Arkansas HVACR NewsMagazine September 2020

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COMBINATION PIER AND BEAM/SLAB

insulations. Topsoil may be shallow, with rock ledges or shelfs that trap moisture just below grade or direct rainwater in unexpected directions. Clays can hold tremendous amounts of moisture for long periods beneath structures. When we build tightly for efficiency, we effectively place an airtight container over the ground. A site evaluation and plan should be in place to address sprinkler systems, roof runoff, and groundwater. The plan will outline the use of retaining walls and routing of surface water by alternative methods during weather events. In those crawl spaces, we must employ use of a vapor barrier and ballast. The barrier, securely sealed to the framing, keeps moisture out, and the ballast provides weighted stability for the barrier. Without the ballast, seasonal moisture can displace the barrier and compromise effectiveness of the system. While the HVAC contractor is not responsible for this scope of construction, understanding the basic principles (and what to avoid) will keep contractors from wasting their time and the customer’s money on remedies that treat symptoms and not the problem. In a ventilated structure, for example, crawl space management may solve the problem. In high-value insulated homes, the solution may include mechanical humidity management. MANUAL LLH (1,500 SQUARE FEET PER TON OR MORE) As a guide to providing solutions for well insulated homes, ACCA has

When pier and beam and slab configurations are combined (see figure 6), all crawl space must be sealed against air and moisture as outlined in the previous paragraph. Any ground moisture in the crawl space will begin destructive work on the structure. Moisture will make its way into the structure through the framing, subflooring and flooring while internal latent loads will climb to an unmanageable degree.

As we slow the rate of air change in any structure, we can anticipate a rise in humidity or latent loads due to internal gains from cooking, washing clothes, washing dishes, taking showers, and even breathing. Any time high-value insulation and air sealing components are used where humidity solutions are not provided or limited, the result can be biological growth in and on construction components, ducts, and equipment. Some of this biological growth can set up allergic reactions for occupants or attack the integrity of construction materials. Even in warm climates, there is ample moisture in the ground to cause problems when building with high-value