1- Introduction:
Exposure to Radon gas in our homes is the second leading cause of lung cancer after smoking, with 16% of lung cancer death directly linked to Radon.
This gas is the main cause of lung cancer for non-smokers.
However surveys tell us that only 1% of North Americans are aware of this danger.
2- Definition:
Radon is a tasteless, odorless and invisible radioactive gas produced by the natural breakdown of radioactive metals such as Thorium, Uranium and Radium which are unevenly found in rocks such as phosphate, granite and shale as well as in soils all over the planet crust.
Radon is readily present in low concentration in the earth atmosphere at about 0.3 pico curie per liter (pCi/L) of air on average.
A pico curie is a unit measuring radioactive contamination.
Although it dissipates in open space, Radon levels tend to steadily increase in non ventilated enclosed areas.
The daily amount of Radon gas that naturally escapes from the ground at a specific location is dependent on the type and concentration of metals in the soil at that site.
Radon leaks in our homes through cracks in the foundation and concrete slab in basement, crawl space and gaps around pipes.
In winter when windows are closed, these radon gas leaks can accumulate to radiation levels comparable to receiving thousands of chest x rays.
About one out of every fifteen North American buildings contains dangerous levels of Radon.
3- Detection and testing:
Predicting a site will have a radon problem from region history is not possible as gas levels can be highly localized.
Radon levels can greatly vary from one house to the next neighbor’s house.
A- Radon land test is done on a vacant lot before the house is built to indicate whether or not a radon problem may be
present at the proposed building site.
This test will not predict what Radon levels will be in the finished home but rather could help us decide if Radon mitigation measures should be included in the house design and installed during house construction.
This land test uses a box with open side placed directly over the soil to collect gas released from the ground for a predetermined amount of time.
A carbon medium inside the box traps the gas to be latter measured in a lab.
This soil test may be too localized to actually tell us anything about the Radon situation and thus quite useless.
At the time a house is built on the site, then it is possible to test for Radon.
Best is to plan for Radon mitigation from house design stage and build it right from the start by including an inexpensive Radon passive system or an active one if need be.
B- Radon indoor test kits are inexpensive and easy to use.
Test kits may cost from $15 to $40 with Lab analysis another $15. Those kits are available at home hardware stores and government lung association offices.
A short term test of 2 to 7 days is most common.
However a longer 3 month winter test will give a more precise average Radon concentration for the year.
Kit should be placed in lower level living spaces where Radon is most likely accumulating.
If testing shows more than 4 pico curies per liter of air then EPA recommends mitigation measures must be taken to lower Radon toxicity.
As more studies have been completed about Radon health impact, health agencies around the world are recently advising Radon indoor target levels below 2 pCi/L.
4- Infiltration
A- Gases move from high pressure to lower pressure areas.
Building inside air pressure is usually lower than in the soil below the house, because of the stacking effect of a building on the ground below, kitchen / bathroom fans…
Radon will infiltrate a house through cracks in concrete slab and foundation walls, gaps around service pipes and bearing posts.
B- High concentration of Radon may be present in ground water and springs.
City water is most likely treated to eliminate Radon toxicity.
However well water can carry high concentration of Radon.
Radon is best released from water when pressure is lowered, temperature is raised and water is aerated. Thus shower heads can release significant amount of that gas in a bathroom.
C- Indoor stone work like granite counter tops, bed headboards, fireplace veneers and floorings may contain radioactive metals that will release Radon at sometimes high levels.
To be safe, inside stone work should be tested for Radon before installation.
5- How to reduce in house Radon toxicity level?
A- Sealing a crawl space with a plastic barrier and caulking will not stop soil gases from entering the house as long as air pressure differential still exist from soil to living space above.
B- Diluting radon by increasing air ventilation in a basement or crawl space is not a viable solution as it actually draws Radon in from the soil and can dramatically increase home heating and cooling costs, even if a heat exchanger is installed to recover energy.
C- Stopping Radon from infiltrating the living space by depressurizing the sub slab soil is the best Radon mitigation system.
6- Radon mitigation systems
It does not take much of a crack in basement concrete slab for gas to seep from soil into living space.
As long as air pressure is higher in the soil below living space, soil gas will likely find a way in.
By sealing the living space from soil below and also depressurizing the soil passively or actively, then Radon will not enter the home.
For the new home construction, before pouring concrete slab in basement or slab on grade, lay down 6” of gravel (1/4” or bigger) to allow the Radon to freely move to a perforated drain pipe embedded in the gravel layer.
Lay several runs of pipe if inside foundation area is large.
Cover the gravel with 6 mil poly vapor barrier that also acts as a gas retarder. Overlap poly by 12” at seams.
Use a T fitting to connect drain pipes to a 3” diameter PVC vent pipe that will travel up inside partition walls to roof with minimum or no horizontal runs.
Pour 4” concrete slab for basement floor or slab on grade at main floor.
For crawl space, also pour up to 2” of concrete skim coat over poly to ensure rodents do not pierce poly and render gas sealing barrier useless.
Urethane caulk all expansion joints and cracks to seal the floor.
A passive Radon mitigation system means the exhaust pipe will pierce the roof and naturally vent the sub slab soil to atmosphere above the roof.
To activate a Radon mitigation system add a fan to the pipe in attic or just under roof in partition wall to force exhaust soil gases and create a reverse air pressure between soil and living space that will stop all gases from entering the house.
Add a Varmint guard at top of vent pipe (above roof) to keep animals and debris away from fan.
A passive system is likely all you need to lower Radon contamination to acceptable level.
However an active system fan may need to be turned on for more extreme Radon levels.
Monitor the Radon level with follow up tests to ensure mitigation system is working properly. Existing homes with a Radon problem may require the attention of a professional to figure out least expensive but most efficient mitigation system for that particular home.
7- Last Word…
Radon gas deadly health effects in our homes was unknown to the public until after the 1984 Stanley Watras incident.
Watras, an engineer at a nuclear power plant set off radiation monitor alarms at work.
After an investigation, it was discovered that the radioactivity was not coming from his work place but instead from his home which registered 700 times more radioactivity than safe to humans.
Radon mitigation design is required for new homes by an ever growing number of building departments.
Testing for Radon when buying a home or designing a mitigation system for your new home should now be part of the must list.
Be safe…
