Radon in my Conditioned Crawlspace
Dear GBA friends,
I just finished reading “All about Radon” with the comments as well as a few other articles. Thank you for the advice.
I wonder if my situation would have been less problematic with a vented crawlspace rather than conditioned. Anyway I have an unvented crawl now. House has been built over the last 5 years, and I moved in 2 months ago.
I installed a 10 mil vapor barrier, taped at seams, sealed to concrete stem wall with adhesive and pins (https://crawlspacerepair.com/crawl-space-foundation-pins) at least 12 inches up. Under the plastic I laid down landscape fabric to protect the plastic from the 3″ round rock. There are about 4-6 inches of this round rock throughout the crawlspace.
Obviously there are no vents in the crawlspace wall to the exterior. I have 3 vents between house & crawlspace and was about to install fans (with inline carbon filters for minor smell) for intermittent air circulation. Crawlspace temps are about 55 degrees F and humidity in the 70% range. Would be good to get it closer to the house which is 65 F and generally 55-50% humidity.
I’d hesitated to install the air circulation due to the minor but noticeable smell, ordered the carbon filters from ac infinity. Then thought of testing for radon.
Radon in the crawlspace comes back at 24.4 pci/L (2 bottle short term tests https://www.prolabinc.com/radon-gas-test-kit/). Tested the interior of home and results are 10.5 pci/L (average of 2 bottles).
So. This is high, but crawlspace (I’m ashamed to admit) has been unvented for quite some time (although it has the liner). During dry summer months I’ve often run fans and generally aired it out some.
So I’m living in a house with 10 pci/L. I have contacted two remediation companies, first one quoted me $5700 which seems high (no visit to my site). So I’m waiting on a 2nd company and a site visit this week.
Is it worth doing a 3 month test right now, or should I move straight into investing in remediation?
Question 1
Is it responsible or irresponsible to wait for 3 month test results before acting/remediating? I am living in this space already.
I have ordered the 3 month test from prolab. I can also pick up a 2nd short term test but at this point i have 4 bottles confirming my levels are elevated so perhaps it’s a non issue.
Any money I throw at this seems cheaper than lung cancer. At the same time I don’t want to panic and waste money.
I am likely to proceed with remediation, and I would LOVE to be able to resolve my issues with a passive system. I do not have an attic, so I eagerly await the conversation with the remediation contractor (https://cascaderadon.com/ of portland OR) regarding the specifics of whether this can work. I think adding a fan if passive is insufficient seems doable as a follow up.
Question 2
I did read about the HRV in the crawl as another possible approach. Should I add that to the mix or just start with a passive system? How do I think about HRV conjunction with remediation. I did a blower door test a while ago and we concluded that my house is not quite air tight enough to recommend using an HRV system.
Question 3
I think the 10 mil plastic I have now is already sturdy enough to be used for the depressurization system. But one company specificed 12 mil plastic, a special type. Opinions on that? If I use what I have now I forsee the contractors cutting holes in it to install the pipe, then re-sealing the cuts.
Question 4
type of pipe for depressurization system. I used sched 40 perf pipe around the outside of my foundation for foundation drains. For the radon system, first contractor said perforated schedule 40 pipe. 2nd contractor said socked ADS pipe, which doesn’t sound as strong. Strong opinions on these options?
Question 5
I have a centrally located utility closet, but the question of how to get a pipe up & out of the house with minimal turns seems tricky, and I hate to cut holes in the roof. Run a pipe up an interior wall and then exit high in the wall? (it becomes an exterior wall further up) I might have to show drawings to make this make sense.
Thank you all, I’ll keep you posted and watch this space for replies.
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Replies
I wouldn't count on an HRV as the primary method of radon reduction. I'd rather get it out of the house before it enters the crawlspace air (and house air since they are connected). The 10 mil plastic should be fine if it's in good condition; I don't see any reason to replace that. Either type of pipe should be ok as well. If it is difficult/expensive to get a pipe up through the roof, then you could go right to an active system with an exit out through the rim joist.
I think you're going to need an active system with your levels -- a passive system is probably not going to be enough. I also think you should go ahead with the remediation system installation now, and not wait on a 3 month test. Your levels are very high, so I doubt very much another test is going to show enough difference to get you into the safe (>4 pci/L) level.
I had a somewhat similar situation to you, where I tested my crawlspace prior to encapsulation. My test results (using a lab test) were around 8.1 pCi/L. I put in an active system using the existing footing drain by sealing the sump pump and coring the basement slab to tie into the drain. I'm not consistently down under 1 pCi/L, usually much less (0.2-0.3 pCi/L is typical), even though I haven't finished the encapsulation project yet so the vapor barrier hasn't been laid down. My plan is to run some perforated corrugated pipe around the perimeter under the membrane so that the crawlspace becomes a second "zone" for the radon system, and I have the radon fan plumbed for this already.
The pipe doesn't need to be particularly strong, since it isn't going to be taking any real load. The radon fan is going to pull maybe a few inches of water column worth of negative pressure at maximum, which isn't enough to collapse any type of drain pipe you're likely to try using here. The corrugated stuff is easy and fast to install, and is also cheap, which is why I'm using that. All you need to do is to depressurize the earth underneath the vapor barrier, so you don't need anything fancy. I'm just running a loop of 3" pipe around the footing in a C shape on the outside wall away from the connected basement, since that area is already covered by the "primary zone" for the radon system.
Regarding your specific other questions:
1- See above
2- I'm not a fan of using an HRV for this, since it is a sort of bandaid, exhausting the radon once it has already entered your home. Using an actual radon mitigation system collects and exhausts the radon BEFORE it enters your home. It does this by depressurizing the ground beneath your home, which is a bit like using a big vacuum cleaner to suck out the radon before it enters your home through the foundation walls and slab.
3- Thicker is better, but mostly for durability -- even thin stuff will work fine as an air/vapor barrier. I like to use 20 mil on the floor to minimize the possibility of damage in the future when doing any work in the crawlspace. I use a reinforced 20 mil crawlspace liner for this, and thinner material on the walls where the material is less likely to be damaged (this saves some money). 10 mil is the minimum. 12 mil would be better. 20 mil is the thickest commonly used. Thicker is better, but costs more money. Reinforced liners are less likely to tear, but are not any more resistant to punctures compared to non-reinforced liners. If you have a soft material as the floor of your crawlspace (sand, etc.), a thinner material is probably OK. If you have crushed stone, the thicker liner is better if you don't want to put down a few inches of sand as a protective layer.
4- I don't see an issue with any commonly used drain pipe materials here. You don't need super strong material since there is little pressure involved, and everything should be installed in areas where it's not subject to much risk of physical damage. I've described what I used already. The most commonly used materials in my area PVC and the perforated corrugated ABS stuff that comes in a roll.
5- This can be tricky, and depends on your home's layout. In my case, I was able to run 3" schedule 30 PVC pipe up a 2x4 studwall from the basement to the attic, so my vertical run is entirely within a wall and hidden from view. I ran two parallel runs, transitioning to 4" pipe at in the attic (where the fan is), and again in the basement. I did this because my system runs a fairly high CFM and relatively low pressure, and I didn't want flow restriction from a 3" pipe over the rather long (50 ish) foot run. If you have a smaller flow requirement, a single run of 3" pipe is probably fine. The advantage to the schedule 30 stuff is that it fits inside a 2x4 studwall, if I was running it in a closet I would have used schedule 40 DWV pipe which is usually cheaper than the thinwall stuff.
Ideally you want that vertical pipe to go straight up. Your fan would go in the attic (the fan should NOT be installed inside the home's envelope, which includes livings spaces AND the basement AND the crawlspace). Fans should be installed in attics or outdoors, which ensures that ALL the piping within the home is running at negative pressure so that you aren't leaking radon out into the house. When running negative pressure, any leaks draw air INTO the pipe, which is safer than letting radon OUT.
It's common to run vertical pipes in the backs of closets, or to exit the wall of the crawlspace or basement, then install the fan a little above ground level on the exterior and run the exhaust pipe up and around/through the eave. I prefer to keep the system hidden from view as much as possible, so I put in the extra effort to run the pipe inside of an interior wall.
Bill
Thanks! So what I'm gathering is that locating the vertical pipe in the building envelope where it stays warm is needed for a passive system. I'm guessing that even if I end up needing an active system, a warm vertical pipe provides support to the system. The trick is just locating everything in walls and keeping it with as few elbows as possible.
keeping the fan outside the envelope is good to know. I already had one contractor say they'd locate the fan in the crawlspace, but my crawl is conditioned so that's not a good idea.
The idea of having a constant background fan whine is vexing to me as I live in the woods and prefer to not have machine noise. Any tips on minimizing the noise/soundproofing options?
Thank you.
Use a good-quality fan, and try not to get one way more powerful than you need. Mount it to rigid structure, not the middle of a wall, to minimize vibrations/resonance that can make the sound worse. I don't really notice mine all that much, although I can hear it as a low background noise, somewhat like a refrigerator running. It's not very noticeable, although I do intend to try to quiet it down some more. I used MLV on the pipe between the fan and the wall in the attic, and rubber sheets between the pipe and the clamps too.
Bill
Since you have the fan coming, I would try two options. First vent the fan outside. Set it to something reasonable 1CFM/50sqft of area and see how it goes. You can get digital monitors to log and see how effective this is.
If this reduces the levels enough, an HRV/ERV would work just as well without the energy penalty.
Another option is to connect the fan to your existing poly. Remove the rocks and tape a duct collar to the poly to connect the fan. If this works well enough, you might not need a fancy collection system a simple pipe through the poly maybe with a small T pickup with a fan in the attic will do.
Thanks for these suggestions. The house is 2 18x24 rectangles staggered. I'm attaching a screenshot of the foundation plans in case anyone is enlightened by them. My crawlspace is essentially two rooms, with an opening about 4 feet high and 3 feet wide between them. I think this complicates the solution slightly, but the house itself is only 868 square feet.
Good to know about digital monitors, and starting with a small set up.
Thanks to you all, and this webpage, I have a good knowledge base now for my meeting with the contractor Thursday, and will likely have more questions after that.
The perforated corrugated pipe is sold as 100 foot (or larger) coils, and it's cheap, maybe $50 or so for a 100 foot coil of 3" or 4" perforated pipe. You'd be fine running it straight like you show on your drawing, but I'd probably have it hug the left side of the upper crawlspace and the right side of the lower one, making a sort of "S" shape tight to the inside of the footings. This keeps it out of the way if you need to crawl around down there, since it will be at the extreme edge of the crawlspace floor. Spreading it out helps with even flow, which is a good thing.
Common radon systems just use a pit under the floor as an extraction point, but my own preference is to spread things out a bit with a perforated pipe the way I described. Sometimes with a pit, you end up needing more than one to get good flow everywhere. With a run of pipe, it's much less likely you'll have any places that aren't getting good negative pressure. Seal the crawl space membrane everywhere and you should be good to go.
BTW, a 3" pipe is probably fine here, just use a tee in the middle to transition the two halves of your crawlspace to the vertical pipe going up to the extraction fan. You'll get plenty of flow that way. Using 4" perforated pipe is fine too, just bigger and a bit more difficult to work with. The entire system ends up being held under negative pressure all the time by the fan, and with a system with a central extraction point for the fan to connect to, I don't see any advantage to using the larger pipe here. If you need very high flow rates, you might need a 4" vertical pipe, but 3" would probably be fine (both are commonly used).
Note that to really do a good job, you want to use a manometer to take some pressure readings with the system running to make sure there is negative pressure across the entirety of the floor. If you have a contractor do the work, have them test a few places to be sure everything is working well. If you DIY the system, you can skip the manometer testing and probably still have a system that will work pretty well.
BTW, I use the Airthings radon monitors and have had no problems with them. My recommendation would be to put a monitor in your crawlspace NOW so that you can get a "before mitigation" reading over a period of time, since radon levels vary over time. Once your mitigation system goes online, you should see the radon levels drop to zero or near zero pretty quickly. In your home, I'd put one radon monitor in the middle of each of the two crawlspace sections. The monitors run on batteries and mine are almost a year old now and still on the original batteries. If you get their hub, you can see charts online. Without the hub, you have to connect to the monitors with bluetooth. I use the hub myself, and a few of their other monitors (such as for CO2). It's a useful system.
Edit: Somewhere on that vertical extraction pipe you'll put a radon system manometer. I recommend you put that somewhere you can easily see it, since that's the monitor that lets you know the system is working. It's usually mounted right to the side of the pipe, but it can be mounted a short distance away too, connected with only the little vinyl sense tube. Just make sure whereever it goes you can easily see it, since if it ever shows 0" WC (no negative pressure), you know the system isn't working and probably has a problem with the fan.
Bill
Thanks everyone! I had the contractor visit and waiting on a bid. In the meantime, I've been sitting with all this information.
1) Make Up Air? In discussing this with a friend, the question arose - where is the make-up air coming from, if I am sucking air from under the plastic? My house was build on a tamped gravel pad that sits on the red gritty clayish but decently well draining soil (I don't know words for soil types). I am guessing that the suction under the plastic would draw air in through the rocks. My crawlspace has daylight on the down hill side and is nestled into the hillside on the uphill side. I have a perimeter foundation drain, and rocks filling that void, so all that would be a somewhat porous area where the make-up air is supplying the radon suction system, right?
2) I'm going to order the airthings radon monitor and then perform a mail-away test to ensure that the readings are comparable. Thanks for that suggestion.
3) I had the idea to install a temporary (or first draft) system as Akos might be suggesting. It's hard for me to give up on the idea of a passive system, as I detest the idea of relying on a fan perpetually, not to mention living with a constant whine. Soundproofing should help if I need to go that route.
I have one hole in the crawlspace stem wall (dryer vent that I ended up not using) where punching out with a pipe could be simple. While this is adjacent to my bedroom (noise concern) it would be a minimal impact way to test out an initial system to see if I get a sufficient improvement.
I'm wishful that the stack effect could solve my problems. The vertical pipe would be outside the home but on the south east facing side of the house, and I could paint it the same dark brown color of the house, or even black if that helps. However, I am guessing that during the long damp winters here in western Oregon, the stack effect may not be my friend. The crawlspace is likely to be about 55 degrees. Outdoors will vary. Stack effect needs the air in the top of the pipe to be warmer than the bottom, so is this a completely unworkable idea?
I could dig two dry well collection points, one in each rectangle of the house, and pipe from there (sealing to the vapor barrier), run the pipe to a t and then out the stemwall and up, with a long vertical stack to above the roof.
Obviously this woudl be much more effective if the vertical run of pipe was inside the house envelope, as then it woudl be warmer than the crawlspace, and the air more likely to rise passively. I'm almost open to the idea of installing this adjacent to my woodstove (max heat).
The dilemma where I'm stuck is that trying for a passive system there is no guarantee that it works, and if it doesn't, then I have holes in my floor & walls. My house is basically finished.
If the passive system doesn't work, then I can easily add a fan, but the fan would be centrally located. The radon mitigation installer guy suggested the vertical stack and fan assembly be at the back of my house, adjacent to the heat pump, which would keep the fan noise well away from my bedroom.
Finally, with the vertical run of pipe - again going with this idea of a potentially passive system, is there any advantage of a 4" vs 3" pipe?
I look forward to your responses. Thank you!
Every house should have mechanical ventilation (HRV or ERV, just fans in mild climates), regardless of blower door results. Especially new buildings. No matter how "leaky" your house is, it won't be getting enough air circulation in still air. Even when it is getting enough, it may not be in the correct areas.
Hi Trevor, I think you are speaking about all sorts of things in houses (besides radon) that some of us don't test for: toxins, co2, cooking/oil fumes that impact health?
I have hesitated to add a HRV in the house itself (loath to cut holes in walls). I am using woodstove, bath fans, and vent hood...no idea where make up air is coming in unless it's the window I keep cracked by my bed.
This is another area I likely have room for improvement.
This is probably pulling radon into your house. Running at a negative pressure compounds radon issues.
makes sense. Thank you!
It's funny that there are so many products that will suck air out of a house, but where are the products to introduce fresh air? My understanding is that an ERV/HRV puts the same amount in as out, so even if I introduce that it doesn't solve my negative pressure predicament. What am I missing?
I'm heating with my own wood, so I guess just opening a window? Obviously not what the energy efficiency experts would recommend...
You can run the Panasonic intellibalance at a slight positive pressure. But to offset pure exhaust devices you you need a dedicated make up air. There are some dampeners systems that use pressure sensors to activate that might work for your application. You can also fairly easily rig something up using powered dampers, inline fans, and home automation if it’s really bad (big range hood)
A radon system, properly installed, shouldn't result in negative pressure inside the home, since it should only be depressurizing the soil BENEATH your home.
You can let in makeup air with a simple damper. You don't need anything fancy. An open window will work too, it's just not idea over the long term.
Bill
I haven't fully digested the other answers, but a few thoughts.
I'm not an expert on this, but the humidity in the crawlspace seems high and I'd even want the house to be more in the 40s and not close to 60.
Question 1
Don't bother with the mail away radon tests. Get some of the Airthings monitors (https://www.airthings.com/products/indoor-air-quality) that can measure radon, put one in the crawlspace and one on your lowest interior level. You're probably going to need some type of radon mitigation, but I think it would be fine to measure for another month (or couple) to see the radon level trends (they'll change with weather).
Question 2
While researching radon mitigation solutions for my own house, I did come across examples of people successfully dealing with their radon problem with a HRV/ERV in their basement. Active radon mitigation may end up being needed for your numbers, but I would at least add a HRV/ERV to the mix of solutions, either just for your crawlspace or even whole house (if you don't have mechanical ventilation already).
Question 5
We didn't want to cut a hole in our roof for the active radon mitigation that we had put in. We had our radon contractor run the pipe up into our ventilated un-conditioned attic (this is where the fan is), out the gable wall close to the roof, and then up and terminated just above the roof line. This kept the fan protected from the elements, no roof penetration, and minimized ugly radon venting on the exterior.
It's a good idea to use the mail away lab tests to sanity check the Airthings monitors, especially if you only have one of the Airthings devices monitoring levels. In my own system, with four Airthings radon monitors (one in the crawlspace area, one in each of two basement areas, and a fourth up in the living space of the house), I see enough variation between them to not entirely trust them for absolute radon level measurements (which is what the lab tests get you). The Airthings monitors are great for RELATIVE measurements though (measurements made over time against past measurements), to track trends. I just think it's best to use a lab test to establish the absolute (measured against a calibrated reference standard) when first getting started, and maybe once more later on after the mitigation system has been running for a while. Best to play it safe, and the test kits aren't very expensive.
Bill