I recently installed another radon remediation system -- sub-slab depressurization -- in a house I plan to sell in the near future. The house was built in 1991, so there was a layer of pea rock gravel under the basement floor, but no vapor barrier. The soil is very gravelly, so the basement stays fairly dry anyway. The radon level measured in the range 5.6 to 5.9 pCi/L before the radon reduction system was installed. Since then, with the radon fan operating continuously, the level has dropped to the range of 1.7 to 2.6 depending on the measurement location. The section of the basement finished off with a ceramic floor has the lowest radon measurement, while areas will unsealed concrete floor, the highest. This was a DIY installation utilizing 40 feet of 4" PVC piping through the roof and fan in the attic. The slab area is about 2400 sq. ft. including the attached garage at the same level. The fan produces suction of 1.7" water column drawing 80 watts. The total material cost was about $300.

It may be an obvious point, but I'll make it anyway. The amount of electric power needed to vent enough air from under the slab is likely to be considerably more for a radon reduction system installed as an after thought than for one that is planned at the time of building construction, that is, for example, by laying perforated piping under the slab around the perimeter of the building inside the footing before the floor is poured. If that had been done, a low wattage fan would have been sufficient, and been more effective in reducing the radon level. I base that on my having done that for a similar sized slab in similar soil that produced slightly higher levels of radon gas, but using only a 14 watt fan to achieve similar results. The cost of laying the extra perforated pipe (our local building code only requires a short length of pipe in the sub-slab gravel) will be paid back in lower electric bills in a relatively short time. At $0.11/KWH, I estimate a savings of about $50 - $60/year. Of course, if radon accumulation had turned out not to be a problem, the extra money would have been spent needlessly. Amazingly, my next door neighbor has no problem with radon gas.

If radon molecular weight is 226 it is a lot heavier than air, right?

So, it would puddle, or build up from the ground. If any gets into the livingspace, would ERV's not completely remove it unless the air movement volume is high?

Posted By Gary Olsen on 18 Nov 2012 09:38 AM
If radon molecular weight is 226 it is a lot heavier than air, right?

So, it would puddle, or build up from the ground. If any gets into the livingspace, would ERV's not completely remove it unless the air movement volume is high?

Maybe more effectively, it would be good to have at least one stale air inlet to the HRV/ERV in the basement or crawlspace if there is one.  If there is no basement or crawl space, then having at least one inlet close to the floor would be effective.  (The molecular weight of air is about 29, so yes, radon is much heavier.)

I have a conditioned crawl space, and both inlets to the HRV are in the crawl space to draw air from the house through the crawl space to the exhaust.  There are four passive vents from the house to the crawl space.  There are separate exhaust systems for the kitchen and bathrooms.   

Posted By Clark on 16 Nov 2012 03:56 PM
...snip...
 The fan produces suction of 1.7" water column drawing 80 watts. The total material cost was about $300.

It may be an obvious point, but I'll make it anyway. The amount of electric power needed to vent enough air from under the slab is likely to be considerably more for a radon reduction system installed as an after thought than for one that is planned at the time of building construction, that is, for example, by laying perforated piping under the slab around the perimeter of the building inside the footing before the floor is poured. If that had been done, a low wattage fan would have been sufficient, and been more effective in reducing the radon level. I base that on my having done that for a similar sized slab in similar soil that produced slightly higher levels of radon gas, but using only a 14 watt fan to achieve similar results. The cost of laying the extra perforated pipe (our local building code only requires a short length of pipe in the sub-slab gravel) will be paid back in lower electric bills in a relatively short time. At $0.11/KWH, I estimate a savings of about $50 - $60/year. Of course, if radon accumulation had turned out not to be a problem, the extra money would have been spent needlessly. Amazingly, my next door neighbor has no problem with radon gas.

I agree.  My house was constructed with two collection pipes under the conditioned crawl space running parallel to the longer axis of the house.  It was constructed as a passive system, but unfortunately, the 4" collection system was reduced to 2" piping to duct it through the house, and the measured radon level was about 8.8 pCi/L, higher than the recommended max of 4.0.  A small 14 W fan in each leg reduced it to 1.2 pCi/L.    

Lee, instead of two collections pipes, I was thinking of using one as an air intake, and the the other as the collector.  So that you would be sweeping the volume out with fresh air.  that should allow a smaller fan as you wouldn't be drawing a vacuum.  Does this make sense?

You need the vacuum to assure that you don't get leakage into the house.

Posted By LarryT on 21 Nov 2012 10:26 PM
Lee, instead of two collections pipes, I was thinking of using one as an air intake, and the the other as the collector.  So that you would be sweeping the volume out with fresh air.  that should allow a smaller fan as you wouldn't be drawing a vacuum.  Does this make sense?

Larry-

I would agree with jonr that the safest approach would be to have a differential pressure between the basement, crawl space, or slab and the space below that would tend to draw gases from the house to the radon remediation system.  If you were able to get away with a low power fan, say 14 W to 20 W, then the power draw is quite low. 

If you went with two pipes used as you suggest, then you would need to lay them along the bottom edge of the foundation to sweep the whole volume under the basement/crawl space/slab. 

Lee,  laying them at the foundation under slab is what I was thinking.  The main purpose would be to sweep radon out immediately as it eminates from the soil - at its source point so to speak.  That would eliminate it ever getting further.

I have a few questions. First, should the radon barrier extend from on top of the ground level(under the house floor) then a)go beneath the foundation footer, b)wrap over the top of the foundation wall, or c)just butt up to the foundation wall? Second, I like the idea of stale house air going into the air space beneath the floor on it's way to the HRV, but if the radon barrier is well done, would it need to go beneath the radon barrier? Does this approach lessen the efficiency of the HRV? Third, if the floor is SIP's on gravel(no slab), where would the HRV air flow? Thanks, Gary

I think the IRC Appendix F specifies adequate new construction radon resistance provisions. It's been adopted by many states or local jurisdictions to address radon gas infiltration via barrier installation and sub-slab depressurization. Passive depressurization may be all that's needed to keep radon levels within EPA guidelines. If not, as was my experience, adding a low wattage fan did the trick. I once ran across a radon barrier design out of Sweden, I think it was, in which the poly membrane extended under the foundation walls making it difficult for radon to leak into the house at the floor-wall intersection. I would have used this method if I had known about it at the time.

Posted By LarryT on 23 Nov 2012 03:46 PM
Lee,  laying them at the foundation under slab is what I was thinking.  The main purpose would be to sweep radon out immediately as it eminates from the soil - at its source point so to speak.  That would eliminate it ever getting further.

Larry-

As pointed out by Clark, the International Residential Code (IRC) Appendix F, "Radon Control Methods," (http://www.wpb-radon.com/pdf/IRC%20Appendix%20F.pdf) requires depressurization of the sub-slab or sub-membrane area. Rather than inventing your own method, it would be best to follow that code.

Lee,

I guess that is what I'll do.  Thanks for the link.  I had been looking for information on line before and couldn't find it.  This gives me several options.

I'll end up using a "drain tile" method as the area is large enough I want more exposure than what a single 3" tee under one end would give me. 

Larry

 

Note that the better you seal the floor, the less air flow you have and the less air flow, the less need for piping to distribute the vacuum. Not to mention less electricity for a fan and less heat loss.