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Stack Effect & New Jersey Crawlspaces

You probably noticed when you read my Owner’s Message that, while discussing the latest building science developments affecting our approach to improving your crawl space environment and your overall home air quality, I mentioned something called the “Stack Effect”. Well this scientific phenomenon is the very reason why building science experts, engineers and international building codes, for more than seven years, have recognized that to simply vent crawl spaces to the outdoors, which was the earlier approach, has the potential effect of creating hazardous moisture build-up in crawl spaces which in turn promotes the unhealthy conditions that can lead to mold growth, wood destroying fungi, wood decay, foul odors and termites and other wood destroying insects.

The old thinking regarding venting was to place crawl spaces vents opposite one another with the idea being that outside air would enter one side of the crawl spaces and exit out the vent on the other side. It was thought then that in this way you would remove damp, musty crawl space air with clean, fresh outside air. Actual building science, however, now convinces us that this simple theory, in reality, does not work. The reason it doesn’t work is due to the Stack Effect.

You see as air enters the lower level of a home its initial response to the indoor environment is to move upwards in the house, like air in a chimney. The upward movement of air is called the Stack Effect and it is caused by wide pressure and temperature differentials or the difference in air density between the exterior and the interior of a building. This cause and effect is now recognized as the natural movement of air in a home or building. Warm air is lighter than cold air. Thus, in the summer, as warm air enters a crawl space through a crawl space vent it rises in the home to the upper levels and eventually escapes out through open windows or other points of leakage. As rising warmer air reduces the pressure in the lowest level of the house, more outdoor air is forced to infiltrate or be sucked inside through the vents, poorly sealed crawl doors or other points of leakage.

Since no home or building is a complete vacuum, when air rises it must be replaced with new air coming into the home or building. Thus a continuous pattern of air flow is created. The Stack Effect functions in both the summer and the winter. You might think of it like sucking liquid through a straw. You house sucks air into the house and up from the ground. If that air is wet, humid or moisture laden, like in the summer or on other rainy, high humid days, passive crawl space vents will actually increase the moisture and humidity levels in a crawl space. Thus, the vents that were originally thought to remove moisture, in reality, are the cause of many crawl space problems and unhealthy relative humidity levels in your home. High relative humidity levels can promote mold and mildew growth, dust mites, lead to wood decay and structural wood rut and infestation of wood destroying insects, such as termites. A crawl space left in this state will become musty, moldy, and foul smelling with that foul odor, mold spores and dust mites eventually being drawn by the natural air flow up into the upper, living areas of the home. Experts agree that, on average, 50% of the air you breathe in your home originates in your crawl space or basement. Shouldn’t that air be as fresh and clean as might be possible?

In addition, traditional crawl space venting also increases energy loss and creates higher heating costs in winter months due to having colder outside air sucked in and then rising as a result of the home’s natural suction forces at work, caused by the Stack Effect.

“SHORESPACE” is Jersey Shore Home Moisture Management’s latest combination of Intelligent Crawl Space Systems designed to properly control moisture in your crawl space, rid your crawl space of unhealthy mold spores, mildew and dust mites, prevent future mold growth and wood decay, save you energy and lower your energy bills.

Don’t jeopardize your family’s health and the value of your home by neglecting the environment in your crawl space. Obtain the immediate benefits of a Comprehensive Crawl Space Evaluation and learn which combination of “SHORESPACE” systems is right for you and your home.