National Park Service (NPS) recommends using loose-fill cellulose
(recycled newspaper) insulation that has been treated only with
borates as a fire retardant, rather than insulation treated with
ammonium or aluminum sulfate. “Insulation treated with sulfates
reacts with moisture forming sulfuric acid, which can cause damage
to most metals (including copper plumbing and wiring), stone, brick,
and wood. Borates are physically and chemically compatible with
many existing old-house materials,” says NPS Preservation
Brief # 03.
4 How much insulation
do you need for your house?
An insulation’s R-value—the material’s thermal
resistance or resistance to heat flow—depends on what region
of the country you live in and what part of the house you are insulating.
The higher the R-value the better the material insulates. R-values
range from zero to 18 and more—the smaller value appropriate
for warm weather places, such as Florida, the high value appropriate
in chilly climates, such as Chicago. The Department of Energy has
a Web site that shows what the R-value should be for your region;
5 Where do you
This answer will vary from old house to old house. As mentioned,
most heat loss is typically through the roof. Since warm air has
a tendency to rise and cool air to fall, insulating the attic is
the place to start. If the attic is unfinished the insulation should
be installed on the floor. If the attic is used as a living space,
say a home office or play room, the insulation should be placed
between the rafters. One of the biggest mistakes here is installing
insulation without a proper ventilation path between the insulation
and the building exterior. Don’t block the soffit, ridge,
or gable vents in the roof. This can create moisture problems.
Thermal insulation should never be placed around old wiring. Have
an electrician check to see if the electrical insulation on your
wiring is up to code. The National Electrical Code recommends against
blown-in or batt insulation around old knob-and-tube wiring, which
could prevent heat dissipation from the electrical conductors and
start a fire.
6 How do you limit
When retrofitting an old house with insulation, one of the most
important points is to avoid creating moisture problems. Mold growth,
peeling paint, and even rotting wood are all signs of high moisture
levels. In northern climates, moisture from living spaces (cooking,
bathing, etc.) can cause problems when it migrates into walls and
condenses in insulation, especially during cold weather. As the
moisture collects, it can cause loose fills to settle or create
other problems. To avoid this, the insulation’s vapor barrier
should be facing in toward the living spaces. In southern climates,
moisture problems occur in the summer months when moist air from
the outside migrates into the building. In these cases there is
controversy over where to place the vapor barrier. Consult your
insulation manufacturer for the proper placement.
7 Are there alternative green insulation
There are a number of environmentally friendly insulation products
on the market.
Blown-in cellulose insulation made from 100 percent recycled newspaper
and treated with borates for fire-resistance and protection against
insects is labeled by the Environmental Protection Agency for effectiveness
against termites, cockroaches, ants, earwigs, and many other insects.
This product contains no free formaldehyde, no ammonium sulfate,
no fiberglass, and no asbestos.
Another product winning green accolades in the market place is
polyisocyanuate, a rigid material that per thickness has a higher
R value than batt or blown-in fiberglass, cellulose, and cotton
insulation. Polyiso also provides an effective moisture barrier
when used with laminated aluminum foil facers in masonry cavity
wall applications. This type of insulation can be installed between
furring strips when the walls in your house need to be replaced
altogether. Another green insulation product is cotton insulation
made from recycled denim; this product is itch-free and easy to
install. It is also treated with borates to keep insects away.
An early insulating material still on the market today is Homasote
fiber board, which consists of 100 percent recycled newspaper mixed
with a small amount of other ingredients, including paraffin wax
as a water repellent and copper metaborate for resistance to fungi,
termites, and carpenter ants. It’s a great soundproofer, and
although it has an R-value of only 1.2, South Pole explorers in
the 1930s and ’40s lined their buildings with it.
Environmental Home Center
(800) GET Pink
Polyisocyanurate Insulation Manufacturers Association