Ideas for an Energy Efficient Foundation

Converting a damaged foundation to an energy efficient foundation can incorporate a variety of inexpensive fixes or major capital improvements. For most of us, once our foundation is complete and the home is built, there is not much more we can do to the structure of the foundation without heavy equipment. That's why getting it done right the first time around is important. BUT, there are still many fixes we can make ourselves on the interior part of our foundations and basements that will improve living conditions, and the longevity of our homes.

My goal in this section to show a few examples of foundation problems for basements and crawl spaces and what can be done to convert each into a more energy efficient foundation. I will not be prescribing the improvements as much as demonstrating them. Unfortunately, there is very little "wow factor" for foundations - they are the unsung heroes of homes - but swimming pools and home theaters in basements are pretty cool...I guess it's all about "accessorizing".

Like attics, basements and crawl spaces fall into one of three categories:

  • Unconditioned - no heating or cooling energy goes into the space from mechanical systems or the building. A space is unconditioned if it does not house ducts or plumbing and has insulation against the living space.If the space does have ducts or plumbing, they should be insulated as well. In other words, an unconditioned space should not be a separate barrier without exchanging any heat or cooling to the conditioned spaces.
  • Unintentionally Conditioned – ducts and pipes are un-insulated and there is little or no insulation against the living space (usually the floor).The fix for this is to weatherize by sealing any cracks and gaps (weatherize), and insulate the interior perimeter and flooring. This creates a conditioned space that is no longer in contact with the outside or the ground, creating a more energy efficient foundation and home.
  • Conditioned – the space is part of the living area or is sealed off from and insulated against the outdoors and the ground

A crawl space or “half basement” is usually five feet or less from floor to ceiling. Heating, cooling, hot water, electrical, and plumbing systems are often placed here.

This is a classic example of an un-intentionally conditioned crawl space. Note the falling batt insulation and the uninsulated ducts. Up to half of the heating and cooling energy purchased from the utility company can be lost here from un-insulated ducts.

The inadequate insulation under the floor of the living area also contributes to energy waste. 

Another all-too-common sight: A poor insulation job that accomplishes next to nothing in energy savings and poses some safety issues to boot. Dirty insulation batts usually indicate moisture issues. In fact, in this picture, the dark culprit is most likely mildew/mold.

Fixing this problem may or may not be hard. You can rip out all the damaged insulating batts and re-insert new ones making sure that they are fastened completely and seamlessly to seal air and moisture out. More easily said than done, since the paper must be on the upper side (touching the wood). Guy Marsden from has suggested using twine that is stapled to the rafters in a zig-zag pattern.

Generally, implementing vapor barriers in unconditioned basements is challenging. One way Guy has suggested in dealing with moisture is to install 2mm clear poly up against the ceiling between the joists by stapling it to the sides about half way up. It gets very tricky to do this around the plumbing and wiring though.

This may be more work than most people are willing to invest. Along the line of the 2mm poly, you can experiment with spray foam to seal the cracks. I don't think using "great Stuff" is cost-effective, but you can rent the spray foam machine or buy foaming seal in bulk with the applicator from the web. This is a time consuming ordeal also, but it deals with moisture issues pretty well.

Intentionally Conditioned Fully Finished Basement - There are many Basement finishing systems on the market that can transform a dank, dark unused basement into a real man-cave, entertainment space or a luxurious guest suite. Just remember that if you don't already have plumbing in the right place for a bathroom or kitchen, putting one in later is very labor-intensive, my euphemism for expensive. My suggestion for a comfortable finished basement is to make sure you have done everything you can afford to start out with an energy efficient foundation as your slate. You can always stage the upgrades down the line.

Unintentionally Conditioned Basement - not quite heating the outdoors, but pretty close. Here, the mechanicals are working extra hard to not only condition the required spaces, but also the basement. The simplest fix is to install pipe insulation, duct insulation, and a hot water heater blanket; all very cheap to buy and do yourself - on the order of $100. In fact you make back the cost in your heating bill savings in a few months.

If you want to go the extra mile, caulk all holes and openings, point all the cracks, and consider fastening insulating foam board to the side walls of the foundation (make sure they are clean and mold-free first); If you decide to do this, make sure you take temperature or infrared camera readings of the walls and interior space before and after the boards are up (especially during the winter). You will be AMAZED at the results.

Here’s an excellent alternative to turning an unintentionally conditioned space into an unconditioned space, resulting in a highly energy efficient foundation:


Energy exchanges freely through the uninsulated floor of the living area; also note the open vent to the outside on the right.


After insulation and air sealing, the crawl space is now conditioned and no longer thermally in contact with the outdoors or the ground.

You can view several other foundation pictures that identify problems and suggest solutions compiled from past work. Click on my guide to perform a visual audit of your home foundation.

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