The Stack Effect may not have been considered...
We were recently called out to look at a crawl space that was underperforming. The Homeowner called us out because of soft, springy floors and low areas in some portions of the home floor. Additionally, there was a funky smell in the house. When we arrived, we went down into the crawl space and immediately discovered the problem. Mold was in advanced stages of attacking the wood joists and beams.
Moist air sticks to any wood surface and is condensed and accumulates there.
This crawlspace problem may be more common than people realize. Why? This comes from an error in the initial thinking and design of crawlspaces. Originally, the thinking was to ventilate the crawlspace, with vents installed around the perimeter to try and keep the space free of mold and fungi. That thinking was “bass ackwards”. Over time we began to realize the “stack effect” that draws hot air up into the attic and out the vents, will replace that air mostly from the crawl space below it.
The problem with this thinking is that wet air is sucked into the crawlspace from outside in this “stack effect” flow. Moist air sticks to any wood surface and is condensed and accumulates there. It is a phenomenon known as Hygroscopicity. Moist wood is a breeding ground for mold and fungi. Not only do these make for unhealthy even deadly air when it gets drawn into the air of the home during the stack effect, but it deteriorates the wood itself since that is what the mold and fungi use for food to grow.
This crawlspace problem may be more common than people realize.
In this particular case, the attack had been going on for a long time and was so advanced that the structural wood members had almost no strength to them. You could literally break off chunks with your bare hands and in fact our inspectors had to be really careful not to accidentally knock off or break members as they were crawling around.
How to stop it? Encapsulate the crawlspace. Seal it with a liner. Seal up the vents, seal the entry doors and any obvious points of entry. Control the crawlspace humidity with a dehumidifier. You will breathe healthier air, have lower energy bills, and most importantly, preserve the wood structure portions of your foundation and floor system.
It really does no good to replace the vertical supports in your crawl space if the horizontal members rot and fall apart since they will not be able to span between the vertical smart pier supports. More importantly, even if you replace the vertical supports and don’t protect the wood members you will likely have failure afterwards as the wood becomes lunch for mold and fungi.
It only makes sense when you are fixing the structural supports of your crawl space, to encapsulate the crawlspace at the same time.
How to do that? Stay tuned…. More to come in my next blog!
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