WPB Enterprises Inc.
Oldest & Most Experienced
We guarantee Radon levels below 4.0 pCi/l
Can Building Materials Elevate Radon Levels?
Granite Counter Tops - Granite Tiles - Concrete
There has been concern about the possibility of granite counter tops or granite tile raising the radon levels or emitting Gamma radiation. The concern is Radon emitted from the decay of Radium in the granite can easily escape from unsealed surfaces of the granite into the air or that Gamma emissions from any radioactive elements in the stone may be excessively high.
Studies have found that very few granites contain enough radium (the parent of radon) and or other radioactive elements to be any concern. There are however many granites that have measurable gamma radiation and some that will emit significant radon. In general gamma exposure is consider a very slight risk. Many common materials such as miracle grow or other fertilizers emit elevated gamma levels.
The radon association AARST has recommended that if you are concerned about granite installed in your home you should purchase three radon in air test kits and place them in the following locations: one in the lowest livable area (basement), one in the main living area (bedroom or living room) and one in the kitchen, 20 inches or more from the granite. If the any test kits are at or above the EPA guideline of 4.0 pCi/l consult a radon professional listed with your state radon program.
Some surface coatings that are applied to the un-polished or polished side during the manufacturing can reduce the radon emanation rate significantly from that side but may not reduce the total radon emanation from the granite. The effect of sealing all sides is unknown. The surface sealants applied after the granite is cut to size by the installation companies typically has a breathable characteristics that may not restrict radon movement.
If you would like to try and test your granite countertop please read all of this page and then go to our Testing Information page to purchase a granite counter top test.
There is also typically some radium in concrete. In almost all cases this does not contribute significantly to the indoor radon levels. There have been a number of cases where the radon in the concrete did cause the rooms adjacent to the concrete to be above the EPA action level of 4.0 pCi/L. In the buildings where this happened there was typically a concrete ceiling as well as a concrete slab and the air change rate (ventilation rate) was extremely low.
Newer multi-story condo buildings that are constructed with concrete slabs and ceilings often have only one exterior wall that allows natural infiltration ventilation of the unit. If there is no mechanical outdoor air ventilation incorporated into the HVAC system, the air change rate in the dwelling may be so low that the small amount of radon coming from the concrete will cause the indoor radon levels to climb above the EPA action level. This will be even more likely to take place when there is moderate temperatures outside and the windows are not opened. During moderate temperatures there is no temperature difference driven airflow into or out of these units.
Bill's paper on Elevated Radon in High Rise Building from Concrete
What is Required to have a building Material Elevate Radon Levels
There are three factors that influence whether granite or Concrete can raise the radon levels in a room or an entire home.
Average Emanation Rate is Significant Quantity of the Material is large enough Ventilation Rate of the Room the Material Occupies is Low
The emanation rate of radon from granite can only be determined by making an actual measurement of the surface emanation. There are several methods of making this measurement.
Bill's paper on Measuring Emanation from Granite & Concrete reviews these methods.
Although placing a radon detector under a container that is sealed to the surface may produce an elevated radon level it will not measure the emanation rate unless the method has been previously calibrated and all the factors that influence the results carefully compensated for. An even more critical component is the fact that the emanation rate across the surface can vary significant and the surface coatings may be causing more or less emanation from one surface than another. Therefore a flux measurement of one area of a granite surface is unlikely to be the average of the entire granite piece.
Extrapolating the measurement from a single location of only one surface of the granite is likely to lead to large errors. Multiple measurements of the flux from both sides of the granite is necessary to determine if the emanation rate is uniform or if it varies significantly.
The next important variable is the quantity of granite that is installed, A kitchen may have 40 square feet of granite while another home may have 400 square feet of tile. The tile may have ten times less emanation than a countertop that is suspended on cabinets but in this case it has ten times more emanation surface area.
The final consideration is the ventilation rate of the area the granite is located in. Ventilation determines if radon emanation from a source will measurably elevated the radon levels, There are two types of ventilation happening inside a home, internal air circulation and inside to outside air exchange. The air change rate is typically measured in units of Air Change per Hour (ACH).
1.0 ACH is considered very high ventilation rate and 0.1 is considered a very low air change ventilation rate. The other ventilation factor, internal air circulation is very difficult to measure unless an air handler is uniformly mixing the air inside the home. Obviously a bathroom room with no mechanical air circulation or exhaust vent operation will have a very low internal air change rate when the door is closed.
During this time a bathroom with a lot of granite tile that emanates radon would reach its highest level after a few cycles of the ventilation rate. The lower the ventilation rate the longer it takes to reach the maximum radon level. 0.1 ACH requires10 hours for the air exchange to equal the quantity of air in the room. After 3 or 4 of these exchanges or about 30 to 40 hours the original air has most likely been replaced. The radon in this bathroom is therefore accumulating in the volume of the bathroom but once the bathroom door is opened it is accumulating in a much larger space that likely has a much higher ACH rate.
The point is that radon level increases will be greatly effected by the ACH rate, the internal air circulation and the size of the room the air change is taking place in. The radon level is directly related to the ACH rate and the volume of space this ACH is happening in, not how long it takes to get to the maximum radon level. A kitchen is typically open to the main living areas of the home and this area is often connected to an internal circulation system which makes the entire house the volume when the air handler is operating.
A few calculated examples will illustrate the results. A 10' by 15' bathroom with an 0.1 ACH rate and 200 ft2 of granite tile that emanates at a rate of 10 pCi/ft2/hr will have 2000 pCi per hour moving into an air exchange rate of 10 X 15 X 8 X 28 X 0.1 or 3360 liters per hour. The 2000 pCi/hr will be diluted by the 3360 liters to cause the radon levels to rise 0.6 pCi/l. If the ventilation was half this amount the radon levels would be 2x higher.
To see some pictures of what a radon system looks like go to the WPB Job Photos page.