Crawlspaces / Basements

Residential Foundation Insulation:


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.

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.   

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.

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.

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.


 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.

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.

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.

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.


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.

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.

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.

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.

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, Tennessee, and Mississippi, 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.

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

It can happen. Avoid ……and always follow the insulation and damp-proofing manufacturer’s instructions. 

What about water proofing?  Often waterproofing is required instead of damp-proofing if the wall is adjacent to habitable space. Manufacturers of some foam products offer specific recommendations for waterproofing of their foam systems. 

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.

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. 

Will insulating the foundation increase the risk of radon problems?  Radon is not generally an issue in the Memphis area.  That being said, 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. 

Should crawl space be ventilated? Generally, one square foot of crawl space ventilation is required 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 ½ 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.

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.

Note: The Information contained within this website is for informational purposes only. Reprinted from website at The Home Inspection Company.  Memphis Inspections Service always recommends that a qualified expert be consulted in the area of concern.


Radon is a carcinogenic gas that is hazardous to inhale. Build-up of radon in homes is a health concern and many lung cancer cases are attributed to radon exposure each year. About 12% of lung cancers and more than 20,000 Americans die of radon-related lung cancer each year. The Surgeon General of the United States has issued a Health Advisory warning Americans about the health risk from exposure to radon in indoor air.  Dr. Carmona, the Nation’s Chief Physician urged Americans to test their homes to find out how much radon they might be breathing.  He also stressed the need to remedy the problem as soon as possible.

You cannot see, smell, or taste radon. But it still may be a problem in your home.  When you breathe air containing radon, you increase your risk of getting lung cancer.  In fact, the Surgeon General of the United States has warned that radon is the second leading cause of lung cancer in the United States today.  If you smoke and your home has high radon levels, your risk of lung cancer is especially high.

Testing is the only way to find out your home’s radon levels. EPA and the Surgeon General recommend testing all homes below the third floor for radon. If you find that you have high radon levels, there are ways to fix a radon problem. Even very high levels can be reduced to acceptable levels. Radon has been found in homes all over the United States. It comes from the natural breakdown of uranium in soil, rock and water and gets into the air you breathe. Radon typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. Radon can also enter your home through well water.  Your home can trap radon inside.

Any home can have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements. In fact, you and your family are most likely to get your greatest radiation exposure at home. That is where you spend most of your time. Nearly 1 out of every 15 homes in the United States is estimated to have an elevated radon level. Elevated levels of radon gas have been found in homes in your state.

EPA’s Radon Testing Check List:

  • Notify the occupants of the importance of proper testing conditions. Give the occupants written instructions or a copy of this Guide and explain the directions carefully.
  • Conduct the radon test for a minimum of 48 hours; some test devices have a minimum exposure time greater than 48 hours.
  • When doing a short-term test ranging from 2-4 days, it is important to maintain closed-house conditions for at least 12 hours before the beginning of the test and during the entire test period.
  • When doing a short-term test ranging from 4-7 days, EPA recommends that closed-house conditions be maintained.
  • If you hire someone to do the test, hire only a qualified individual.  Some states issue photo identification (ID) cards; ask to see it.  The tester’s ID number, if available, should be included or noted in the test report.
  • The test should include method(s) to prevent or detect interference with testing conditions or with the testing device itself.
  • If the house has an active radon-reduction system, make sure the vent fan is operating properly.  If the fan is not operating properly, have it (or ask to have it) repaired and then test.

If your home has not yet been tested for Radon have a test taken as soon as possible. If you can, test your home before putting it on the market.  You should test in the lowest level of the home which is suitable for occupancy. This means testing in the lowest level that you currently live in or a lower level not currently used, but which a buyer could use for living space without renovations.

The radon test result is important information about your home’s radon level.  Some states require radon measurement testers to follow a specific testing protocol.  If you do the test yourself, you should carefully follow the testing protocol for your area or EPA’s Radon Testing Checklist.  If you hire a contractor to test your residence, protect yourself by hiring a qualified individual or company.

Many states require radon professionals to be licensed, certified, or registered.  Most states can provide you with a list of knowledgeable radon service providers doing business in the state.  In states that don’t regulate radon services, ask the contractor if they hold a professional proficiency or certification credential.   Such programs usually provide members with a photo-ID card, which indicates their qualification(s) and its expiration date.  If in doubt, you should check with their credentialing organization.  Alternatively, ask the contractor if they’ve successfully completed formal training appropriate for testing or mitigation, e.g., a course in radon measurement or radon mitigation.

If you are thinking of selling your home and you have already tested your home for radon,  review the Radon Testing Checklist to make sure that the test was done correctly.  If so, provide your test results to the buyer.

No matter what kind of test you took, a potential buyer may ask for a new test especially if:

  • The Radon Testing Checklist items were not met;
  • The last test is not recent, e.g., within two years;
  • You have renovated or altered your home since you tested; or
  • The buyer plans to live in a lower level of the house than was tested, such as a basement suitable for occupancy but not currently lived in.

A buyer may also ask for a new test if your state or local government requires disclosure of radon information to buyers.


Radon Myths and Facts

MYTH: Scientists are not sure that radon really is a problem.

FACT: Although some scientists dispute the precise number of deaths due to radon, all the major health organizations (like the Centers for Disease Control and Prevention, the American Lung Association and the American Medical Association) agree with estimates that radon causes thousands of preventable lung cancer deaths every year. This is especially true among smokers, since the risk to smokers is much greater than to non-smokers.

MYTH: Radon testing is difficult, time-consuming and expensive.

FACT: Radon testing is easy and inexpensive. 

MYTH: Radon testing devices are not reliable and are difficult to find.

FACT: Reliable testing devices are available from qualified radon testers and companies. 

MYTH: Homes with radon problems can’t be fixed.

FACT: There are simple solutions to radon problems in homes. Hundreds of thousands of homeowners have already fixed radon problems in their homes. Radon levels can be readily lowered for $800 to $2,500 (with an average cost of $1,200)..

MYTH: Radon affects only certain kinds of homes.

FACT: House construction can affect radon levels.  However, radon can be a problem in homes of all types:  old homes, new homes, drafty homes, insulated homes, homes with basements, and homes without basements.  Local geology, construction materials, and how the home was built are among the factors that can affect radon levels in homes.

MYTH: Radon is only a problem in certain parts of the country.

FACT: High radon levels have been found in every state. Radon problems do vary from area to area, but the only way to know your radon level is to test.

MYTH: A neighbor’s test result is a good indication of whether your home has a problem.

FACT: It’s not. Radon levels can vary greatly from home to home. The only way to know if your home has a radon problem is to test it.

MYTH: It’s difficult to sell homes where radon problems have been discovered.

FACT: Where radon problems have been fixed, home sales have not been blocked or frustrated. The added protection is some times a good selling point.

MYTH: I’ve lived in my home for so long, it doesn’t make sense to take action now.

FACT: You will reduce your risk of lung cancer when you reduce radon levels, even if you’ve lived with a radon problem for a long time.

MYTH: Short-term tests can’t be used for making a decision about whether to fix your home.

FACT: A short-term test, followed by a second short-term test* can be used to decide whether to fix your home. However, the closer the average of your two short-term tests is to 4 pCi/L, the less certain you can be about whether your year-round average is above or below that level. Keep in mind that radon levels below 4 pCi/L still pose some risk.  Radon levels can be reduced in most homes to 2 pCi/L or below.

Contact Info

Memphis Inspections Service, LLC
2270 Riverdale Road
Germantown, TN 38138
Telephone: 901-734-0555
Fax: 901-205-0589