I have also done over 4000 mitigations and have had a handful of failures including a few that I never solved. We have always done pressure field extension testing using a Minneapolis micromanometer and, in one case, measured -2 pa wrt the basement at the furthest test hole and didn't change the radon level when the fan was running. I totally agree that pressure field extension testing should be done with at least one test hole where feasible, but it is not a guarantee of success. And there are complicating factors including interior and/or exterior drain tile with drain to daylight, highly finished basements, karst geology, etc that make PFE testing problematical.

Where was your testing done?

You mentioned that the fan pressure for the RP265 was .5". That is really low and indicates a very high flow.Yet you said that the slab was 14" to 22" thick and you measured minimal pressure drop across the slab. This indicates to me that most of the air traveling through the RP265 must be coming from the basement, and the initial reduction in radon could have been due to dilution from negative pressure pulling air into the basement either from the living space above or through the foundation. Did you do any measurements of the pressure in the basement wrt the exterior or first floor with the RP265 on and off? The HRV/ERV will probably work, but you might want to monitor the pressure changes in the basement when configuring the intake and exhaust flows.

Sump sealing is not straightforward. Sumps can be standard crocks with pedestal or submersible pumps. The can have two sump pumps installed or elaborate water backup systems. They can be ceramic crocks with raised, rounded tops. They can be precast concrete 11" square pits. They can be shallow holes in a dirt floor. They can be plastic buckets set into the concrete slab projecting 2" above the slab. and on and on. The principle for sealing is simple. The practice can get complicated.

I agree with everything you are saying. Here's the fundamental problem. This is a mandate from the Department of Energy to Weatherization agencies. Active mitigation measures are not approved, even when a simple SSD would cost less in labor and materials than sealing a rubble stone wall. It's government bureaucracy at its worst. But the whole issue has raised a larger and more interesting question. For years, in the weatherization industry there has been a concern to establish best practices, which has culminated in a project to create Standard Work Specifications. The SWS's are publicly available (https://sws.nrel.gov/). They were created mostly with input from the industry and technical experts. Nothing like this exists for the radon mitigation industry. It's a project that might be worth thinking about for the limited number of procedures we use in our work.

You captured the problems I'm dealing with exactly:
"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" and any barrier of any kind I install would have to have the capacity to "drain any accumulated water as you can't simply let it pool at the bottom of the wall with no where to go", and I can't figure out a way to do this inexpensively and effectively. As for the budget issue, I have been asked by low-income weatherization agencies in two states to write passive radon mitigation procedures to include:
1. Floor crack sealing
2. Floor and wall penetration sealing
3. Sump sealing
4. Crawlspace sealing
5. Rubble stone wall sealing
And budget issues are huge because it is in the context of low-income weatherization work.

Thanks for responding. I did look at Lstiburek's article. What struck me was the detail that preserved a drainage plain between the rubble stone wall and the spray polyurethane foam. The membrane creating the drainage plain extended below the slab into a french drain water collection system. At no point was spray foam directly applied to the wall. For radon mitigation in an existing house, the foam insulation is not required, but sealing the membrane to create a sufficient radon barrier and preserving the required drainage plain would be a major project. See Bob Wood's comments.

It's interesting to think about the possibility that sub-slab depressurization is reaching under the 18" rubble stone foundation. Would be an interesting experiment to inject tracer gas on the outside of the foundation and see if it shows up in the radon pipe. Even more interesting would be to use a standard wall with a footer as a control for the experiment.

Useful and important information. Thanks

I guess I wasn't clear in my description of the problem. We've also always used 1/4" Lexan for sump covers. We've also been able to buy 4'x8' sheets locally and cut them into 2'x4' pieces and we've used all the techniques for sealing that you have all described depending on the surface we need to seal down to. My concern is with the rare, but problematic, issue where the "sump hole" is a 6" to 1' dug out depression in the floor with a pedestal sump pump just sitting in the hole. I suspect it's there not so much for water table problems but for dealing with surface water and I don't want to eliminate it.

You only have 28 hours of data for a 47 hr test based on your stated start and end dates and times. The data is also not consistent with a claim that the monitor was never initially turned on since there's 3 hourly data points before the power failure unless it was running on battery power for three hours and then the batteries died. It is fishy to say the least. You need to redo the test.

Besides a cold slab, a likely problem will be condensation on the surface of the interior pipes during cold weather. Depending on the relative humidity in the basement, it could be extensive, and would require installing pipe insulation on all interior pipes, especially horizontal runs. The other potential problem is debris, such as leaves, falling into the vent unless you have a vent cap.

Thanks for the responses. They all either confirmed my experiences or added to my knowledge.

Randy, you have more data than I have, but it conforms with my more limited experience. Sealing alone does not do much to reduce radon levels.

John and David, I agree with you about the beneficial effect of ASD on basement humidity. We have seen this reported over and over from customers. It would be interesting to see a study comparing the costs of ASD as a dehumidifying strategy versus dehumidifiers. Unfortunately, for the low-income weatherization industry, capital costs and budget limitations rule.

Gary, totally agree that " fat chance for reducing 8 pCi/L to > 4 pCi/L with passive efforts." I'm glad you mentioned the importance of stack effect.. The good news from the Wx front is that attic air sealing is an absolute priority in weatherization, and, as far as I know, is always done.I also know that basement duct sealing is done routinely. If return duct leaks predominate over supply duct leaks, than duct sealing should reduce basement radon levels (we've actually done return duct sealing in our private sector radon work). However, the national IAQ study, which measured radon levels before and after Wx work couldn't definitively conclude that Wx, which always included attic air sealing, significantly reduces basement radon levels. Part of this may be due to the fact that the buildings were also tightened so that natural ventilation was reduced.

There is some interesting research from Paul Francisco of the University of Illinois that increasing whole house ventilation, even using exhaust only ventilation (e.g. bath fans on timers), tends to reduce radon in the living spaces of homes slated for weatherization services.

It's all very complicated, but I hate to see Wx dollars wasted on measures that don't work.

Thanks.

Dick Kornbluth

I would certainly be interested in any studies that investigated the performance of passive measures only in existing buildings. If anyone has a link to any studies or documents from the studies, please let me know. I only have my personal experience to go by, which is limited, although not encouraging wrt passive measure effectiveness in reducing radon in existing buildings.

Thanks for the comments. However the context for my post was not new construction. It was Weatherization, which is exclusively existing houses, and my comment on my personal experiences was also in the context of existing houses.

(Apparently my email address in my original post didn't translate too clearly. I hope this is better:
rakornbl @ twcny . rr . com)

The other problem with fans in side attics is that they don't meet the ASTM 2121 requirements that radon fans must be installed "above the conditioned...spaces".

ASTM 2121: "7.3.3.2 Radon fans used in ASD radon mitigation systems shall be installed either outside the building or inside the building, outside of occupiable space, and above the conditioned (heated/cooled) spaces of a building."

It is interesting to note that attic spaces brought into the "conditioned" space when roof decks are insulated may not be occupiable and are certainly not intentionally heated or cooled. They are technically not conditioned spaces, but are inside the building envelope. This does raise interesting questions about vented vs unvented attic spaces in general. In cold climates in the winter time, stack effect produces a positive pressure at the top of the conditioned space which would prevent radon entry from the attic into the living space. However, in cold climates in the summer or in cooling climates, stack effect is reversed and the pressure is positive from the attic towards the living space. What would that mean if the attic was not vented and there was a leak in a radon fan under these conditions?

In Central New York, a Zone 1 area, very few builders are employing RRNC techniques. Those that do will install a single passive 3" pipe as the only measure, even in houses greater than 3000 sf. Often, the pipe will be run through an exterior wall and will enter the attic so close to the soffit that installing a fan in the attic will be impossible. Suction pits are never created. The pipes are just jammed into the stone. We have even encountered passive pipes buried in the concrete slab. Builders in our area routinely create floating slabs with open perimeter drains and open sump crocks along with the passive radon pipe. The result of all this is that we often have to cap the passive pipe at the top and start from scratch when installing radon mitigation systems. Clearly what is needed in New York is a change to the building code that mandates proper RRNC construction techniques and that is extremely unlikely to ever happen in an already unregulated state where radon testing is regulated but mitigation is not.

We have used the masking tape technique. Sometimes we'll have to do a little touchup at the joints after the pipe is re-installed. And, yes, tall vent pipes can be challenging.

I agree with Henri. My only caution is to be careful about painting the pipe sections before assembling the pipe. The thickness of the paint will interfere with attaching the pipe to fittings. We learned this the hard way!

We have used a Pylon AB5 radiation monitor. It's a research level instrument and very versatile. It can be used for sniffing, short-term and long-term radon measurements. I have seen several recently listed on Ebay for $4-500. There may be additional costs for scintillation cells which can be purchased from http://radoncorp.com/testing/pylon-monitors.php in the United States.