Answer to Question #11399 Submitted to "Ask the Experts"

If a home is built using native rocks from the ground or creek, will this increase the background radiation exposure? Should this practice be avoided if possible? Are there safer building materials and, if so, which has the least radiation?

These are interesting questions, and ones that really don't have easy answers. For example, I was in a city called Ramsar, Iran, in the year 2000. Ramsar has the highest levels of natural radiation of any inhabited place in the world due to surprisingly high levels of radioactivity in the local rocks and soils. One house I visited was made of the local rock, and radiation levels inside were so high that if these levels were at, say, a nuclear power plant, the public wouldn't be allowed to enter it. Incidentally, the family living in the Ramsar house was perfectly healthy—but I'll get into that shortly.

There's another case I know of from Sweden. During World War II, Sweden extracted oil from some black-oil shale and used the residue to make cinder block that was then used to make homes for the poor. It turned out that the shale was high in radioactivity and the homes had high radon concentrations.

So you can see that some building materials are quite radioactive and some aren't; those that are radioactive can have higher or lower levels of radioactivity. It all depends on the material. Okay, that's a little bit nebulous, so let me get more specific.

Wood probably is the least radioactive, followed by brick and concrete. When you get to geologic materials (rock or stone), it gets a little more complicated. With igneous rocks (granite, for example), the lighter-colored rocks are more radioactive. So red, pink, white, and light gray granites tend to be more radioactive than are black "granites" (which aren't really what a geologist would call a granite—black granite is an architectural term). So a house that's made from granite, whether it's sheets of granite or granite rocks, is more likely to have elevated levels of radioactivity than would a frame house.

Some geologic materials have fairly low levels of radioactivity. Sandstone is one: most sand grains are quartz (some may be feldspar), which is usually pretty low in radioactivity. Limestone (marble too) is usually low in radioactivity, although the local rock in Ramsar is freshwater limestone that happens to have sky-high levels of radioactivity. Having said that, Ramsar is an unusual place; as far as I know there's no other place where the limestone has this property.

Okay, so let's put all of this together.

First, there are some extreme examples—like the freshwater limestone in Ramsar or the black shales in Sweden—in which rocks can be radioactive enough to potentially give you a high dose of radiation. And in these locations, studies have been done and there's no indication that living in these dwellings is harmful.

Second, there are some geologic materials (real granites, for example) that have more radioactivity than other types of rock. But—and this is important—even granites don't give you a high enough radiation dose to be dangerous. I live in New York City, where we have a lot of granite buildings. I can measure the radiation from these buildings and there's no doubt that it's somewhat elevated, but the dose rates are still far too low to be a health risk.

One final thing: even wood, brick, and concrete give off low levels of radiation—usually not much, but some. You won't be able to find any building materials that are totally bereft of radioactivity; it's just that some are more radioactive than others. But unless your house is made of something with exceptionally high levels of radioactivity, you don't have to worry that it will affect your health.

P. Andrew Karam, CHP