Tech Brief 13
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Concrete Basements
Basements are a valuable part of any new home, with benefits far outweighing
cost. About half of all new homes in North America are built
with basements, and the rest could be. Concrete is the material
of choice for basement construction, with 98% of North American
basements built of one of many available concrete wall systems.
Why build a basement?
Basements provide inexpensive space for many uses. A basement’s
sturdiness and location make it
ideal for housing mechanical equipment like furnaces, water heaters
and other utilities. These same
properties make it an excellent choice for recreational space,
storage areas, workshops or hobby
rooms. Basements typically house main electrical lines, plumbing
and ductwork, making these easily
accessible for changes and repair. The sheltering properties
of below-grade space make basements “safe havens” for
occupants during hurricanes, tornadoes and severe
thunderstorms. With a few upgrades,
basements can be transformed into
entertainment centers, offices or extra
bedrooms for a growing family. This
provides a homeowner future expansion
potential without the cost of constructing
more floor space above ground, and can also
substantially increase the resale value of a property.
How much does basement space cost?
Building almost any home requires digging, from a few inches to a
few feet. By increasing the
digging to 6–8 feet, forming walls of the desired height, and
pouring a concrete slab at the bottom,
a contractor can make a foundation into a full basement. The
incremental cost can be as little as
$10 per square foot over the cost of a shallower, stem wall foundation,
or $20 per square foot
over the cost of a simple slab on grade—far below the cost of
constructing more space in the
above-ground portions of a house.
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Why is my basement built of concrete?
For basement construction, concrete is by far the product of choice.
Concrete provides a permanent,
stable base for a house to rest on and creates an enclosed space
protected from the ground, rodents
and weather. Sturdy concrete walls are highly resistant to shifting
or sagging under ground and
water pressure, often for a century or more. When necessary, strength
can be enhanced by increasing
wall thickness and embedding steel reinforcing bars inside the
concrete. Concrete does not rot, warp,
rust, deteriorate or provide a food source for mold in the presence
of water or moisture. Concrete
doesn’t burn and can’t be eaten or damaged by termites, insects
or vermin. Properly designed
concrete walls keep out water, radon and outside noise. They can
also be constructed with a
durable architectural finish and high insulation value.
What are the different ways to build my basement out of
concrete?
Cast-in-place concrete using removable forms
(sometimes called “poured concrete”) produces an
economical wall with a hard, durable surface on
both sides. Concrete masonry (block) walls can
also provide an architectural surface in many
different colors and textures, for a distinctive exterior
appearance and an attractive interior finished wall.
Insulating options are available for both cast-in-place
and masonry wall systems, depending on desired
results. Insulating concrete forms (ICFs) create a
highly energy-efficient wall that is ready to finish
with traditional gypsum wallboard on the interior
surface. Solid precast panels are also pre-insulated, ready for
wallboard, and go up rapidly in almost any
weather. Some precast panels have insulation “sandwiched” into
the center of the wall, providing a
smooth finish that doesn’t require wallboard. Autoclaved aerated concrete
(AAC) blocks are made of
a lightweight concrete with good insulating properties.
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What should I look for to
be sure I'm getting a quality basement?
Experience counts—As with any construction, it is important to hire
a reputable, experienced
contractor. Look for someone with a history of building with the
type of system you desire. Check
references to verify quality workmanship and professional performance.
Water
management—In many areas it is necessary to install components
that keep ground water
away from the perimeter of a home. Talk with your contractor about
a damp-proofing or waterproofing
membrane over outside walls and a drainage system at the base of
the foundation. Waterproofing
membranes offer superior performance over damp-proofing products
and are readily available.
Plan ahead—If you are planning to use the
basement for storage, work or living space, inspect the
plans to make sure ceiling heights are adequate and mechanical
equipment is located out of the way.
Quality control—When construction
is complete, check that all basement dimensions match those
on the plans. Walls should be straight and precisely vertical.
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What's the bottom line?
A basement provides valuable, versatile space for a new home at a relatively
small additional cost.
Concrete creates strong, high-quality walls, with different systems
offering a variety of properties to
meet your needs. For best results, retain a reputable and experienced
professional contractor. Plan
your space with an eye toward future use. Look for proper water
control measures, and verify that
the results match your plans.
For More Information
To learn more about concrete
basements, visit:
Autoclaved Aerated Concrete Products Association, www.aacpa.org
Concrete Foundations Association, www.cfawalls.org
Insulating Concrete Forms Association, www.forms.org
National Concrete Masonry Association, www.ncma.org
Precast/Prestressed Concrete Institute, www.pci.org
Concrete Homes Helpline: (888) 333-4840
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