Wednesday, August 9th, 2017
Your home is where you grow your family, make memories and welcome friends. Nothing should stand in the way of that. When you think of your baby practicing tummy time or spending time around the dinner table, the last thing you should be thinking of is how your crawl space can negatively affect your family and the time spent together. Learn more about the Stack Effect and what this means for your home.
As warm air rises in a home, it leaks out of the upper levels. New air must enter to replace the air that escaped. In fact, in a tight home, about half of the air escapes each hour out of the upper levels. This creates a suction at the lower levels to draw in replacement air. In older homes that aren’t sealed as well, the air exchange rate can be as high as two air exchanges per hour.
This is called the ‘stack effect‘ and it creates airflow in your home from the bottom to the top. So air flow from your crawl space is drawn upwards into the first floor (living area), and then the second floor. Of course, it dilutes with other air in your home, but building scientists say that up to 50% of the air you breathe on the first floor is air that came from your crawl space. If you have hot air heating with ductwork, the air mixes even more thoroughly throughout the house.
Therefore, whatever is in your crawl space air is in the living area of your house and could be negatively affecting your home and family. If there is high humidity down there, there is higher humidity upstairs than there would be otherwise. If there are mold spores in the crawl space, there are mold spores in the living area of the home. If there are damp or musty odors in your crawl space, there is likely dampness in the living area.
This is where crawl space vents come into play. The idea is that we put in foundation vents and expect the air will flow in through vents on one side of the home and out through the vents on the other side. Unfortunately, this is false. What actually happens is 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 your home.
How does air get from the crawl space and into the home above (besides ducting)? Air is a very small thing. With this driving mechanism, (the suction of the house on the ground) air is drawn up through every tiny opening between the crawl space and your home. Holes around wires and pipes. Joints in floorboards, space around access hatches and through duct chases. You can seal these openings, but you can never get it perfect, so you cannot stop the stack effect from happening.