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Dirt Crawl Space Floors - Why Construct with Dirt?

All areas of the country have a mix of crawl spaces, basements and slab on grade construction.  Crawl Spaces and basements are not different other than lower ceiling height in a crawl space, yet they are different building codes for basements and crawl spaces.

The only reason to build a home with a dirt crawl space is to save money. A dirt crawl space is cheaper than a concrete floor. If money were not an obstacle, builders could build the perfect house. But money is an obstacle. So it's pay now or pay later for homeowners. Still, the damage from having a dirt crawl space is so significant. Simply put, a house with a dirt crawl space is dysfunctional, and a dysfunctional house is not worth building at any price.

crawl space with dirt floorIf we think about how we would build a basement, the same rules should apply to a crawl space. In this day and age, we would never have a dirt floor basement so why do we have dirt floor crawl spaces? We would never vent a basement, so why vent a crawl space?

If you went down into a friend's basement in the winter, and saw a window open, or many windows open for that matter, you'd tell them to close the window. Yet we put big holes in our crawl space walls and accept it as normal in the name of making things better.

Why Care?

Many homeowners never go down into their crawl space unless they absolutely have to. They shut it out of their "often visited places in my house" list, and shut it out of their mind, like it doesn't exist.

If you care about how much you pay for heating and cooling, then you should care about your crawl space. If you care about your home rotting, or mold, allergies, or asthma, then you should care about your crawl space. If you care about the comfort of your home, cold floors, drafts, and how your home smells, then you should care about your crawl space. If you care how long the paint lasts on your house, about doors and windows sticking, about hard wood floors buckling, and about carpets going moldy, then you should care about your crawl space. If you care about your resale value, then you should care about your crawl space. You can't get away from it.

The house is one building. It operates as a system. You can't have one part of the building that is sick, and another part that is healthy. You can't rationalize that you never go in the crawl space so you aren't affected by it. Why? Simple. Air mixing.

The crawl space air is bad. It is damp. It is cold if it's winter. It is full of mold spores. It smells. And this crawl space air is in your building envelope. It gets upstairs in one of two ways the stack effect (explained below), or the HVAC system through your ducts. You are breathing it. In fact we know that 1/3 to 1/2 of the air that you breathe on the first floor of your house came through your crawl space. And this goes for basements too.

Radon gas is a naturally occurring radioactive gas that comes from the ground. For many years we have known that if you measure the radon levels in your basement or crawl space, and then measure upstairs, you will have about 1/3 the amount upstairs. Since radon only comes from the ground, this demonstrates how air moves in a house from bottom to top.

The stack effect is when warm air moves upwards in a house. This happens in summer and winter. Warm air rises because it's lighter than cold air. So when it rises, what happens? It escapes out of the upper levels of our homes. But we can't create a vacuum in our homes, so when air escapes; new air has to come in to replace the air that escaped. Where does the new air enter the house? At the lower levels. Through crawl space vents for one, and up from the earth for two.

The notion that we put in crawl space vents and air will flow in through vents on one side of the house and out through the vents on the other side is false. What really happens is that air enters the vents in the front, enters the vents in the back, and enters the vents on the sides, and then it goes up into the house.

New York Times - YOUR HOME; How to Keep Radon Gas In Check

Wikipedia - The Stack Effect