The crawl space is part of the load bearing framework of a house. For this reason, care needs to be taken in the design, maintenance and reconfiguration of these spaces. The modern crawl space should be a dry, energy efficient, and functional area that provides structural support and easy access to critical electric, plumbing and utility functions. Having a crawl space that performs like a mini-basement is considered the highest and best use of a crawl space.
The Moisture Problem
The crawl space can be a wet, musty breeding ground for mold. Left unchecked, mold will migrate into the living space of a home and create a health hazard. For most of the last century, building codes and conventional wisdom have called for the ventilation of crawl spaces as the primary means of moisture control. Today, construction engineers are rethinking the wisdom of this solution as the science indicates that outside air is actually making moisture problems worse. Except in very limited circumstances, existing building codes do not permit the construction of unvented crawl spaces in many parts of the country. These limited circumstances do include “conditioned” crawl spaces that seem to perform better than vented substructures.
Apart from temporary storage, a home’s crawl space will not often be put into service. Nevertheless, there are homeowners who opt to cover interior crawl space walls with insulation and drywall. Some homeowners will actually pump poured concrete into their crawl spaces in order to create something comparable to a basement floor. This is not always a good idea because the water content of standard concrete could compromise the home’s air quality by introducing mold-producing humidity and silica dust. One alternative to pumping concrete into a crawl space is a liner sealing system that makes the crawl space air-tight.
Microbial Contamination of Indoor Air
According to the Wiley Online Library, an international publishing clearinghouse of scholarly works, microbial contamination of indoor air can occur when outdoor air is transported into the crawl space through vents raising the relative humidity of it. Humid conditions create the conditions conducive to mold and mildew. When air entering a home does not have appropriate routes to take, it will find its way in through leakages. Owing to normal ventilation, living spaces inside a home are subject to lower air pressure than crawl space air. For this reason, pressure differentials can draw potentially contaminated air from the crawl space into the living space of a home.
Vapor Barriers Stop Moisture and Pests
The sandy or earthen floor of the average crawl space should be covered with a polyethylene vapor barrier (plastic sheet). One timely LA Times newspaper article disclosed that the use of a vapor barrier will reduce the amount of moisture entering a crawl space through the natural process of ground water evaporation. This is beneficial because keeping that area dry will reduce the potential for wood rot and mold. Moreover, arid conditions in the crawl space also cut down on wood-destroying insect activity.