Many homeowners searching the internet for crawlspace repair information end up in home repair forums. While there is some good information out there, there are many examples of bad and outdated advice to repair a wet crawlspace. I have witnessed first-hand the results of unprofessional crawlspace repair and would like to set the record straight on what I consider to be some of the wrong ways for repairing a wet crawlspace.
Old building codes and bad advice have resulted in homeowners adding more exterior vents to their crawlspace in order to dry the high moisture content in their crawlspaces. The thinking behind ventilation was that air circulation would force the moisture in the crawl space air to end up outside. Through trial and error, it has been proven that warm, humid outdoor air brought into a crawlspace through foundation vents in the summer, leads to increased moisture levels. This is due to the crawlspace air being cooler than the outside air which causes the warm air to release vapor as condensation. Also, the air movement in a home does not move side to side through the vents, but instead upwards through something known as the “stack effect”. This stack effect draws air inward from every crawl space vent and up into the living space of the home. A properly closed off, mechanically vented and heated crawlspace is the only solution to reduce high moisture levels.
2. Spray Foam on a Damp Crawlspace Foundation Wall
In a dry below-grade crawlspace, this method is the most energy efficient. The problem is that in most below-grade crawlspaces, the foundation or ground floor of the crawlspace is not dry. In fact, most of the crawlspaces I run across with spray foam added as a fix have some form of dry rot in the structural components because the foam has trapped the moisture in the wood. Sill plate/rim joist repairs are needed if the original plates are untreated. It is not uncommon to see that the spray foam has even become separated from the wall from the moisture intrusion. Unless a crawlspace has external footing drains, a foundation waterproofing membrane, a foundation sealant, positive grade, and downspout extensions, I cannot ever recommend this method of insulation. Solid polystyrene insulation attached to the interior foundation wall, along with a proper vapor barrier across the entire crawlspace floor area which has been sealed to the insulation will protect the home against excess moisture from entering the home.
I have not seen a single crawlspace repair error more responsible for wood rot and mold than when plastic is attached to the floor joist system. The thinking behind this is that it will potentially stop moisture intrusion of the crawlspace air from entering the wood structure. There are many problems with this thinking, but the most important to note is that most crawlspaces are vented and cooler surfaces such as duct work, pipes, and the floor itself will actually condensate in the summer. The plastic will trap this condensation up against the floor structure causing mold and wood rot to occur. Floor joist repair is commonly needed after the joists are soaked with moisture.
4. Insulating a Damp Crawlspace With Fiberglass Insulation
This is another example of outdated advice that can result in mold growth. Paper faced insulation is very conducive to mold growth. The fiberglass will absorb the moisture and smells from the air, become heavy, and fall to the ground. Worse yet, if the insulation is stapled, it will hold moisture up against the wood components of the crawlspace and rot/mold will quickly develop in the structure. The fiberglass insulation should be removed and discarded when the polystyrene insulation is installed.
Remember, all of the air in your crawlspace will end up in your house… and then in your attic. If the air has a higher than normal humidity levels it will create many issues in your home like condensation on windows, mold in various areas, musty smells in the home, and even mold build up on the sheathing in your attic. If you have concerns or questions for repairing a wet crawlspace or any other components of your home please call Discovery Inspections to get an in-depth inspection and consultation.
NEXT ISSUE: THE WRONG WAY TO REPAIR A CRAWLSPACE PART II