How to Insulate a basement or Crawlspace
1. Basements and crawlspaces are
often the lowest location
of air entry in a home. Cold
outside air pours into any opening to replace warm house air that
leaves in the
high parts of the house. The
foundation, sill plate, and rim joist are all locations for air entry. Poured concrete
foundations are relatively
airtight, brick and block foundations less so, and stone foundations,
or dry-stacked, are often quite open to outside air.
The insulation system must be able to address air leakage
2. Basements and crawlspaces are
subject to moisture from a
variety of sources, high water table, poor drainage and condensation. Since foundation walls are
moisture and can store moisture, basements can influence the relative
of the entire house. At
a minimum, the
insulation system must be moisture tolerant.
Ideally, the insulation system is also a vapor barrier and
the moisture load in the basement.
3. Concrete conducts heat much faster
than wood. The
insulation system needs to create a “thermal break” to reduce the heat
through the foundation and through the slab.
- Premature rotting
of wood framing
- Wet insulation
- Mold growth and
poor indoor air quality
- Air infiltration
- Cold floors
- Poor energy
- High relative
humidity in the basement and the house
Do everything within your means to
keep your basement or
crawlspace dry. Install
install vapor barriers over any exposed soil, install a sump pump, and
waterproof your foundation.
at the insulation in your
basement rim joist and sill area.
the insulation sealed in place or just stuffed in place? Is there an air leak
between the sill plate
and the foundation?
your foundation insulation
especially where the foundation is exposed to the outside. Make sure that you have
insulation that can
handle moisture and is air tight.
best insulation for basement sills and the top of the foundation is
spray foam. It’s an
air barrier, vapor
barrier, high R-value thermal barrier and it adheres to uneven surfaces.
you have a stone or cement block foundation
be careful how far down you insulate the foundation walls. Many basements heat the
around the house and keep the soil from freezing.
Insulating the whole foundation right down to the floor
the soil to freeze and damage the foundation walls. Reinforced concrete
foundations in good repair should be able to handle frost action
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