Why Insulate Basement Walls When They Are Below Grade?

A home improvement worth sharing...

Homeowners with basements in the St. Louis area sometimes ask, why would I insulate the portions of my basement walls that are below grade? After all, if my basement walls are nine feet in height with one foot exposed above ground level and eight feet below ground, aren’t the bottom six feet or so deep enough that the temperature of the earth stays warm even during winter?

Of course it’s true the temperature of the earth in any place remains pretty much constant year round and is approximately equal to the yearly average air temperature. Here in the St. Louis area the average temperature year-round is 56 degrees. Below ground we can expect the temperature of the earth to remain a pretty constant 56 degrees.

So, if you own a home in the St. Louis area, ask yourself this question. In the winter, if I set my thermostat to a comfortable 68 degrees, am I losing heat through my basement walls to the 56 degree earth? The answer, obviously, is yes. And that costs you both in terms of money spent re-heating and in terms of comfort.

If you do not “intentionally” heat your basement, you are “unintentionally” heating it whether you want to or not.  Especially if your furnace and some or all of your ductwork is in your basement, you are losing heat before it reaches upstairs. Even without either a furnace or ductwork in the basement, heat from upstairs will reach the basement. We all know that warm air rises, but heat can travel in other ways besides air currents (think conduction and radiation).

What about the summertime?

If I am spending money to run my air conditioner and set my thermostat to 74 degrees, doesn’t the cool earth temperature of 56 degrees help the situation? If I insulate my basement walls, won’t that reduce the transfer of heat out of the house to the earth? The answer again, obviously, is yes.

What may not be so obvious in the warm-weather scenario is the fact that, in the St. Louis area, we are primarily a heating climate. This means we spend far more money over many more days heating than we do cooling. In St. Louis, when choosing home improvements that affect both winter and summer, the winter results far outweigh the summer results. This means insulation of basement walls will help much more than it hurts. The net effect is what we want it to be.

The bottom line is, insulating your basement walls in the St. Louis area can reduce your annual energy expenditures and, at the same time, make your home feel more comfortable. So why wouldn’t you?