Hardwood Floor Cupping – Crawlspace Moisture Problems


Hardwood Floor Cupping Problems? Elevated Crawl Space Moisture Problems …

With the passing of Spring break, and the upcoming Easter weekend, days become longer and temperatures rise. Weather patterns change to a more sub-tropical feel. Dew point levels increase. It is the start of the condensation season inside North Carolina crawl spaces. Crawl Space construction is the most common construction type in the Southeastern United States. Many of these crawl spaces contain HVAC duct work that service the upper areas of the home. Once the air conditioning is engaged, duct work acts like a refrigerator soil causing crawl spaces to condensate at a more aggressive pace until the peak of the season in August and September. At certain times of the day, open crawl space vents can allow problematic outside air to intermingle inside the crawl space environment accelerating the buildup of moisture. This extra moisture is absorbed into the floor joists, girders, sub-flooring and insulation. Over the next several months, wood moisture levels can exceed 19% causing floor systems to swell, and hardwoods to cup. Cupping can result in an expensive repair as homeowners may need to re-sand and refinish those hardwoods based on the amount of damage incurred.

How do I stop my hardwoods from cupping if I have duct work under the house and traditional crawl space vents installed on my home?

Before spending money on unneeded repairs, there are some simple things that you can do to help with the challenge.

  • Solve all drainage and grading problems on the house.
  • Keep gutters clean.
  • Extend downspout discharge lines a minimum of 5ft from the foundation wall.
  • Keep bushes and shrubs, ivy etc. well pruned and manicured to a normal size so they don’t block crawl space vent locations.
  • Keep below grade vent wells clear of mulch, yard waste, and debris.
  • Raise the settings on the air conditioning up a couple of degrees to reduce condensation build-up.
  • Ensure all duct work is properly sealed and upgrade to new duct work if possible to improve efficiency.
  • Check for plumbing leaks annually

Once these basic home maintenance items have been completed there still may be a need for a crawl space moisture control program to be installed on the home to eliminate the excess condensation. Keep in mind that the buildup of moisture inside crawlspaces is more of a result of lack of air exchange, than moisture intrusion in many cases. Passive air movement through the crawl space vent is actually a good thing during most of the year. The problem is the air exchange during the summer is not fast enough to keep up with the buildup of moisture. Over time, the crawl space reaches 100% relative humidity, or dew point. Condensation begins to form on the duct work, insulation, floor system and other construction materials inside the space.  The tighter the crawlspace, the harder it is to move and exchange the air. As a result of this problem, there has been an explosion of crawlspace science companies presenting potential solutions to this problem. Some of these solutions can be horribly expensive and traumatic to the consumer. Some of these protocols include:

  • Encapsulations
  • closed crawlspaces with humidistat control dehumidifiers
  • forced air induction using existing HVAC equipment
  • barometrically controlled crawlspace vents
  • temperature controlled crawlspace vents
  • relative humidity controlled crawlspace vents
  • power vents on timers
  • sometimes, homeowners just open and close their vents manually

All of these potential protocols have appeared on the market over the last 20 years. Each having its own set of disadvantages and pitfalls that homeowners should be aware of. Most importantly, the cost and accuracy of the systems. Encapsulations are expensive. Humidistat control fans and dehumidifiers are inaccurate and don’t operate efficiently in cooler temperatures as they are unable to calculate dew point. Barometric, and temperature controlled fans do not open and close at the right times. In fact, they can open up at the wrong times often inviting unwanted air into the crawl space environment. Dehumidifiers use a lot of energy and have to be replaced quite often. Closed crawlspaces destroy air quality, allowing the off gassing of soil gas, and other construction materials to percolate up into the living areas. Homeowners often complain about cat urine smells after the crawl space has been encapsulated. Forced air induction pressurizes the space pushing unwanted air into the upper areas of the home. Heating the crawlspace does not reduce moisture. Cooling the crawlspace can waste energy, as it is the only way to pull the moisture out of the crawlspace environment. Often, a supplemental dehumidifier is still needed to assist a crawl space set up on forced air. These are just a few of the setbacks reported.

The good news is there is a way properly engineer your crawlspace vents to work more efficiently as the builder intended. The only fan technology on the market today that can solve this challenge is the Atmox Controlled Ventilation System. This dew point controlled fan system has a series of sensors combined with wood moisture sensor technology that can regulate the flow of air into the crawlspace in a controlled way. The exterior and interior sensors constantly send data to the controller, and the controller determines when the fans fire. All done with low-voltage technology. Once installed, the homeowner can enjoy a guarantee for moisture reduction as well as maintaining high air quality for the whole house envelope. It is important to remember that half the air you breathe each day originates from the crawlspace. Having an abundance of fresh air is certainly a plus. Often, there is no need for an expensive dehumidifier to achieve the desired results. For more information on this unique, science driven technology please feel free to reach out to us for more information. A site consultation at your home can be arranged to engineer the system to be suitable to your footprint.

Again, be careful of being pressured into purchasing things that you don’t need by franchisees, or commission based sales people. Always do plenty of research, and remember, “Don’t Encapsulate, Ventilate!

Have a great summer!


Michael P. Masserang

Crawl Space Air Quality Specialist

Masserang Consulting





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