BK Home Inspections > Blog > Basement Q&A > Master Home Inspector Frequently Asked Questions: Foundations

Master Home Inspector Frequently Asked Questions: Foundations

As a Master Home Inspector I get lots of questions from individuals about insulation and their home’s foundation. Here are a few great questions along with the answers I share with inquiring home owners to help them save money and protect their home and their family.

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 crawlspace an alternative to foundation insulation?

Yes, but keep in mind that pipes, ducts and HVAC equipment located in the basement would also need to be insulated 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.

Does 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 however, 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 it 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.

Will foundation insulation increase the risk of termite entry?

Foundation insulation does not increase the risk of termine 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.

It is a good idea for the purposes of foundation inspection for termites to allow an open band or a small area where foundation insulation is omitted?

In some southern states with a high incidence of termite infestation, including Florida, North and South Carolina, Georgia, Alabama, Mississippi, Louisiana, eastern Texas, southern and central California, Georgia, Tennessee, and Hawaii, rigid foam insulation is not allowed to come in contact with the soil. In other areas, a 6-inch gap between the top of the foundation insulation and any wood framing member is required to permit visual inspection for termites. An InterNACHI inspector can be hired to perform required pest inspections.

Will exterior foundation insulation materials be chemically attacked by damp-proofing?

In can happen. Always follow the insulation manufacturer’s instructions for damp-proofing.

What about waterproofing a foundation?

Codes often require waterproofing instead of damp-proofing if the wall is adjacent to habitable space. Manufacturers of some foam products offer specific recommendations for waterproofing their foam systems.

How long will exterior foundation insulation last?

Properly installed foundation insulation should last as long as insulation installed anywhere else in the building.

Should foam insulation above grade be protected?

Foam above grade must be protected from both sun and physical damage. Ultraviolet light degrades and 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.

Will insulating the foundation increase the risk of radon problems?

Radon entry into a home occurs through cracks and other openings below grade. The use of foundation insulation should minimize thermal stresses on the foundation and help minimize cracking, thus reducing radon entry.

Should crawlspaces be ventilated?

The CABO (Council of American Building Officials) One and Two Family Code requires 1 square foot of crawlspace ventilation for each 150 square feet of floor area. Operable vents 1/10th 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 crawlspace moisture problems. Installing a vapor barrier and closing the operable vents is preferred. If local code interpretation requires crawlspace 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 ½-inch of gypsum wall board when installed on the interior of a building, including a crawlspace. The only exception is Celotex Thermax™ polyisocyanurate, which may be installed without a thermal barrier where approved by the local building code official.

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.

In summary, taking time to plan the best insulation system for you new home, and taking stock of the insulation currently installed in your home, can lead to energy savings in the long run.


Bob Beisbier, owner of BK Home Inspection, is a Certified Master Home Inspector who has been providing professional and thorough home inspections in southeast Wisconsin for over 12 years. Bob is Infrared certified, DILHR Certified, and provides Home Energy Tune-ups, Environmental Data Reports, Pre-sale Home Inspections and Pre-offer Home Inspections.