Bare soil with no gap under timber floor

[ncr703]

Hi all,
I've been doing a lot of reading but no obvious answers to my situation.
I have an old ironstone house, originally 1760-ish but severely renovated in the 1970s.

I have a high radon reading in the living room of 320bq, which is 3x the target and above the "action level".

I took some floorboards up to see the situation. The floor joists are basically set into bare soil, so only a very small air gap of 2 inches under the floorboards. In other areas there's no gap at all and the boards are streight onto soil.
There is no evidence of damp soil thankfully.
There are only 2 low-profile air bricks on only one side of the 30m2 room.

How can I tackle the radon issue cost effectively? I would get a specialist but the radon industry is full of cowboys.

I'm very concerned about digging down because the floor is barely above ground level. On one side of the house I had to dig out a french drain for this reason. So, I'm afraid of exposing moisture which then cannot ventilate away easily.
I'm also concerned because this part of the house has no footings for its 2ft thick walls.

Many thanks!

 

[Cubist]

Hello and Welcome,
Considering the nature of your issue I'm surprised that this this topic is not discussed more frequently. It's particularly challenging as it's a problem in which the root cause cannot be addressed directly and all remedial measures are focused exclusively on managing the effects. Before perhaps discussing those potential remedies, and hopefully getting some input from other members, can you tell us please how many readings were taken and over what period of time?

Also, I'm a little puzzled by the photos. Some confirm that the joists are buried in soil while others above ground and mounted on shallow brick piers and you also mention a couple of air bricks. What more can you tell us about the structure of the floor? Also, can you confirm that the air-bricks are exposed outdoors and air can circulate effectively near the internal faces of these?

Cheers for now,
Cubist

 

[ncr703]

Hi Cubist,

I've had the property for nearly 2 years and have taken one set of readings. These were done with a passive sensor left in the living room for 3 months undisturbed and then sent away for analysis. The reading period was done from November-Jan. The result came back as 320bq which is too high. I haven't repeated the test as I have no reason to doubt the result given that we are in a radon risk area.

Sorry about the confusing photographs. My perception is that the under-floor "space" is sloped such that one end does have an airgap (the photo mounted on shallow brick piers) but its only ~2 inches max. There are 2x small airbricks here, spaced 1 meter apart, and they appear to be the only airbricks for the entire room. They are exposed outdoors (into a shallow trench as the outside ground-level is raised) and I keep them clear of debris. I have dug drainage to ensure water doesn't enter via the airbricks.

The other two photographs are of two different areas in different corners of the room opposite the air bricks. There is absolutely no airgap here at all.

My current thinking is that I need to:
1) Take up all the floorboards and remove a few inches of soil material to create space under the floor. This might involve add some additional height under the brick piers....maybe with breezeblocks or similar. I am a bit worried about the shallow footings though.
2) Add some additional air bricks to the opposite side of the house to promote more airflow. This is actully quite challenging with the 2ft thick walls and raised ground level outside. Any ideas? I would need to get a contractor as I don't feel confident doing that myself.
3) Insulate between the joists using PIR on battens, otherwise the cold room is going to get much colder with the improved airflow. I think it will need to be PIR specifically because the joists are not very thick and PIR has the necessary U value to make a difference.

I was trying to think about if it would be possible to put a radon barrier somewhere in the floor to encourage the radon outside instead of up through the floor, but I imagine there's a specific way this needs doing in order to avoid accidently creating rot, especially with the involvement of PIR insulation.

I would really value all your feedback on this as I feel quite uncertain.

One additional note is that I think a solid floor option with a radon membrane is probably unaffordable right now, plus the amount of excavation required for the depth needed would make me nervous about the shallow footings.

 

[Toby Newell]

First of all, you have 'no reason to doubt' = 'I have blind faith the first result is 100% accurate so no requirement to double check' = reductive reasoning, qualitative and totally unscientific. You are probably both correct and wrong at the same time. In that statistically speaking the test results are probably correct, but wrong, imho that it is not worth double checking something so potentially important to your physical and mental health. How do you know your cheap detector was not faulty? Or that the lab had made a mistake? It happens. For something that affects possible cancer risk and whose remedy may cost thousands of pounds and a lot of stress, I would, very much, absolutely, do a second test and get it checked, not to do so seems like madness.

From a scientific viewpoint radon is a gas that decays (after a very brief Polonium stop off) into lead 210 which has a much longer 20yr + half life and also gives off alpha particles, this is a solid and thence a fine dust, ergo it collects in places and continues to emit before it decays to stable lead 206 22+ yrs later. Thus where you place your test puck matters hugely as does the topography and distribution of uranium ores underneath and around your property. Ideally you would have multiple detectors at multiple points, take multiple sets of readings and average them. In science a population size of '1' is not taken very seriously! Just saying.

1) Take up all the floorboards and remove a few inches of soil material to create space under the floor. This might involve add some additional height under the brick piers....maybe with breezeblocks or similar. I am a bit worried about the shallow footings though.

If you have no damp issues then if it ain't broke, don't fix it, leave your boards alone. Also with shallow footings you are weakening the structure and risking heave.

2) Add some additional air bricks to the opposite side of the house to promote more airflow. This is actully quite challenging with the 2ft thick walls and raised ground level outside. Any ideas? I would need to get a contractor as I don't feel confident doing that myself.

Reducing the ground level with a heavy structure and shallow footings would require a good surveryors advice as you can cause heave and slip. Best leave that a bit further down the options list.

3) Insulate between the joists using PIR on battens, otherwise the cold room is going to get much colder with the improved airflow. I think it will need to be PIR specifically because the joists are not very thick and PIR has the necessary U value to make a difference.

PIR will reduce moisture on the warm side but condense water vapour next to your timbers on the cold side, it might be a good idea, it might not, seems risky. Radon membranes are cheap! it's just a thick dpm sheet £1 sqm. To have it work you will need to remove floor, fit ply, fit membrane, then fit a floating floor on top as you cannot use penetrative fixings.

Have you considered a PIV system? Totally non invasive, will not affect damp, actually will improve damp levels, basically removes radon, moisture and other particles via a filtered positive pressure system whereby it pushes air out of the property and creates a small positive pressure which slows ingress of new particles. That and maybe additional air filters to remove particles before you can breathe them in. I would start with that.

Remember, unless you do all the work yourself or stand over them whilst they work, it's possible the membrane will not be installed 100% air tight. Anyway, those are my educated but inexperienced thoughts.

 

[Toby Newell]

If it were me I would:

100% no brainer do a second test, costs peanuts, peace of mind incalculable.
Look into a PIV system, will improve general air quality, improve damp levels and thus improve comfort levels (feeling of warmth) and reduce heating bills, (dry materials heat up faster and retain heat longer) then retest.
If this doesn't work as well as hoped then I would consider improving air brick situation.

 

[ncr703]

First of all, you have 'no reason to doubt' is reductive reasoning, qualitative and totally unscientific, how do you know your cheap detector was not faulty? Or that the lab had made a mistake? For something that affects possible cancer risk and whose remedy may cost thousands of pounds and a lot of stress, I would, very much, absolutely, do a second test and get it checked, not to do so seems like madness.

You make a very good point. I will do a second test with a different company.

I'll take a look into a PIV system. I have been a bit worried about these making a cold leaky house even colder which had caused me to discount them prematurely. To be clear there are no issues with damp in the house...partly due to good behaviour (no washing inside etc, good bathroom vents) but probably also because the house is bit drafty with a fire and oil boiler pulling fresh air (and radon!) into the house. Have you used PIVs and found the cold to be manageable?

 

[Toby Newell]

see edited post above again.

no, PIV should, in theory make your house warmer.

Latent heat of water = the greatest of any molecule in the universe, iirc, ergo heating it in air takes away a lot of energy, also, damp substrates conduct heat (wick to outside) much faster. Yes, you will push some warm air outside but this will possibly be matched or exceeded by the lower moisture in the air. PIV is good for general human and building health and is relatively inexpensive. Worth investigating.

 

[Toby Newell]

also, I would consider spending money much more efficiently insulating the upper floors / roof areas rather than below your feet, because. Physics. Heat rises, ergo more goes out the upper floors, roof and windows and hence the popularity of wearing woolly hats and tea cosies (looking at you Uncle Fred) on the head rather than the feet, or under the teapot.

And please don't take my scientific disdain for 'it will probably be ok' or, like many others, making assertions on the back of received wisdom or sample sizes of n=1 as being absolute, personally. Us scientifically minded on here only aim to help. Our incredulity beaten into us by our areas of study, such is the burden.

Nice thick T&G boards btw (I am a bit of a flooring guy when not slapping people with logic)

 

[Cubist]

Hello again,
Good to hear you've taken statistically meaningful readings over a sensible timeframe, I was concerned that a single and therefore potentially misleading 'point' reading had been taken. No detectors are absolutely accurate and the measures they produce should always be regarded with suspicion. If the system you used was from a reputable organisation and provided you with a full analysis of all the readings taken over the three month period then you can be reasonably confident it is broadly reliable. With more sophisticated kit it may be possible to determine the primary source of radon to be the ground immediately below the rooms but, the walls of your house will most likely have been constructed from stone gathered from the immediate area, and these may be the primary source of the radioactive isotopes responsible for the gas.

I think you already know that there is only one viable general strategy to significantly reduce the general radon level. That being to enhance the ventilation to dispel these harmful gases to outdoors as rapidly and effectively as possible. To do this though will require that, if the height of the floor is not to be raised, some of that soil must be removed to create the necessary airways needed route the gases toward the exits. In any event I would have been concerned about the condition of the submerged joists as, to my mind, this may promote rot and ultimately cause the floor to fail. In your shoes I would want to ensure some decent airflow around all aspects of the joists and the undersurface of any new floor-boards and supplemented with additional air bricks if at all possible. I would not however consider using any solution such as a gas impermeable membrane that traps the gas below the floor unless you are intending to use an active rather than a passive system to extract and remove that air Plastic sumps and a network of piping can be used for this purpose but there are space considerations associated with these.

I appreciate your desire to keep the rooms warm but suspect that any gain from insulation materials mounted below the floor would be marginal at best and could, as suggested by Mr Newell, promote other problems.

Best of luck.
Cubist

 

[Toby Newell]

Hello again,
Good to hear you've taken statistically meaningful readings over a sensible timeframe, I was concerned that a single and therefore potentially misleading 'point' reading had been taken. No detectors are absolutely accurate and the measures they produce should always be regarded with suspicion. If the system you used was from a reputable organisation and provided you with a full analysis of all the readings taken over the three month period then you can be reasonably confident it is broadly reliable. With more sophisticated kit it may be possible to determine the primary source of radon to be the ground immediately below the rooms but, the walls of your house will most likely have been constructed from stone gathered from the immediate area, and these may be the primary source of the radioactive isotopes responsible for the gas.

I think you already know that there is only one viable general strategy to significantly reduce the general radon level. That being to enhance the ventilation to dispel these harmful gases to outdoors as rapidly and effectively as possible. To do this though will require that, if the height of the floor is not to be raised, some of that soil must be removed to create the necessary airways needed route the gases toward the exits. In any event I would have been concerned about the condition of the submerged joists as, to my mind, this may promote rot and ultimately cause the floor to fail. In your shoes I would want to ensure some decent airflow around all aspects of the joists and the undersurface of any new floor-boards and supplemented with additional air bricks if at all possible. I would not however consider using any solution such as a gas impermeable membrane that traps the gas below the floor unless you are intending to use an active rather than a passive system to extract and remove that air Plastic sumps and a network of piping can be used for this purpose but there are space considerations associated with these.

I appreciate your desire to keep the rooms warm but suspect that any gain from insulation materials mounted below the floor would be marginal at best and could, as suggested by Mr Newell, promote other problems.

Best of luck.
Cubist

Statistically meaningful = unscientific, totally qualitative term it is one detector, in one position, with no corroboration. It may indeed be meaningful (that is a human qualitative construct) in indicating an elevated Radon level of a particular magnitude, but mathematically a sample size of n=1 with no check on whether that reading is erroneous would result in very high p value and so, mathematically and scientifically speaking, despite possibly being accurate, is nonetheless highly likely to be regarded as 'not statistically significant'. Just saying. That is why we have science, it is based on repeatable observations, not assumptions. As I understand it (maths is my weakest suit so someone please correct me if I am wrong!) When you conduct a second test your probability of error goes down by the error squared, ie if a test is 99.9% accurate that is a 1 in 1,000 error. If a second test returns the same result, the probability of both of them being erroneous would be 0.01 x 0.01 ie 0.0001. So you would gain 1000 x increase (three orders of magnitude) in accuracy for increasing the sample size by a factor of 2.

You will not find any of the hundreds of thousands of published peer-reviewed papers in any of the world's reputable scientific journals that present conclusive result data with a sample size of n=1. QED. Instead you will find hypotheses posed upon such that invite further investigation. Hearsay and assumption can indeed be good advice, but science just increases the weight of any such advice.

A reputable organisation is another human example of false assumptions and reductive reasoning. A 'reputable' organisation = what? have you read all the reviews? Do you know all the reviews are genuine? Even if it has a good reputation, what is the causal link between a well regarded company and the random probability of error? = zero. If there is no regulation how do you know the results are meaningful? Or their equipment calibrated accurately? Have you personally tested their equipment, or seen their certificate? There are over 5,000 people who contracted AIDS or gave it to their partners resulting in over 1,000 deaths because blood clotting factor was incorrectly screened for over a decade.

How many of those testing laboratories previously had a 'good reputation'? All of them were vetted and heavily regulated and tested by external agencies, as being critical to human life. I would say they were probably under a stronger regulatory framework than a radon testing company, yet 1,000 humans died. Again, just saying. You have to seperate reduction from deduction, the move to such was the biggest leap the Greeks made in critical thought and human thinking and is the basis of science as we see it today. Unfortunately, the way the human brain and psyche function are at odds with this. We are naturally pre-programmed to be susceptible to assumption and persuation which it is why people not trained in the sciences find it hard to understand and all of us are prone to it.

Double checking powerfully important and impactful issues for the cost of negligible money seems to me to be an easy decision.

As far as I am aware there are no regulatory frameworks for Radon testing in the UK. From the US data it appears measurement error is in the range of 5 to 25%. The number of randomly tested labs failing to meet this standard was 30 to 40% + (in two studies) Therefore we can conclude that an error, from one correctly placed charcoal adsorption puck could easily fall within the range of 25% + even if the testing procedure was carried out well and the substrate not contaminated. This implies that such a reading as the OP was given almost certainly indicates a higher than normal radon level, but that potentially it could be at least (maybe by a lot) 25% lower, or indeed higher. It is unlikely to be zero, or at normal levels, but may be at higher levels which would encourage greater urgency, or at lower levels which might de-prioritise the issue.

If it were me, I would absolutely get a second test (I would of placed multiple pucks in several areas) and I would also research and purchase a continuous monitor so that I could chart not only long term exposure, but possible cycles and how efficacious any mitigation efforts were. It is entirely possible that simple methods like increased cleaning with a HEPA vacuum, increased airflow by opening windows and simple small HEPA air purifiers would have a noticeable effect. Remember, the method of transport into the home is via the gas phase, but Radon has a half life of 3.8 days, (reduces by half every 3.8 days) so after a week, little (25%) of the original gas remains, instead what does is micro fine Lead (210 isotope) dust. For this reason I would keep the amount of soft furnishings to a minimum and certainly avoid carpets, which trap this radioactive lead dust and allow it to emit further alpha particles for decades (half life of Lead 210 = 22+ yrs) You might find non-intrusive, cheap and easy methods can bring down the radiation to an acceptable level without further control measures. Also concentrate on ground floor as radon, lead and polonium are all dense atoms and hence heavy, although I am unsure if that would affect the buoyancy of nanoparticle sized lead dust.

Cubist however brings up an incredibly important point that I overlooked. It might be helpful to try and find out if indeed the source of your radon is coming from the house structure itself or the ground underneath it as this might influence the most effective solution.

I am sure PIV would be helpful in both cases, but obviously a ground membrane is going to be less effective if the radon is coming from the walls.
If your stone walls are not emitting and it's the earth around then a membrane stops intrusion from below, a PIV stops intrusion from outside and better cleaning removes any remaining partially decayed emitting lead particulates.

I would also put in a water filtration system or certainly use a water filter jug at the minimum. Alpha radiation is stopped by the outer layers of skin, whilst Radon is both an alpha and beta (beta can partially enter skin) emitter, Lead 210 absorbs its own Beta particle (electron) and so a lot of the risk comes from ingested particles where alpha particles can cause unimpeded damage to chromosomes, the pathological risk being to the lungs. This is why any air filtration system can help.

Despite having worked on several hundred timber floors I have not seen that many that were directly laid to earth. (Although from your photos I am a little confused as I see boards laid on joist on brick piers) Most of those I have seen had severely decayed joist, but most of these were 200 - 400 yrs old. I am not an expert in damp but from what I know of wood, if there was an issue and your timbers are indeed from the 1970's that would indicate there is not a problem, as 50 years in contact with wet soil is more than enough time for severe rot to take hold.

It is true however, that as a precaution, the safest, if not the easiest course of action, would be to carefully lift the floor and place slate or other dpm between the bricks and the joist and treat the joist (or replace if stating to rot) at least the underside, with creosote or similar ( I use a 'blackjack' type bitumen flashing primer) this has nothing to do with the radon obviously! Also, if the brick piers are continuous, then making small gaps for the air to move would also help.

 

[Cubist]

On occasion it can feel quite flattering to see ones words quoted by another member during one of these discussions as frequently this feature is used to acknowledge a useful snippet and perhaps offer some small thanks. Most frequently however the tool is used merely to highlight a particular matter and to request additional information or explanation. It is also sometimes used to highlight particular passages that may be perceived to contain errors of fact or logic that deserve to be corrected for the benefit of the wider readership. Sadly, but happily very rarely, this capability is also occasionally exploited with dubious intent to ridicule the content and/or otherwise insult the author.

I try.... but I must admit, it can be very hard to resist taking some small malicious pleasure when efforts of the latter kind aimed at yours truly fall flat on their face.

Statistically meaningful = unscientific, totally qualitative term it is one detector, in one position, with no corroboration.....

NCR703 - was quite specific when he/she stated that the single radon gas meter used had been sited for 3 months. As I understand it, happy to be corrected if necessary, charcoal filter based meters are best employed for short term tests with a sampling duration of up to 7-8 days. Those designed for use over longer periods of up to 30 days typically use photodiode technologies to gather between 3,500-4,500 individual readings to form the overall sample population for later analysis to determine the Average, Mean, Range, Distribution Curve and Skew of all those readings.

That said, it should be noted that any inherent technical fault within that one device may influence and therefore bias these final measures either positively or negatively and as a consequence the users are entirely dependent on the efficacy of the device manufacturers QA & QC processes to weed out such defects.

A reputable organisation is another human example of false assumptions and reductive reasoning. A 'reputable' organisation = ...

How many of those testing laboratories previously had a 'good reputation'? All of them were vetted and heavily regulated and tested by external agencies, as being critical to human life. I would say they were probably under a stronger regulatory framework than a radon testing company, yet 1,000 humans died. Again, just saying......

I'm not entirely sure what the point and relevance of these rather emotive statements is. Sadly its a fact of life that we live in a 'Buyer Beware' world in which it is always wise to check the credentials and claimed achievements of any particular product or service we may be considering for purchase or use. Unfortunately, and irrespective of whether the decision is based on the individuals reductive or deductive critical reasoning skills, in the final analysis there is no choice, a leap of trust, and to some extent faith, is unavoidable in every transaction irrespective of its nature.

Double checking powerfully important and impactful issues for the cost of negligible money seems to me to be an easy decision.

Well yes. If you have reason to believe that the equipment or service employed has produced erroneous results. But then, in this particular example, you may find that the second examination produces radon measures that are;

1. broadly similar
2. marginally or considerably greater
3. or marginally or considerably smaller

So, with whatever critical reasoning system you may employ, what action. should you take? Option 1 is obviously clear and confirms either a good or bad result, while 2 and 3 could be intepreted to simply mean that your old, or new, meter was/is wrong! So then what?

The right answer is hopefully obvious to anyone. An assumption must be made based on your understanding of the potential for harm to yourself and your family - given negative results in the first round I hope most people would act promptly!

As far as I am aware there are no regulatory frameworks for Radon testing in the UK. From the US data it appears measurement error is in the range of 5 to 25%. ,,,,

I am thoroughly ignorant of any of the studies referred to above. Nor am I aware of any relevant UK agency, other than perhaps UKHSA, that might enforce relevant regulations. Consequently, I am not in a position, nor, frankly, am I inclined to, verify the provenance of the statistical evidence presented above concerning the possible performance of charcoal filter pucks. However, the authors resort to 'unscientific' measures to support his case is nevertheless mildly amusing.

If it were me, I would absolutely get a second test (I would of placed multiple pucks in several areas) and I would also research and purchase a continuous monitor ...

Setting aside the first sentence and the rather blinding blizzard of science speak, theres some useful advice here that may be worth acting upon. In particular that concerning continuous monitoring if ones home has a history of high radon readings. One of the little known and largely undiscussed issues is that radon gas levels in a building can fluctuate and spike, sometimes dramatically, with even relatively minor changes in the local environment such as prevailing wind direction. I do wonder though how many people might balk at the adoption of a spartan, minimalist and austere lifestyle.

Cubist however brings up an incredibly important point that I overlooked. It might be helpful to try and find out if indeed the source of your radon is coming from the house structure itself or the ground underneath it as this might influence the most effective solution.

And here perhaps we have what I suspect is the reason for the efforts to rubbish some of my earlier words. I can only think that it must have been terribly galling for the author to have to acknowledge that I had highlighted this one irrefutable fact that he had overlooked in his own contributions.

Really, is that it?

 

[Toby Newell]

I think a large pot of tea and a nice lie down is in order.

My point was that cheap charcoal pucks are very sensitive to placement, radon and lead dust are much heavier than air and so the puck may receive a much higher dose than a human would.

Pucks also take one reading, the cumulative number of adsorbed particles, their accuracy is up to 75% and thus a dangerously high reading might not be as bad as it seems, or a lot worse. Radon labs are not regulated so you are just guessing they didn't make an error in the titration or gas chromatography or whatever method they use to estimate particle number.

Pucks are placed for 3 to 12 months for a more accurate reading, but they are cheap and not the gold standard.

Even then, this is a number relating to the amount of particles adsorbed in that particular few centimetres.

My point was that for something so potentially worrying a second test, at least, possibly in another part of the room, might be prudent.

I aim to provide as much helpful, factual information as I can.

I was, again, nothing personal, simply pointing out that one reading may or may not be accurate but not statistically significant as you implied.

Your post seemed to dispute mine (no offence taken btw) in that one reading from a cheap, low efficacy method, with results from one, unregulated lab of whose test equipment, calibration and methods you know not of, is absolutely fine. You attributed this confidence to the fact that the company was 'reputable' (without providing any proof of reputation)

I was giving an example of where a much more tightly regulated lab (human blood screening) had made catastrophic errors that lead to over 1,000 deaths and 5,000 cases of increased morbidity and that, presumably, some or all of these labs had previously had a 'good reputation'.

If you are going to enter the fray of discourse, by suggesting my advice is irrelevant and then getting upset when I simply back that advice up with logic and facts, well, don't enter the fray.

You only have yourself to blame.

For my part I am sorry you have taken offence to science and facts, but there was no insulting, only that which you assumed.

I myself am not in the least bit upset or insulted that you challenged my original advice or sought fit to write this diatribe.

But if you are going to counter someones advice, maybe you shouldn't be upset when they defend it.

 

[Toby Newell]

Final word.

I think it is always important to remember to view an argument from the other persons viewpoint.

You made an illogical and unscientific affirmative statement that spiked Matt, who has completed a thesis on wood boring insects, corrected you on. Yes, quite heavily, I am sure he didn't take your assertion personally, only an affront to science!

Same here, I studied materials engineering which included fundamental science including quantum theory, you are free to make any assertions you like, but when people schooled in the sciences see an obviously unscientific error, it can spike us.

We defend not so much ourselves, but rather the scientific method.

This is an advice forum, most advice is received wisdom, some of it from direct experience. Those of us who have studied and continue to study, try to put forth facts, and dispel common misconceptions and myths in the hope that this information might be useful.

I would agree, any clumsy language or other condescending verbosity is uncalled for, but a light flaming is part of the reward for our efforts. (you may be unaware of the hundreds of hours of research and study I have undertaken since 2006 in order to better serve this forum and give accurate advice)

Having said that, despite our failings as perfect humans, and our propensity to be a bit cheeky, any offence or insult is merely collateral damage on the path to the elucidation of the facts, as best we know them.

That is as close as you are going to get to an apology, so enjoy it with your cup of tea.

 

[Toby Newell]

Getting back to the OP's situation.

I would be very interested to learn more about the pathway to adsorbtion by humans, of radio nucleotides.

I am aware most of the pathogenicity is via ingestion through the lungs or digestive tract.

I wonder if any research has been done regarding fluid dynamics as radon is a very heavy gas and decays to nano particle sized lead 210 dust, which again would function essentially, as a heavy gas.

This is key to mitigation and why basements are the most dangerous places.

Fluid dynamics are chaotic and require serious compute power, there seems to be quite a lot of Radon concern in the US and the US does a great amount of research, I wonder if anyone has looked into it in that great detail. That's why I was thinking fans might be good.

Might be worth checking out the NCBI (NIH) I have personally read hundreds of scientific papers on there, if there is not a full publish there is often a summary which can be easier to digest! I think it's one of the most marvellous resources on the internet.

 

[ncr703]

Alright, that's lovely, thank you.

Moving on, I have committed. Much to my wife's delight I have taken up the whole floor (pic!). It's not as bad as I expected, with only the areas that were "improved" in the 1970s having poor, lazy workmanship (appalling, actually).

I still intend to remove a small amount of loose soil for additional air gap depth where it cannot contribute to slip and heave, and to replace some joists where they have rotted from touching the soil (pic!) , or even been encased in concrete . Thankfully 80% of the joists are in good condition.
In the bay window I'm planning to remove the radiator and install 2 periscope vents to vent the subfloor outside above the raised outdoor ground level. There are 2 existing vents on the French door side, so I'll then have cross-room air flow to vent the subfloor properly and vent the radon.

Here's the bit I'm not sure about from a timber longevity point if view;
I am considering after refitting the floorboards installing a radon barrier, which is vapour impermeable ,on top, then the chosen underlay and flooring on top of the barrier. My thinking is that the subfloor ventilation should prevent damage to the timbers, which I will leave uninsulated, and that this barrier will help to get the radon out rather than it being drawn in over the whole floor area via the chimney effect. I won't be able to achieve a 100% seal, but I reason that even a 90% seal, in combination with subfloor ventilation, will contribute to a significant lowering of the radon levels. The radon literature I have waded through suggests that this may help (albeit only slightly - the ventilation is the major effect) with radon but it does not discuss the timber longevity.
Is this idea likely to cause rot issues, or is this silly for any other reasons?

 

[Toby Newell]

First of all, well done. This all seems sensible.

Could you not fit the barrier underneath the joist?

Remove the stones, compact and level, put fine sand, place plastic barrier, then piers (use engineering bricks with rubber spacer pads underneath to avoid puncture) then joist, fit floor and seal gaps.

I agree, increasing ventilation and not reducing airflow with insulation.

As far as I understand it radon will be all around, you don't want it collecting, so air movement is key, chimney effect is a positive, not negative, there is more concentrated radon underneath your floor as opposed to more dilute radon in the surtounding air, thus you are reducing the radon concentration in your home. Also radon is emitted from rocks underneath, so you are stopping that too.

You can fill the floorboard gaps with glued wood slivers (buy from KHR) this would provide a gas barrier but allow moisture to wick away through the top surface. (I would finish with Bona Hardwax Oil for breathable top coat if wanting natural wood finish)

Also, if you attach boards using penetrative fixings this will puncture the barrier, having the barrier underneath the piers, not so much.

These are just opinions, but I feel that trapping noisture underneath the floor might not be a good idea.

In any case I might treat the joist with preservative and fit dpm between the piers and joist, I use bitumen flashing tape + bitumen primer. (I figure less likely to split and provides slight cushioning for more secure setting)

Don't tell me about all the botches! Closet full of t shirts here...