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Introduction:
 | Homes being constructed today are more energy efficient than those
built even just a few years ago, primarily due to significant improvements
in building products and techniques as well as development of
high-performance heating and cooling systems and other appliances.
However, the benefits of foundation insulation are often overlooked. Heat
loss from an un-insulated, conditioned basement may represent up to 50
percent of a home's total heat loss in a tightly sealed, well-insulated
home. Foundation insulation is used primarily to reduce heating costs and
has little or no benefit in lowering cooling costs. In addition to
reducing heating costs, foundation insulation increases comfort, reduces
the potential for condensation and corresponding growth of mold, and
increases the livability of below-grade rooms.
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Foundation types:
| Foundations are either full basement, slab-on-grade, or crawlspace.
Deep frost lines and low water tables often make a full basement the
primary foundation of choice. However, home additions often have
crawlspace foundations.
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Full basements:
| Basements can be insulated either on the interior or exterior.
Interior insulation can use conventional 2´4 framing with batt or
wet-spray insulation. Unless the vapor retarder covering on the batt
insulation is fire rated, it should be covered with drywall. Rigid foam is
also used on basement interiors. Furring strips are used to hold the foam
insulation in place. Extruded polystyrene expanded polystyrene, or
polyisocyanurate insulation boards can also be used. Fire codes require
most foam insulation board to be covered with dry wall.
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| Exterior foundation insulation uses extruded or expanded polystyrene
directly on the outside of exterior basement walls. Insulation exposed
above grade must be covered to protect it from physical abuse and damaging
effects of the sun. Typical cover materials include roll metal stock to
match the siding, cementous board attached to the sill plate, or
application of a stucco like finish.
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| A third option is to use a foam-form foundation system. Polystyrene
foundation forms are set on conventional footings, much like building a
Lego's® wall. Concrete is placed into the forms where it cures to form
both the structural and thermal components of the basement wall. Exterior
foam, either foam boards placed on the exterior of a conventional
foundation or in a foam form wall system, may provide a concealed entry
path for subterranean termites. Termites can tunnel through and behind
many foam products. If exterior foam insulation is used, a continuous
metal termite shield must be used between the top of the foundation and
the sill plate to force termites out of the foam and into view. Even then,
treatment with conventional termiticides to stop the infestation may be
difficult. Foundation waterproofing, site and footing drainage, and
termite treatments are similar for insulated and un-insulated basements.
However, if exterior foam insulation is to be used, use waterproofing
products compatible with the foam.
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Crawlspaces:
| In many respects, crawlspace walls are just short basement walls.
Exterior foam and foam-form insulation systems can be used. However,
interior crawlspace wall insulation is usually either foam board or draped
insulation. If foam insulation is used, it extends from the top of the
foundation to the top of the footing. The cavity formed by the rim joist
should be filled with fiberglass batts or a foam-in-place product. Most
fire codes allow up to two inches of polystyrene exposed on the interior
of a crawlspace before covering is required.
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| If crawlspaces are insulated with fiberglass or mineral wool batts,
the batts are usually tacked to the sill plate and draped down and onto
the floor. Four foot- wide batts incased in a plastic cover work well when
installed horizontally. Conventional 16- or 24-inch-wide batts leave voids
between the batts and do not perform as well.
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| Some jurisdictions require a ventilated crawlspace to help control
moisture. Vent requirements are significantly reduced if the floor of the
crawlspace is covered with plastic sheeting with joints overlapped and
taped to reduce crawlspace moisture. If required, install operable vents
so they can be closed. Don’t forget to fill the rim joist space with
fiberglass batt or foamed-in-place foam to complete the insulation
treatment.
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| The floor over the crawlspace can also be insulated. This raises the
thermal envelope from the crawlspace walls to the space floor. While this
technique offers many advantages, piping must be freeze proofed and
heating and cooling ducts must also be insulated.
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Slab-on-grade:
| Heat loss is greatest at or near the exterior grade. To reduce heating
costs and reduce the cold-floor syndrome common to slab-on-grade
construction, insulation is critical. Exterior foam insulation, similar to
exterior basement insulation, works well. Insulation should extend from
the top of the slab to the top of the footing. Foam insulation inside the
footing is also common. It is necessary to provide a thermal break to
prevent thermal wicking from the slab to the outside. Installing a
pressure-treated nailer or beveled slab edge provide the thermal break
while still allowing floor-covering attachment. Climate, cost of fuel,
efficiency of heating equipment, and type of foundation determine the cost
effective level of insulation.
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| Savings from insulated foundations vary with fuel price, heating
equipment performance, and climate. The cost of full-basement foundation
insulation will vary but builders have reported prices between $800 and
$1,200. If the mortgage of a new home were increased by $1,200, the
increase in home payment would be $106 annually for a 30- year, 8% loan.
The combined heating and mortgage costs would be similar and the home
would be more comfortable and provide a healthier indoor environment.
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Frequently Asked Questions:
If a basement is unfinished does it still need foundation insulation?
| Yes, unless the floor above is insulated. Even if used only for
storage and heating and cooling equipment the basement is thermally
connected to the rest of the house. |
Is floor insulation above a basement or a crawl space an alternative
to foundation insulation?
| Yes, but keep in mind that pipes, ducts and HVAC equipment located in
the basement would then need to be insulated to meet the MEC and to
protect pipes from freezing. Sometimes these can be grouped in a small
area with insulated walls while the floor above the rest of the basement
is insulated. |
Doesn’t placing insulation on the exterior improve energy performance?
| If the basement incorporates passive solar design with a significant
amount of south facing windows, exterior insulation will be beneficial,
provided the walls are exposed to solar gain. In a typical basement the
energy savings are negligible. |
Should the interior of foundation walls have vapor barriers?
| If interior insulation is used, YES. The concrete must be allowed to
dry, but moist basement air typical of Midwest summers should not be
allowed to reach the cool wall where in can condense. Batt insulation
specifically designed for the interior of foundation walls has a
perforated poly facing that prevents air from circulating through the batt,
but allows water vapor from the wall to escape.
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Will foundation insulation increase the risk of termite entry?
| Foundation insulation does not increase the risk of termite entry. If
termites are present in the soil and wood is used in the building, the
risk of infestation exists. Exterior insulation may reduce the probability
of early discovery and inhibit treatment when discovered.
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Is an inspection band where foundation insulation is omitted to permit
inspection for termites a good idea?
| In some southern states with a high incidence of termite infestation,
including, Florida, South and North Carolina, Georgia, Alabama,
Mississippi, Louisiana, eastern Texas, southern and central California,
Georgia, Tennessee, and Hawaii, rigid foam insulation is not allowed in
contact with the soil. In other areas a six inch gap between the top of
foundation insulation and any wood framing member is required to permit
visual inspection for termites.
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Will exterior foundation insulation materials be chemically attacked
by damp-proofing?
| In can happen. Avoid ……and always follow the insulation and
damp-proofing manufacturer’s instructions.
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What about water proofing?
| Codes often require waterproofing instead of damp-proofing if the wall
is adjacent to habitable space. Manufactures of some foam products offer
specific recommendations for waterproofing of their foam systems.
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How long will exterior foundation insulation last?
| Properly installed foundation insulation, interior or exterior, should
last as long as insulation installed any where else in the building.
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Should foam insulation above grade be protected?
| Foam above grade must be protected from both sun and physical damage.
Ultraviolet light degrades or destroys most foams. In addition, damage
from lawnmowers, balls, and other incidental contact can degrade the
appearance and performance of the foam. Common materials used to protect
the foam above grade include two- or three-layer stucco finishes, brush-on
elastomeric or cementitious finishes, vertical vinyl siding, cement board,
aluminum coil stock, and fiberglass panels.
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Will insulating the foundation increase the risk of radon problems?
| Radon entry into a home is through cracks and other opening below
grade. The use of foundation insulation should minimize thermal stresses
on the foundation and help minimize cracking, thus reducing of radon
entry.
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Should crawl space be ventilated?
| The CABO One and Two Family Code requires one square foot of crawl
space ventilation for each 150 square feet of “floor” area. Operable vents
1/10 as large can be used if a vapor barrier is installed. Warm damp
summer air can condense on the cool earth, even when covered with a poly
vapor diffusion retarder, increasing the risk of crawl space moisture
problems. Installing a vapor barrier and closing the operable vents is
preferred. If local code interpretation requires crawl space ventilation,
insulating the floor and incorporating a vapor barrier is preferred. |
Do foam insulation boards installed on the interior require fire
protection?
| All foams require thermal protection equal to ˝ inch of gypsum wall
board when installed on the interior of a building, including a crawl
space. The only exception is Celotex Thermax
polyisocyanurate which may be installed without a thermal barrier where
approved by the local building code official.
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Are insulating concrete form (ICF) systems less expensive than an
insulated poured in place concrete wall?
| ICFs can be competitive but costs are project specific. Foam used in
these systems should address the same concerns outlined above for foam
board.
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