• Services for Bill Rounds
    If you haven't seen it already a memorial fund has been set up for Bill's family. If you wish to donate here is the link.
  • Services for Bill Rounds
    Bill the world is a lesser place without you my friend. Missing you deeply. Thank you for being my friend and colleague. You will be remembered. Rest easy and go with God :broken:
  • Are these changes needed?
    Hi Jeff. I agree with you 100%. ASHRAE to residential radon isn’t apples to apples. The reason that the Canadian radon discharge clearances so closely match direct vent gas appliances is because the science of dispersion, re-entrainment and exposure are so very similar. With combustion appliance discharge we don’t see significant re-entrainment and we don’t see exceedance of acceptable carbon monoxide (CO) exposure limits indoors.

    Thanks for the input Shawn. I have also sat on several guideline and national standard committees here in Canada and I agree with your comments. But in these committees decision is by consensus and may not reflect all opinions or all science. In several cases I have seen over prescriptive measures introduced due to a lack of information, fear that the best method won't get implemented properly by trades or simply an overabundance of caution. These are all good intentions when protecting health but they can also become frustrating and excessive.

    It is essential to note the difference between ICI (Industrial, Commercial, Institutional) buildings and residential dwellings (i.e. houses). Industrial process exhaust and residential radon exhaust need to be looked at very differently. Yes, the attached ASHRAE document is sound environmental, mechanical, and building science engineering, but industry (i.e. residential building code) doesn’t use ASHRAE ICI standards of exhaust discharge for residential combustion appliances. Instead prescriptive clearances are provided that control adverse re-entrainment. One could try and apply the ASHRAE ICI standard to CO from combustion appliances in a residential setting as these effluents are technically covered by those standards but we don’t because those standards simply don’t apply to residential. It would be far too cumbersome, let alone unnecessary, for a mitigator to do all the math to apply ASHRAE ICI to residential.

    ICI discharges need and were developed to address point of impingement (e.g. fence line) exposures for a whole host of acutely toxic substances with short term exposure limits (STEL) and ceiling limits. This is vastly different to chronicly toxic substances with long-term weighted exposure limits such as radon. Even POI concentrations for chronicly acute substances are based on 24/7 365 70 year exposure risk base. I am not saying “its only radon”, I’m saying use proper industrial hygiene science and proper building science together.

    ASHRAE does mention radon in several of their standards but in my opinion these documents were never intended to deal specifically with radon but more so other acutely toxic substances. As a result they tend to confound things. The challenge, as Shawn has indicated, is that they may be general reference or even cited standards and therefore may have some legal bearing or perceived legal bearing.

    As we know, and as demonstrated by Bill Broadhead and Canada NRC we don’t see radon above the action level re-entraining into buildings at the action level at 6ft (2m). Furthermore even if we did see a spike of radon at the window face or a spike of radon re-entrain into the building at or above the action level, that does not mean weighted radon levels have been exceeded and that an overexposure has or will occur. If we are overly worried about a transient episodic re-entrainment of radon we misunderstand what an average weighted exposure limit is. For example, just because you have smelled second hand smoke a few times it doesn’t mean you have been overexposed and it doesn't mean you will get lung cancer from it, the same applies to radon. I am far less worried about a tiny episodic re-entrainment of radon then I am about a system icing up because of too much exterior piping and resulting in elevated indoor radon throughout the building for a number of days or weeks.

    Recently a few colleagues and I looked at an exhaust on a new construction radon system. Someone was using ASHRAE 62.1 2019 to impose a prescribed 30 ft (10m) minimum radon exhaust clearance criteria. Well this standard also permits you to calculate the required clearance instead of picking the 30 ft from the table. Well we did the math and came out with 6ft (2m) which is what the Canada NRC study and Bill Broadhead also figured out with experimentation.

    We need to make sure we don’t take the word “toxic” out of context especially without an associated exposure or dose component. As Paracelsus, the father of toxicology, said “Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy.” In other words the dose makes the poison. And yes radiation and radon have a no threshold dose limit but let’s put it in perspective for the goal of the mitigator, our industry and this thread.

    In the linked publication under the Toxic Stack Exhausts it clearly focuses on substances with rapid and acutely toxic effects (i.e. lab fume hoods and carbon monoxide from large output combustion appliances). These discharges are very different from a residential furnace, water heater or dryer or residential radon system. This takes us back to Jeff's comment above about the Canadian radon discharge clearance matching the gas appliance discharge clearance which matches Bill and NRC findings. Coincidence.......I think not. LOL
  • Are these changes needed?
    I can't speak to the additional piping support changes and I would agree that if it is not full of liquid then you don't need a lot of support.

    As for discharge locations I support a ground level discharge and how we do it up here in Canada. There is sound research, Bill's included, that demonstrates little to no re-entrainment. Of course use sound judgement and treat each site specifically (e.g. carefully consider a ground level discharge if the only available location is beside the kids sandbox). One of the benefits of ground level discharge is a short pipe run on the exterior which dramatically reduces the chance of freeze up in cold climate. If our goal is to reduce indoor radon the last thing we want is a plugged system at the time of year when indoor Rn is at it's highest.

    When you look at the Canadian design process and the correction factors for stack effect it is a very useful tool. If I did an install in the peak heat of the summer when stack effect is lowest and didn't adjust my design to compensate for drastic increase in stack in January I would be concerned about the not having sufficient delta P. I may get lucky with washout but to rely on that is poor engineering. I can see less need for this in the warmer states.

    I would be interested in looking at the the difference in stack over a day in a desert climate where days can be very hot and nights can be brutally cold. In theory you would design and install your system during the day in the peak heat/lowest stack effect time.

    As for recoding site information (i.e. post mitigation delta pressures) I can't stress enough how important good documentation is. I look at it from a contractual and liability standpoint. Good documentation is proof positive that you did what you were retained to do and that you met a standard or best industry practice. Pressure readings are quantitative where smoke is qualitative. If the owner isn't happy and has another party come in to investigate your work you have something showing you did it correctly and you were "duly diligent". In my mould consulting days I testified at a case. The contractor was a mom and pop outfit known to me and he was an honest and qualified person who I had seen do excellent work in the past. In fact he did a good job at the site in question. But when it came to notes he was not the most diligent. The lawyer utterly crucified him on the stand and he lost ALL credibility and eventually the case because his notes were garbage, just some numbers jotted down on the front of the project file folder YIKES! I felt so bad for him watching it unfold and not being able to help him. On the other hand I can count two times when my note taking and standardized forms/process prevented charges or a court case and one time when my notes got a case dropped. Moral of the story, he with the best notes wins. Legal people like to see standardized approaches and standardized forms as they show you put thought into what you were doing even before you stepped foot on site. The alternative is a cowboy approach shooting from the hip. Regardless on how qualified you are, at that point, you run the risk of looking like an amateur.

    I run a national radon measurement and mitigation program in Canada for several banks, large commercial clients, government buildings, etc. When I have a site mitigated it is a requirement that I be provided the natural and post mitigation delta P across the slab. I use this data to ensure a good system installation but also to protect my firm and the mitigators that work for me.
  • Mitigating with French Drain and Weep System
    I think Rob is suggesting something like the solution in Fig 3 of the link below or attached picture.

    Both are from Building Science Corporation and Joe Lstiburek. Cruise his web site as there are lots of articles and designs free that you can take to building officials for approval. Joe is a well known and extremely qualified building scientist so using his design may get you traction/acceptance that you would not otherwise get.

    Of course these assume you have access to the foundation wall. You may need to modify the drainage sheet depending on how it is installed. Just be careful that the drainage path drips freely below the slab, otherwise the concrete will absorb the water and the slab move moisture (just like if your radon pipe doesn't protrude below the slab to make a clean drip edge).
    Block Wall (331K)
  • Alarms are mandatory now on radon systems
    I have been following this with great interest as I sit on a CSA standards committee for infection prevention in healthcare. Standards are a tricky thing to right and you will never please everyone. In My experience is that there is little feedback during the public review process and lots of concerns/complaints after the publishing of the standard/guideline. In our committee there has been many heated debates. We often reconsider our opinions by remembering that our ultimate goal is protecting human health, which is what radon mitigation is all about.

    I think there are two distinct concerns raised here.

    1) Legalities that alarms and home test devices will pose liability to the mitigator.
    2) How will I manage all my false alarms and client expectations.

    Both are valid concerns but one is a legal argument while the other is a business management issue. Standards and guidelines need to reflect current science and technology.

    I am no lawyer but; it would seem logical to me that the installation of any additional device that alerts an occupant to a real or potential health issue (chronic or acute) would reduce liability even if it was prone to false alarms. If we look at the legal definitions of "due care" and 'due diligence"

    due care
    n. the conduct that a reasonable man or woman will exercise in a particular situation, in looking out for the safety of others. If one uses due care then an injured party cannot prove negligence. This is one of those nebulous standards by which negligence is tested. Each juror has to determine what a "reasonable" man or woman would do. Source

    due diligence n
    1 : such diligence as a reasonable person under the same circumstances would use
    : use of reasonable but not necessarily exhaustive efforts called also reasonable diligence NOTE: Due diligence is used most often in connection with the performance of a professional or fiduciary duty, or with regard to proceeding with a court action. Due care is used more often in connection with general tort actions.

    You can educate an owner all you want but they may never check their U-tube or may never retest their home. Alarm technology exists and can alert to a potential health risk. I think a judge or juror would find that a reasonable action. If the plaintiff (who has lung cancer) argued "due care" in a tort claim and you installed a low cost alarm I think it is clear your were a reasonable person who exercised all available options in this particular situation, in looking out for the safety of your client.

    On the other hand if you didn't install an alarm I am not sure how it would work out. I think in any case there is a good chance of a claim being paid out. But the more care you take (i.e. install alarm) the less the claim will be.

    If you are concerned about calls and all the client risks what options to you have to controlling the freeze ups. Has anyone looked at installation a pipe heater similar to a gutter/roof deicer on there systems. Instead of telling the homeowner to hush the alarm for 3 months you could tell them to plug in the heater and give it some time. As my structures professor always said "We can engineer anything for everything".
  • Smoke testing of membrane below a slab.
    Like Brooks I was going to recommend a stage smoke machine. I have used them in the past for haz mat containment confirmation. They pump out lots of smoke. Lots of models available on amazon for under $100

    To manage the pressure try an inverted radon fan and add a router speed controller to dial it down to exactly the output you need about $30. You can even get inline duct fans with built in speed control. Here is an example of both on amazon just scroll down to see some options. I suspect just about any model will do for your needs
  • I have 2 questions.
    Hi George. you said you "will also include a small fan unit on the side of the house to draw air out of the closet space and vent outside in case fan unit or fittings leak in closet area". I am not sure this is necessary or even a good idea unless it is required in your area. An unoccupied attic should be well vented anyway. I think a set of passive vents in the closet (one at the top and one at the bottom) or additional passive venting of the attic (still meet your local code requirements though) is better. Typical breezes and sun on a roof result in a significant amount of venting and should dilute any small to moderate radon leak (plus there is no one occupying the attic). Adding a powered fan to an enclosed structure that is not fully designed for it can do all kinds of funny things with heat and humidity that can cause a bunch of other issues (rot, freezing, condensation etc.). My fan sits in my garage and I have had no issues, of course Bob Wood installed it so the thing is mounted for gale force winds :). Bob does great work!
  • I have 2 questions.
    Hi George. I am a certified building scientist and radon professional and I like your plans for your house. I have foam board under my house which meets LEED gold standard and my radon was still elevated. An active system lowered it nicely.

    If you are doing 2" of foam board plus 10-20 mil poly tape sealed under-slab (which is a ton of work by the way) consider using 2" minimal of 2lb closed cell spray foam instead.

    The sprayfoam underslab will be a single application insulation, vapour barrier and air/radon barrier. The material cost per square is a bit more but the sheet insulation and poly method will have significant labour costs. We find the reduced labour cost of sprayfoam installation more than offsets the increase in material cost.

    What is important to realize is that the lions share of radon entry is by mass transport (i.e. air/soil gas leakage from holes, cracks, missed seals etc.) and not diffusion. Typical construction and even super duper great construction lack the sealing detail and workmanship to make a perfect or even good seal. I have seen thicker membranes, like the 10 to 20 mil poly you plan to use, placed under slab and the increased thickness of the make the sealing details at penetrations and corners very difficult as the material bunches up. This increases the chance for leakage. Expanding sprayfoam on the other hand makes as close to a perfect seal as humanly possible. This great seal will mean that you can use a smaller radon fan to get better pressure field extension or in other words, less energy & better radon control.

    Some brands of 2lb closed cell have been tested as a radon barrier and it out performs poly for radon diffusion by at least 4 times and potentially up to 50 times depending on thicknesses of poly and foam. If I had it to do over again I would have put spray foam under my slab but this was not a builder option. In Canada a government approved method has been developed for sprayfoam radon barriers underslab. See the attached documents and link below. The radon specification is the 5th download listed.
    CCMC-14073-R_EN_RADON-RCS (781K)
    Demilec Spray Foam Suitability as Radon Barrier (2M)
  • How would you improve this Rubble Stone Wall mitigation?
    Hi Tom

    Some of the guys who have commented my have some contacts for you for good sprayfoam contractors. If not I found a few US groups that may be able to help. I have also listed the Canadian Association (CUFCA), which won't have members in the US but they likely know their US counterparts and could help.

    3927 Old Lee Hwy. #101B
    Fairfax, VA 22030
    Tel: (800) 523-6154
    Fax: (703) 222-5816


    In Canada

    Andrew Cole at CUFCA may be able to direct you to someone
    3200 Wharton Way
    Mississauga, Ontario, Canada L4X 2C1
    Toll Free: (866) 467-7729 (1-866-GO-SPRAY)
    Toll Free Fax: (877) 416-3626 (1-877-416-FOAM)
  • How would you improve this Rubble Stone Wall mitigation?
    Hi Tom

    You could sprayfoam the foundation walls.

    I agree that an ERV or HRV would work and could be a cost effective installation. I noticed there are ducts in the basement already.

    Emanation from the foundation wall could be a source however I would suspect that radon ingress through the foundation wall to me more likely. Stone foundations can have many pathways in them.

    Some sprayfoams have been tested and approved as radon barriers and are much more effective then 6mil poly vapour barrier (or any other membrane for that matter) from both an air leakage and diffusion control perspective. I have attached some supporting documents and details for you.

    The spray foam would control radon entry and emanation from the foundation walls by diffusion and soil gas leakage. In addition it would likely improve negative pressure under the slab. As Dick mentioned you seem to be pulling a lot of air which could be drawn from the basement through the foundation walls. The sprayfoam would really seal that up.

    Another benefit with the sprayfoam is that when you place the drainage plane over the foundation (done before you spray, see the attached detail) you end up with a tiny gap between the foundation wall and drainage sheeting. If you tie this gap into the SSDS via the sheet metal channel you gain active depressurization along the entire wall face.

    The sprayfoam system would certainly be more costly to install but it would use far less energy over it’s life span than an ERV/HRV and would offere other passive control measures that the ERV/HRV wouldn’t. Two things I don’t like about ERV/HRV is they can be shut off by an occupant and they are also maintenance heavy. If the owner is not cleaning filters or intakes regular (every 3 months) then is losses its effectiveness. Don’t get me wrong…I have and HRV and love it. But I am also an obsessive indoor air quality professional who runs and maintains it properly.

    Here are 2 links and documents for reference. The first link is the CUFCA and NRC approval of spray foam as a Radon barrier in Canada. The second link is the detail for spray foaming a rubble foundation wall which includes a drainage plane between the foundation and the wall. You will need to confirm local fire code requirements for what the foam needs as a fire barrier. Building Science Press and Joe Lstiburek are renowned for their competence in building science. I can't imagine a building official being able to argue with his designs but check first.

    If you sprayfoam you must make sure occupants are out of the building during the application of the spray foam. This doesn't sound like a problem in your case. The isocyanates in the foam are a chemical sensitizer and you simply must control exposure during application.
    CCMC-14073-R_EN_RADON-RCS (781K)
    Rubble Foundations _ Building Science Corporation (939K)
  • Foam retarding Radon entry.
    To add to Bob's comments spray foam is fantastic for air/gas sealing. Here are 2 links and documents for reference. The first link is the CUFCA and NRC approval of spray foam as a Radon barrier. The second link is the detail for spray foaming a rubble foundation wall which includes a drainage plane between the foundation and the wall (which Bob suggested you have for other valid reasons). You will need to confirm local fire code requirements for what the foam needs as a fire barrier. Building Science Press and Joe Lstiburek are renowned for their competence in building science. I can't imagine a building official being able to argue with his designs.

    Bob already mentioned it but I also need to repeat it. Make sure occupants are out of the building during the application of the spray foam. The isocyanates in the foam are a chemical sensitizer and you simply must control exposure during application.
    Rubble Foundations _ Building Science Corporation (939K)
    CCMC-14073-R_EN_RADON-RCS (781K)
  • New Radon Fan use
    That is awesome!
  • Sealed poly in Passive Crawlspace System
    I have not had direct experience with that happening to a passive radon barrier but I do have lots of experience with sealed poly and pressure difference in buildings and air tight buildings. This could totally happen. I see two ways to stop it. 1) ballast on top of the poly, which has pros and cons to consider, or 2) activate the system like Rob implied. My house is so tight (entirely insulated with spray foam) that the water in the toilet goes up and down with the wind and even with slamming of the door to outside. This is a delta P of up to an inch of w.c. it would take a tiny fraction of that to flap poly.
  • Urethane or silicone as sealant?
    Clean and dry surfaces are also key. I have seen urethane peel off with zero effort at the cold joint and saw cuts. Simple issue of builder not following instructions.
  • No correlation?
    I notice that he does not cite his reference. If one is to refer to a study they should reference it. I would contact him and ask him what information he researched before making his conclusions.
  • A new one on me
    I would get this all the time with people smelling asbestos, silica and lead. It is just anxiety about health and people not understanding the science. Take the high road and use the opportunity to educate them.
  • Rubble Stone Walls
    I don't envy your task. Items 1 to 3 seem straight forward enough but items 4 and 5; wow! Good luck. As we all know Items 4 and 5 can certainly be done but trying to find a low cost solution and provide accurate cost estimates will be difficult. I wonder, would you have some luck discussing the pros and cons with the client? If you explain that passive Rn controls have low effect and the challenge and cost with sealing rubble walls they may be more inclined to go to an active system. As Jay eluded active slab depressurization seems to work in controlling radon intrusion through rubble walls for him.

    If the walls prove to be a significant source of Rn intrusion, even after sub-slab mitigation, you could consider an active wall system ( e.g. depressurize or pressurize a cavity created by dimple board placed on the interior of the rubble wall). The active system would manage any imperfect seals in the dimple board. You could have the cavity drain to the soils below by drilling holes through the slab at the base of the wall and ensure the dimple board covers the holes. Make sure you drill enough holes to manage the anticipated water and get the low spots in the floor. You would need to make sure that the negative pressure under-slab is greater than the negative pressure on the wall cavity so that water pooled at the bottom of the wall is not slurped up into the wall because of back-draft up the drainage hole. Again there is lots of buildings science to consider with pulling or pushing air/soil gas through the foundation wall. If you pull too much cold air in from outside you could cause some wall freezing. If you pump too much warm air into the cavity you could warm the exterior soils in the winter (no so bad but lots of energy loss).
  • Rubble Stone Walls
    Dick. I know Bob very well and we talk about this stuff all the time. I am a certified Building Scientist and Certified Engineering Technologist in the Civil discipline. I don't know the full scope of your task or budget expectations which put me at a disadvantage. The foam is simply a tool to provide a very effective air barrier/radon barrier. It is an option to use or disregard as you see appropriate to your project parameters. You are correct that the insulation is not "needed" but in your case the foam is the radon barrier/membrane and the insulative value is just a side benefit. In Bob's example (and likely Joe's for that mater) I am sure the drainage plane (dimple board) was not sealed and they relied on the foam as the seal. You could try and manually seal a rubble/stone foundation wall manually but I would expect labour cost to be very high and efficacy of the seal to be very low. A low seal efficacy would not be good particularly if you are looking for passive controls as you indicate is the goal. But perhaps there is a migrator out there who can do an adequate manual seal at reasonable cost. Building Science is a very, very, very complex thing. Managing moisture and it's movement in any building envelope needs to be considered carefully as do budget implications. In Joe's French drain configuration he is managing moisture in the wall and providing a free and clear drainage path to the subsurface. It is important to not that you would still have to provide a membrane barrier on a rubble wall a place to drain any accumulated water as you can't simply let it pool at the bottom of the wall with no where to go. Lstiburek and his firm is available to consult on projects.
  • Radon Diffusion Coefficient Testing
    David is correct. Czech Institute in Prague is best bet. My contact there was Martin Jiranek email

Bruce Decker BGIS

Start FollowingSend a Message