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Radon Mitigation
Radon mitigation systems are typically Passive or Active
Passive Systems
Radon levels can often be lowered simply by increasing the amount of fresh air flowing through an area such as a crawl space. Also see “Radon Resistant” construction below.
Note: Pipes in crawl spaces, if not insulated, can freeze during cold weather.
If a crawl space is not insulated, adjacent living areas will require more heating.
Active Systems
• Sub-Slab Depressurization
This is where negative pressure is created under a concrete floor by means of an electric exhaust fan system that keeps radon from entering a building and vents it to above the roofline.
• Sub-Film Depressurization
Exposed soil in a crawl space is covered by multi-ply, cross-laminated plastic sheeting, and all edges and seams are sealed. Radon is then vented to above the roofline by way of a fan-driven exhaust system.
• Crawl space Depressurization
An exhaust fan is used to pull air out of a crawl space; this lowers air pressure in the crawl space and pulls radon away from adjacent living area. Depressurizing a crawl area is often combined with reducing the number of perimeter vents.
• “Radon-Resistant” / New Construction
Passive Systems
Perforated piping is buried under a new buildings structure. Using rising heat within the building (“stack effective”) radon is drawn up through vent piping within the building to above the roofline.
Active Systems
If the stack-effect in a building turns out not to be sufficient to lower radon levels passively, exhaust fans are attached to the vent piping to enhance draw.
• In Water
Radon is a gas and, like oxygen, can be absorbed into water.
Elevated levels in water are typically associated with well water, not domestic water supplies.
Radon can be released (out-gassing) from water from showers, laundry washing, etc.
It takes 10,000 pCi/L of radon in water to out-gas into 1 pCi/L of radon in the air.
Mitigation from water is usually by way of an aeration system attached to the incoming water supply line to a building.
• Heat Exchange Systems (radon reduction by dilution)
This type of system takes heated, stale indoor air is vented to the outside, and fresh outdoor air is brought in. Before reaching the outside, the heat from the old indoor air is captured by a radiator-like assembly and transferred to the cooler incoming fresh air.
The end result is dilution, to some degree, of the amount of radon in a building; thus,
Heat Exchange Systems
• Do not keep radon from entering a building.
• Typically costs more than other mitigation techniques.
• Air Filters
Air filters, by themselves; usually do not do a good job of removing radon. A good discussion on this topic can be found at:
http://www.fantech.net/eletronicaircleanersvshepa.pdf
• Sealing Radon Out
Sealing concrete walls and floors is not considered an effective, long-term solution. Why?
• It is virtually impossible to seal 100% of any area and, since radon is a gas, it can get through the smallest cracks and gaps that may have been missed in the sealing process.
• New concrete shrinks and expands over time, so some cracking will eventually occur, letting radon in.
• Most soils under buildings is “expansive”, meaning it expands and contracts with how much moisture is in it – expanding during the wet season, and contracting during drier weather.
• All this leads to further cracking that can compromise any sealing that has been done.
• Post-Mitigation Testing
The only way to know a mitigation system is effective is to test.
You should always do a short-term radon test immediately after a mitigation system has been installed.
It is also recommended that you do periodic testing every year or two to check on system performance.
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