A properly insulated basement can help
reduce your energy costs. However, basement walls are one of the most controversial
areas of a house to insulate and seal.
You need to carefully consider the advantages and disadvantages, not to
mention moisture control.
Advantages and disadvantages
In most cases, a basement with insulation installed in the exterior basement
walls should be considered a conditioned space. Even in a house with an
unconditioned basement, the basement is more connected to other living spaces
than to the outside. This connection makes basement wall insulation preferable
to insulating the basement ceiling.
Compared to insulating the basement ceiling, insulating basement walls have
the following advantages:
There are some basement
finishing systems available that have the insulation built into the
- Requires less insulation (1,350 square feet of wall insulation for
a 36 × 48-ft. basement with 8-ft. walls, compared with 1,725 sq.
- More easily achieves continuous thermal and air leakage boundaries
because basement ceilings typically include electrical wiring, plumbing,
- Requires little, if any, increase in the size of the heating and cooling
equipment. The heat loss and air leakage through the basement ceiling
is similar to that through the exterior walls of the basement.
These are some other advantages of insulation on exterior basement walls:
The disadvantages of basement wall insulation include the following:
- Minimizes thermal bridging and reducing heat loss through the foundation
- Protects the damp-proof coating from damage during backfilling
- Serves as a capillary break to moisture intrusion
- Protects the foundation from the effects of the freeze-thaw cycle
in extreme climates
- Reduces the potential for condensation on surfaces in the basement
- Conserves room area, relative to installing insulation on the interior
Adding insulation to the interior of the foundation is often more cost effective
for an existing building. Interior insulation has the following advantages
- Costs may exceed those for insulating the basement ceiling, depending
on materials and approach selected
- Installation is expensive for an existing building unless a perimeter
drainage system is also being installed
- Many exterior insulation materials are susceptible to insect infestation
- Some contractors are unfamiliar with proper detailing procedures that
are critical to performance
- If surrounding soil contains radon gas, the house will require a mitigation
system underneath the basement floor.
- Interior insulation is much less expensive to install than exterior
insulation for existing buildings
- Almost any insulation type can be used, giving a wider selection of
- The threat of insect infestation is eliminated
- The space is isolated from the colder earth more effectively than
when using exterior methods
- Many insulation types require a fire-rated covering since they release
toxic gases when ignited
- Interior insulation reduces usable interior space by a few inches
- It doesn't protect the damp-proof coating like the exterior insulation
- If the perimeter drainage is poor, the insulation may become saturated
by moisture weeping through the foundation walls
- Superior air-sealing details and vapor diffusion retarders are important
for adequate performance
Types of basement insulation
Once you have determined the insulation R-value you'll need for either adding
insulation to an existing basement or new home construction, you can choose
the type of insulation, including the following:
The installation of basement
insulation will depend on the type you choose and the best way to control
moisture in your particular climate.
When insulating any part of your home, you also need to consider proper
air sealing and moisture control. Moisture
control in basements is particularly important since they are notorious
for problems with water intrusion, humidity, and mold.
Finally, you need to consider radon resistance or control when installing
any type of foundation.