I’d like to thank Professor Kaste and Mr. Swenson for researching and writing about radon gas (Virginia Gazette, May 14, 2022). Please continue this important work.

I’d like to add some insight for everyone to consider in such an endeavor: water vapor coming out of the ground into homes.

If water vapor is seeping into a home, so would radon gas when it’s present in the soil below. Most homes built locally have what are called crawl spaces between the top of the soil and the inside of the home. This is a matter of architectural style and economy of construction. The style of the Colonial Williamsburg Restored Area may read like crawl space construction, but today most of those buildings have basements, not crawl spaces.

Part of my career as an architect included forensic work on existing buildings. To summarize part of what I’ve learned doing building forensics is that water vapor is a huge health problem locally. Crawl spaces serve a purpose visually and get the bottom floor off the ground, but a crawl space conveys water vapor into a building very easily. Ventilating a crawl space can make matters worse because if outside air is circulated through a crawl space the only thing you’ll do is introduce even more moist air and that moisture will cause mold to grow inside a building.

Historically, buildings did not have air conditioning systems. The introduction of A/C systems into buildings has exacerbated the moisture issue where water vapor comes in contact with cooler surfaces. I once saw a crawl space house in one of our high-price neighborhoods that had standing water sitting on top of some of our finest pottery clay soils, which prevented standing water from seeping down into the ground. And, since the lot was dead level and the crawl space was a couple of inches below the top of soil outside the home, water pooled in the crawl space. The interior of the home was visibly green from the mold that had accumulated on everything in the home.

The corrective work I prescribed was a double layer of heavy polyethylene to cover the ground with the edges of the plastic turned up the wall and duct tape on all the edges and seams of the vapor barrier. Then a couple of dehumidifiers were installed permanently and the water that was extracted from the air of the crawl space was removed to the home’s exterior with hose. The mold was cleaned out of the interior and the home became habitable.

The best solution would have been to tear down the home and start over by providing proper site drainage of surface water, raise the crawl space’s lowest points a few inches above outside grade level. Cover the crawl space with a couple layers of 6 mil poly with lapped and taped joints and then pour four inches of concrete over the poly to encase the vapor barrier to best protect its ability to prevent moisture migration into the interior of a home. And be sure to block the vents to prevent moisture coming in from the humid air outside. Sounds like a basement. Also sounds like not using a crawl space at all. I think you’ll find that the same construction design will help prevent radon poisoning.

There are no absolutes in building construction, just moderation of issues to acceptable levels. Also keep in mind that building codes are not perfect, they evolve.

Zan L. Cartwright is a Virginia licensed architect. He can be reached at zlc@cox.net.