[GSBN] Still ventilating

Tue Apr 9 13:32:33 UTC 2013

Thanks for your comments, John.  I'm hoping you will say a bit more about the best practices, and how they work.  I've been reading radon remediation recommendations for years, and have questioned some EPA and environmental safety officials, but I still have doubts about a few elements of their recommendations.

I understand the value of building a very airtight enclosure where it contacts the soil, perhaps including a membrane that will impede the upward migration of radon.  I see the value of the sub-slab gravel bed connected to a vent stack, in making sure that the air pressure in the soil below the building is not higher than the ambient atmospheric pressure, since higher pressure would help drive the radon into the building.

However, I have trouble believing that the vent stack is actually removing much radon from the sub-slab space.  Radon has about eight times the density of air, so it won't naturally seek the top of the stack.  In a more open system, gases would mix enough to promote some escape of radon, but I doubt that there is sufficient mixing within the horizontal stratum of the sub-slab gravel bed to get a lot of radon to go up the vent pipe, whose square area is a tiny fraction of the slab area.  Much less if the slab is directly on compacted soil.

So is relieving the potential pressure increase below the building floor sufficient?  Apparently, testing says that it is, in many cases.  But I'm thinking that there would be value in establishing a small amount of air flow beneath the slab, so that some of the radon can be evacuated from below the slab.  This means an air inlet and to pair with the stack's outlet, providing a small but continuous airflow.  You mention a drainage mat on vertical elements, which may provide this inlet path.  Or maybe not, depending on how it is coupled to the sub-slab gravel.  The EPA doesn't include the drainage mat on vertical surfaces in their recommendations, at least as far as I can determine.  I just spent half an hour reviewing the EPA Radon web pages.

The EPA plan for adding a fan to the design always reminded me of putting your mouth over the top of an upright Coke bottle, and trying to suck the last few drops off the bottom.  (I admit that doing this used to amuse me, as a child.  And yes, it is completely ineffective.)  Depressurizing the under-slab area would certainly help prevent gas migration into the house, but without airflow, not a lot of radon would move out the stack.

In cases where radon levels are very high, and especially if they aren't reduced sufficiently by the vent stack with fan, do you think providing inlet air vents to the sub-slab gravel bed would be useful?  It wouldn't be horribly difficult to retrofit these vents in houses that show persistent problems.  In fact, evacuating soil gases from below the slab seems like a reasonable idea in some other cases.  In my area, we have a serious problem with natural gas under the slab, caused by corroded buried gas lines in homes built in the forties and fifties.  The local gas company says that when the gas pipes leak, the soil methane levels create a significant explosion risk.  They say they have some method for sucking out sufficient gases to reduce the risk, but I haven't been able to get a detailed description of the process.  Is there any reason to try to evacuate sub-slab soil gases, just as a preventative measure?

If there is radon present in the domestic water supply, what impact does that have on the home's ventilation requirements?

Looking the other side of the risk equation, the EPA quotes CDC, National Center for Injury Prevention and Control, and National Safety Council figures, that radon kills 21,000 people each year, in the USA (2006 figures), 7.5 times as many people as home fires kill each year.  http://www.epa.gov/radon/pubs/rducrsks.html  This is due primarily to increased lung cancer.  I've seen some people dispute the validity of the radon/lung cancer estimates.  Do you think the estimates are valid?

Thanks again, John, for your information and viewpoints, and thanks to Feile for providing greater detail on her experiences, and the situations in Ireland.

Best wishes,
Derek

On Apr 8, 2013, at 1:35 PM, John Straube wrote:

Hi there,
Use best practise Radon control: a very airtight enclosure that interfaces with the soil, an air permeable gravel bed / drainage mat around the horizontal and vertical elements respectively, and then connect this layer to a passive stack pipe that runs vertically with no elbows through the living space and projects about the roof ridge and above snow pile depth.
If the radon levels remain high in your spot checks, add a radon fan.

Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sustainablesources.com/pipermail/gsbn/attachments/20130409/3fc55417/attachment.htm>