How to reduce radon level in my house?
seiyafan
| Posted in General Questions on
When I first bought my house a couple of years ago the radon test was conducted in the first floor (bi-level house on concrete slab, all above grade) showed 3.5. A couple of years have now passed and I have since replaced all the windows and sealed all the gaps I could possibly find. Last week I did the same test again (using the same setup as my home inspector) and it was 12.1, ouch! Does it mean I made the first level too tight? What are my options to fix it?
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I am in Lemhi County Idaho. We have some of the highest radon levels in the country. The best way for new construction is to put two layers of thick plastic sheeting down, protected by about an inch of sand under all of the concrete to seal the slab against the penetration.
As a retrofit, you need to intercept the radon before it can enter the building by constructing a vacuum venting system, consisting of penetrations through the slab, and venting pipes hooked to a dedicated fan, to pull the radon out of the soil and vent it outside the house.
The EPA has some good basic documents on how to construct a system, and what all the components are, (I'm attaching one of them). Many states where radon is an issue also have guidance documents.
The systems are typically pretty simple to install, but you want an experienced contractor. I've had to correct several installations, where the installer failed to properly seal the vent piping to the slab. On one, the use of two tubes of urethane sealant, increased the suction from 1/2-inch of water, to 4-inches, and dropped the radon levels from 12 to 2.5 pico Curies/liter.
Good luck, Randy.
Joe,
You might want to do some more testing -- perhaps with a different type of test kit -- to confirm your radon levels.
If further testing confirms that your radon levels are high, you may need to install a radon mitigation system. Here is a link to an article that discusses radon mitigation:
All About Radon.
Another test was done and high radon level is confirmed, I think I will install a radon fan by drilling a hole in the slab (and hope I will find gravel), but I have a question on the hole location. Here's a rough sketch of the first level (http://s15.postimg.org/wfdldjtrv/Capture.png), one possible location is inside the closet in the bedroom, another is in the garage. My preferred location is in the garage but will it be equally effective as compared to the closet? In other words, If a fan is designed for 1500 sq ft, does it make any difference when placed at a corner or in the center? To save on electricity I don't like the idea of using an oversized fan.
It's hard to predict which will be most effective, but toward the center seems like a better bet--less distance it has to "reach". So I vote for the garage. There are lots of variables you can't know--how much gravel and how clean it is, soil types underneath, locations of cracks it comes through to the house.
Electronic monitors can give you an ongoing reading for both reassurance and quick feedback on what is working or not. If you get one, it's worth checking with another test type to verify after you think you have it all set.
Joe: My new house is pretty tight, .59ach50. The typical radon piping under the slab was installed. W e placed heavy poly on top of the foam and under the concrete slab, carefully sealing the penetrations.
Last week I finally got around to radon testing. I was dismayed to see readings varying from 13-18. While I am waiting for the radon abatement system to get hooked up, I increased the HRV fan from low speed to medium. The drop in radon level was dramatic. It's still fluctuating, but is between 4 and 8, occasionally as low as 2.
My take is that ventilation can be an important part of radon control.
Kinda sad how once you spend a lot of time and money on airtightness, then you need to spend a lot of time and money on installing and running always-on mechanical ventilation and radon mitigation systems to protect your health in your fancy "green" house. In the quest to cut down on heating bills, we make ourselves dependent on these new mechanical systems that increase our electric and maintenance bills! And what happens when the power goes out for a few days? Open your windows in the dead of winter and wish you had that wood stove that your airtightness goals precluded? What if one of these systems silently breaks? It could be years before someone notices, especially for a radon mitigation system, and all that time people are increasing their risks of lung cancer.
It all just seems so inelegant, like a problem solved in the crudest possible way by throwing complication at it.
Nate,
A lot of these houses sure seem to make a mockery of any claims to be "passive". This appears to be the direction that the energy efficient community has decided to take. There are alternate paths, but as codes increasingly follow this more technological dependant approach, other ways of buildingmay become much harder to implement.
Malcolm,
I would be interested in hearing your thoughts about the 'alternate paths' you mention. I am not doubting that there are such paths. Rather, I would like to hear your (and others') opinions about what they might be.
In many cases the pressure/ flow characteristics of the sub- slab venting are very low flow at high pressure. But the widely used fans are a poor match to that. And they use low efficiency motors. With good fans chosen to match measured chacteeistics on each job, the energy consumption of the fan could be cut to perhaps 20 W rather than the 50+ watts used now.
One example I've come across is the following completely passive ventilation system that can replace complicated HRVs: http://www.ventive.co.uk
Still a product, still costs money, still requires a contractor to install, but it's an elegant product that's not some electromechanical gizmo that ads complication, can break or malfunction, and introduces a phantom load to your electricity bill. This seems like a much more satisfying solution to the problem of heat recovery ventilation than yet another bulky electricity-driven box full of fans, solenoids, and sensors.
I am going to dig out the dirt next to the slab wall to see exactly what's underneath.
Nate- I looked at the Ventive brochure, but still don't understand how it works. Supposedly, it recovers heat as air goes out the chimney, but then what? I'm no engineer, but I'm not convinced.
As far as I can tell, it's a pipe-within-a-pipe system. Inside and outside air flow in different directions, through the two pipes, exchanging heat through the wall of the inner pipe as they flow. No idea if it works as well as they claim but they advertise several case studies and working installations.
The Ventive system is intuitively appealing but it has some challenges. It runs on stack effect and/or wind. That means that you probably don't get enough ventilation on mild days, and you probably get too much on cold, windy days. The other problem is that if the heat exchanger works well, the temperature in the ducts will near the interior temperature, which will reduce the stack effect. So the stack effect would would be full force only for the portion of the stack that is above the heat exchanger, sticking up above the roof. You could make that 15 feet high and it might then give you as much airflow as a pair of Lunos ductless HRVs. Or you could buy a pair of Lunos, which consume 1.5 W each. Then upsize the PV array by 15 W to compensate.
OK, the Lunos solution is high tech. There are electronics in there. But the Ventive system is a lot more complex to install, and there's plenty that can go wrong with roof penetration or a tall stack sticking out above the roof.
Wow, I never knew there is ductless HRV, now that gets my attention!
eGO requires 12-inch wall, ouch!
And the price is outrageous.
There are cheaper clones that don't need such thick walls, such as http://www.homedepot.com/p/VENTS-US-TwinFresh-Comfo-32-CFM-Power-5-in-Single-Room-Energy-Recovery-Ventilator-Twinfresh-Comfo-RAI-50-2/204785337
Still expensive, but not as much as the Lunos products. And they'll get pricey if you're planning on installing a couple.
Bob,
I'm not advocating for any huge directional change, simply that when a building assembly or mechanical system is evaluated for suitability we do it on the basis that it doesn't add undue complication, reduce the resiliency of the dwelling, or disempower the occupants from modifying their own homes.
- Building assemblies shouldn't rely on absolutely maintaining the integrity of their air-sealing over the life of the structure for their longevity.
- They should be simple enough that the future owners, without expert knowledge, can modify them over time without compromising them.
- When choosing a mechanical system, or any engineered component of the house, it's worth taking a slight hit on efficiency to favour the simple over the complex. Especially if this reduces the extent to which the house relies on electronic controls.
Except for new construction, the houses I work on invariably have experienced some modification, and deterioration. Their occupants are not building science enthusiasts, and in many cases they are lived in by people with no interest or understanding of how even these simple structures work. That's who we should be designing for, not the regular posters here on GBA.
Does the TwinFresh Comfo 32 only recovers heat or cooling as well?
Cooling as well, but the moisture recovery is poor. ≤ 20%.
I just dug a hole right next to slab wall outside of the garage, and I gave up after going down 16 inches! Did I do something wrong? Is the slab going down further on the edges?
Joe,
If it is a slab on grade then the edges have probably been thickened to take the loads of the exterior walls. If it is a slab within stem walls then these may extend down as far as was necessary to either get below frost depth or to good bearing soils.
Yes, those are the footings--the house's foundation. The inner floor slab is not structural and is probably a maximum of 4" thick.
That makes sense.
Right now I am testing the radon level using the bathroom fan controlled by a timer (15 minutes on / 45 minutes off) to see if makes any significant difference. If yes I will get the TwinFresh. If not I will install a Radon fan.
Joe,
If new air will be the cure, I'd recommend the Lunos. We've had them two years now. We're getting by with one pair for our 1,200sq. ft. and that's pushing it a little. They're amazing for just 12V DC (you can throw away their cheap China made 120VAC/12VDC inverter, could be run with a tiny solar panel and battery if you want). When it was -20F outside, I measured 48F coming in when the opposing fan was running. They run opposite each other every 70 seconds and have 3 speed settings.
They do make them for US stupid (2x6) walls now as well.
PK
The Lunos or Twinfresh might help even if the bathroom fan does not--the exhaust-only ventilation might depressurize the house and suck more in through the cracks in the foundation, whereas the ductless HRVs would ventilate without depressurizing. To reduce depressurization during your tests exhaust fan tests, cracking a window would help.
BTW I previously recommended the center of slab location for the fan. I've lost confidence in that recommendation. There may be more leaks to the interior around the perimeter, and the soil at the perimeter may be less dense and allow more airflow. So a fan at the perimeter might have better "access" to depressurize the perimeter. Unfortunately, the only way to know for sure is to try it. There are tests one can do with test holes drilled in a few locations, but that only improves the quality of the guesswork--it doesn't prove what will work. But you are close enough to acceptable levels that I expect that either would work...if you need them at all once you have ventilation working.
I think I will go with a radon fan + bathroom exhaust at this time, the radon fan should more or less prevent the bathroom exhaust from sucking in more soil gas through the cracks. Later when budget allows I will add a ductless HRV.
There are three loading bearing poles along the center of the first level, 2 in the garage and 1 in the living room. Do you think there is sub-slab footing underneath? I am wondering if it's necessary to dig another suction point on the opposite side of the first.
Joe, I do not think that multiple suction points are an issue if they are all hooked together to vent through the same system. Someone can correct me if I am wrong.
Joe Blanco,
The three load bearing posts will very likely bear on concrete pads, not strip footings.
I sealed expansion joint of the slab in one section of the first floor, radon level went down from 10~15 to 3.8
If the radon fan is constantly remove air beneath the slab, the air removed must be replaced by the air outside, so won't the slab become colder during winter months and during summer months hotter air will increase chance of condensation?
I'd like to address two questions that have come up in this thread.
The first question concerns whether tight homes (homes with low rates of infiltration and exfiltration) are more likely or less likely to have radon problems. This issue has been investigated by researchers, and the conclusion is that there is no correlation between airtightness and radon levels. Leaky homes can have high radon levels or low radon levels. Tight homes can have high radon levels or low radon levels. Other factors matter more than the airtightness of the home's thermal envelope.
Here is a link to an article with more information: All About Radon.
The second question concerns whether an active radon mitigation system that includes sub-slab depressurization ends up cooling the slab. The answer is, it does not. I wrote an article on this topic that was published in the March 2007 issue of Energy Design Update. In that article, I wrote in part:
"Radon mitigation fans usually have airflows in the range of 100 cfm to 200 cfm. Although most radon mitigation contractors assume that the makeup air supplying the fan comes from the soil under and around a home’s foundation, little data exist on the source of makeup air for radon mitigation fans. “One of the key questions we’d like to investigate is, Where is the makeup air coming from?” says [researcher Brad] Turk.
"“Unfortunately it is difficult to track air from the soil, other than by using radon as a tracer gas. Our current hypothesis is that a lot of the makeup air is coming from upstairs, or from outside, entering around the rim joist.”...
"According to Turk, the percentage of soil air in radon fan makeup air varies with soil type. “It depends on a lot of factors, including how tight the basement foundation is and how tight the soil materials outside the foundation are in comparison to the basement materials,” Turk explains. “For example, in New York state or eastern Washington, the soil is often glacial till, which is a highly permeable material. You can move a lot of air through glacial till. In those areas, you may find that a significant part of the fan’s makeup air is coming through the soil. But there is a large range in how much of the air entering the basement is soil air. It can be as high as 20 or 30 percent — or in some cases, if there is tight basement construction and impermeable soil, it can be almost unmeasurable.” ...
"Nagan admits that the source of the fan’s makeup air is somewhat mysterious. “If in fact the makeup air is coming from the soil outside the foundation, why aren’t we chilling the crap out of these slabs?” asks Nagan. “I’ve measured the temperature of the slabs, are they’re warm.”
"According to Turk, soil air reaching the crushed stone under a slab usually has a temperature of about 50°F, so in most cases soil air does not significantly chill a basement slab. “Around buildings, there can be a few direct pathways that connect the outside air to the crushed stone under the slab — for example, the shrinkage gap next to the foundation where they backfill,” says Turk. “A subslab depressurization system can pull the air down next to the foundation wall, and in some cases you can see the air pulled down by using a smoke stick. But the path that the air follows is almost unknowable — there are so many permutations and pathways, so many materials that are not homogenous. You don’t have an engineered channel directing the air. It is possible to have situations where you chill the slab — if air can find a short path to the subslab aggregate — but in most cases the path is so tortuous, you’re not going to see any chilling of the slab.” "
As I understand it, most of the time, a radon fan is rated at 100 CFM, but it's actually working at more like 20 CFM, depressurizing below the slab, but not moving that much air, except in the cases where there is highly permeable soil or other ways for outside air to get under there.
I am about to lay radon pipe in my crawlspace to try a Passive sub-membrane sunction venting. I can only place the vertical pipe on one corner on north-west corner of home.
I can either go thru the interior floor and up about 8' thru the interior and then out, or go through the floor header/rim joist and go up the exterior wall. The interior option is best for moisture protection in my case because that corner seems to be my most moist ground area. It may provide more pipe warmth since it will be heated for that 8-9'.
I can't place the pipe through middle of the house space for best stack effect. It has to be this corner.
Which would be best for passive airflow draw? Inside corner pipe run right?
Also, I thought instead of going only 1-2 feet over the roof edge, I'd go about 10'-12', since I have a large antenna post on this same corner I can attach to. Does the taller pipe likely increase air draw from under the membrane? Sort of like stack effect on a woodstove?
Is there a reason I can't use 2" PVC pipe that I already have for the 26' x 35' crawlspace area? I plan on outlining the footprint and also putting a section down middle that is all connected. About 160' of 2" ABS irrigation plastic pipe, with 1/2" holes drilled every 1-2 feet in a spiral pattern.
My vertical pipe on the exit end, from the CS floor to the roof, would be 3" or 4" schedule 40 PVC or ABS. Black ABS might draw more heat on sunny days, but is that good or bad for the natural air flow I want?
I have an electronic tester for results/changes. If passive does not work I'd add a fan on the roof eave and see what that effects.
My CS is sealed fairly tight, with insulated CS sealed doors and vents. I would put a double bead of construction adhesive 18-24" up my CS interior walls, and allow some slack in all directions for access cuts/mending if later a sump pit or radon pipe maintenance is required. Later if radon vent goes well I'll rigid insulate my CS walls.
If my CS is the only source of radon house peneteation, will this design likely suffice with the horizontal pipe 2" and the vertical being about 22' of black ABS? There is so little design science on this matter. So I guess work experience is all we have, lol.
I also have some leftover drainage material I can place the pipes on and also strand runs of it perpendicular to pipe in areas. That should further increase my free flow suction footprint considerably. If this would work I'll be stoked. Only thing I'll have to buy is 3 sticks 4" PVC and connecting piece.
Oops pic
To be exact 191' of perf 2" horizontal pipe and 23' riser (5") from CS floor to top where it meets sky. And I think I'll use a 5" riser, instead of 3 or 4". I think this will increase natural draft.
From one source I checked if I have a 20deg F difference in temp from CS sub - membrane temp (~40 degrees F with plastic down, i project) to top of stack, I should have at least 3 pascals of pressure difference. Is this enough draw to be effective and expel the radon trapped by the membrane?
Andy,
Q. "Which pipe location would be best for passive airflow draw?"
A. It's better to run the pipe up through the interior of the thermal envelope (where it is warm in winter) than it is to run it up the outside of your wall.
Q. "I thought instead of going only 1-2 feet over the roof edge, I'd go about 10'-12', since I have a large antenna post on this same corner I can attach to. Does the taller pipe likely increase air draw from under the membrane? Sort of like stack effect on a woodstove?"
A. There are two concerns with your suggestion: (1) The pipe must be well secured to a very strong post, to make sure that it can resist wind, and (2) The aesthetics sound ghastly. But it's your house.
Q. "Is there a reason I can't use 2 inch PVC pipe that I already have for the 26' x 35' crawlspace area? I plan on outlining the footprint and also putting a section down middle that is all connected. About 160' of 2 inch ABS irrigation plastic pipe, with 1/2 inch holes drilled every 1-2 feet in a spiral pattern."
A. I think this is a very bad idea. 4-inch perforated pipe is cheap. It's never going to be easy or inexpensive in the future to demolish your slab to fix the errors you made before the slab was poured, so for heaven's sake, use 4 inch pipe and do it right the first time.
Q. "If my crawl space is the only source of radon house penetration, will this design likely suffice with the horizontal pipe 2 inch and the vertical being about 22' of black ABS?"
A. As I wrote in my article -- which I urge you to read -- there is no way to predict what your radon levels will be. The only way to determine your radon levels is to test them after the house is built. If you end up needing a fan (or if you end up needing to cut trenches in your slab to install 4-inch perforated pipe), that's what you need to do.
Q. "From one source I checked if I have a 20deg F difference in temp from CS sub - membrane temp (~40 degrees F with plastic down, i project) to top of stack, I should have at least 3 pascals of pressure difference. Is this enough draw to be effective and expel the radon trapped by the membrane?"
A. No one can predict your radon levels. As I wrote in the article, follow the recommended details, using 4-inch diameter perforated pipe and crushed stone, and a solid riser pipe to above the roof level. Then test when your house is finished.
Thanks. This is an existing house, and the 2" pipes would be installed over drain tile sheets under a plastic membrane to allow "sub-membrane" suction.
There must be a way to determine how much more 2" pipe is required to match or surpass 4" collection pipe? Most radon companies only use a few feet (like maybe 30', if that) of 3" or 4" collection pipe. If I use 3 or more times that much in 2" pipe and have good sub-membrane circulation to the pipe collection inlets, shouldn't it be as good? I can't find any such reference to calculate sufficient pipe collection length vs diameter on the Internet and none of my 3 radon companies could answer this either.
I don't think the design recommendations are based on much analysis. They are more based on precedent. So I would see nothing wrong with using the 2" pipe, given that you aren't committing to it by putting it under a slab. If you want to go all out on giving it capacity for dealing with anything, you could use the fact that six 2" pipes in parallel have about the same flow capacity at a given pressure drop as one 4" pipe, so you could split out into 6 branches immediately where you connect to the 3" or 4" riser. The soil air permeability is usually the limiting factor, not the pipe, so I wouldn't worry too much about the pipe, and I think that the drainage material is a great idea. It would have a similar effect to having a layer of gravel, but is easier to carry down there. I'm not sure which would be more likely to puncture the plastic when you walk on it--gravel or drainage mat--but that's the only downside I see.
In theory, having a stack the same height as the house heated to the same temperature as the house would produce the same stack-effect pressure that the house itself produces. The stack effect of the house can be the culprit in sucking air out of the soil, and so matching that can, in theory, elminate that effect. It can even be a little better: If the house is decently air sealed at the attic, most of the stack effect pressure is at the ceiling plane and there's less pressure left to suck on the soil. So you can, at least in theory, get the sub slab pressure below the basement pressure with a passive system. But that assumes the sub-slab (or sub-membrane in your case) region is an open cavity, mostly sealed from the outdoors and from the basement or crawlspace. It's not so heat an tidy in real life--there's dirt blocking flow between the different regions under the slab, and there's leakage between that space and the outdoors and the basement. So it's very unpredictable, as Martin says.
With a vigorous flow in a chimney, added stack height above the roof helps increase draw. The flow in a radon system is usually, and ideally, very low. So the air in part of the stack above the roof might cool all the way to ambient, at which point it doesn't help the stack effect at all. It might be possible to insulate the stack and keep the air in it warm all the way to the top, but if the edges of your membrane are well sealed, the flow will be low enough that it's likely to be cold in the stack even with insulation.
The passive nature of a stack-effect driven vent is appealing, but it's not truly passive. You are supplying energy in the form of heat from the building's heating system. That's a very low efficiency way to move air. On the other hand, typical radon fans use low efficiency motors running low efficiency fans operated way off from their best (but still lousy) efficiency point. That's because the actual impedance of the sub-slab airflow path in unpredictable and nobody I know of matches the fan selection to measured characteristics. If your motivation for sticking will passive with a tall stack rather than adding a fan is saving fan energy, you could dig into matching the fan to the measured characteristics to optimize the fan selection, as another way to save energy without the problems Martin and I have noted with the tall stack.
This is what I've found so far in last few weeks of planning repair. No one knows how small the pipe diameter with acceptable air infiltration holes the pipe can be. But does anyone know if there's a maximum diameter I could install? Would it be OK if I laid 5" schedule 40 pvc, but less of it, like 70 feet, with the drainage material? Any idea on how much required of 5"? For my CS sq footage?
I don't want to do this twice because I hate being down there, lol, so I want the best results for passive system to be done with it.
Another idea I had...put a single 2" to 5" section breather pvc with one way air flow valve on the opposite corner of CS, that is opposite the 5" vertical exit chimney. It would allow the stack to work better eh? By allowing intake air into the horizontal collection pipes? In winter I'm not sure how much cold air would be induced to CS through the plastic membrane. Probably a drawback, unless I insulated the floor with sprayfoam, or membrane with rigid foam. Or maybe simply two pieces of 12mil membrane with insulation sandwiched between would work well enough. Then I might as well fill it with water and have a small lap pool in the CS, lol.
Or what might a second chimney induce into the passive system? On opposite corners of the CS? Either equal heights or regular 1' above roofline.
If my first stage passive doesn't work I will try this breather concept, and what the hell, the second chimney as well. I have an existing 3" pipe I can tap that goes out of the CS just below the floor joists so it doesn't compromise the radon membrane. If it doesn't work I can remove fitting.
If anyone knows anyone that retrofit a passive radon system please connect me. If this can work in certain situations it might save a few ships of coal from China for the electric company as well as be easy to DIY install. The most popular mitigation practices seem to work about 90% of the time, but with electric and service costs. I hate electric bills. I like quiet passive.
Oh, the black 5" radon chimney would be attached to a large antenna post that cemented into the ground. I already have the ugly rusty antenna, another black pipe no biggie to me.
Thanks for the suggestions. Just figured out that 5" PVC/abs isn't carried by most places. So I'll use black ABS 4" as the vertical vent pipe, and initially see what that alone does, if its just running down to crawlspace exposed dirt floor, resting on a 90deg elbow. Then if necessary I'll lay plastic, leave it unsealed and retest. Then the additional pipe sections if needed, retest. Then seal the plastic over the pipe, and retest. If all tgat doesn't work I'll add a fan. The joys of home ownership in a rural high cost area, lol. At least I get to experiment and feel like a scientist!
I believe the vent pipe above the roof line, after it travels a few feet away of the interior wall, will likely get chilled in the coldest winter times. That may indeed hamper vent draw.
I have to run radiant oil heaters sometimes during those couple of weeks and could place one next to the interior pipe of that room to see if that did anything to help it stay warm. But that's thinking ahead.
Hopefully the combination of the CS being sealed well from the upper house, and the membrane being sealed from the dirt under the CS also (with adequate air flow underneath to collection piping) will be good enough most the time, if not all.
I'll let you folks know how it goes. Thanks again!
.
So I drilled a 6-inch hole through the slab and found a plastic sheet (vapor barrier) on the underside of the slab. Does it do anything in terms of reducing radon leakage through the slab? Because now I am questioning whether the high radon was coming from under the slab or somewhere else.
Joe,
A layer of polyethylene under the slab is always a good idea, and the poly certainly does no harm. But a layer of polyethylene cannot prevent the entry of radon.
The driving force that pulls radon into your house is the stack effect. The stack effect depressurizes a basement, pulling soil gases into your home through tiny cracks in your foundation: the crack between your slab and your walls, invisible shrinkage cracks in the concrete slab, and cracks around any plumbing penetrations in your foundation walls.
Some typical solutions for cases like yours are described in my article, All About Radon.
The most common solution is to install a 4-inch riser pipe connected to a void under your slab, and to use a continuously operating exhaust fan to depressurize the sub-slab zone. I strongly advise you to hire a radon mitigation contractor to help you.
Just to report back that I've finished the radon system myself and right now the level is between 0.7 and 1. Pretty amazing for a small fan (RP140).
Joe,
Congratulations on your results. I'm glad that everything worked out.