Thread: radon mitigation

Consider a house with sloped lot. The lot is sloped front to rear. At the front, the grade is just below the 1st floor level. The grade slopes to the rear where there's a walk out sliding door on the back of the house.

The front 1/2 is on a crawl space that is closer to grade. The rear half is a basement with a concrete salb. The crawl space floor on the front half is 4-5 feet above the level of the slab of the rear 1/2.

When mitigating radon in a house like this, would you do the crawl first, or the the sub slab first? I understand its possible that both might be needed but if you were going to do one first, which would be more effective?

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I would do the basement first.
If the crawlspace is vented, the air exchange will help reduce radon build-up. In the basement, the radon is already in the house.

Basement first, but most likely both will need to be done. What was the pCi/L reading?

The house in question is a family members. We've had one of my 1027's over there for extended periods in the past. Highs in the basement were in the 19's for short term averages. 1st floor erratic depending on conditions such as open or closed house conditions. The reading spike significantly during bad weather, mainly rain.

We're running a long term test with an alpha track now.

Originally Posted by John Dirks Jr

The house in question is a family members. We've had one of my 1027's over there for extended periods in the past. Highs in the basement were in the 19's for short term averages. 1st floor erratic depending on conditions such as open or closed house conditions. The reading spike significantly during bad weather, mainly rain.

That is normal during bad weather, rain, snow , etc....

We're running a long term test with an alpha track now.

That will give you the best reading.

Is the crawlspace concrete, gravel or dirt? Is the basement walls poured concrete of block walls? Do you have sump pit anywhere? + more questions.

Normally a mitigator will treat both area's (required here in IL) unless you can justify why it is not done. Justification is a radon diagnostic test which can be with a short term radon tests (both need to be < 4.0 pCI/L come one in basement and one above the crawl) and pressure extension readings with a micro manometer. In every proposal we require our design to be followed to warranty our service. Out designs treat all areas.
If a customer insists to treat only one area at a time the price goes up because we are wasting more time ... Time is money..

Just my 2 cents

And it really may not be that hard to do both. It all depends if you can put the basement radon pipe close to the crawlspace, all you would then need is some extra pipe and a 'Y'.

Darren,

If the basement and crawl have common air space you will need to do both.

If they are totally separate you can do the area that you took the reading in first, but I suspect you'll need to do both areas. Besides, you would want to get the long term average below 2.0 as recommended by EPA.

Originally Posted by Paul Ybarra

Is the crawlspace concrete, gravel or dirt? Is the basement walls poured concrete of block walls? Do you have sump pit anywhere? + more questions.

Normally a mitigator will treat both area's (required here in IL) unless you can justify why it is not done. Justification is a radon diagnostic test which can be with a short term radon tests (both need to be < 4.0 pCI/L come one in basement and one above the crawl) and pressure extension readings with a micro manometer. In every proposal we require our design to be followed to warranty our service. Out designs treat all areas.
If a customer insists to treat only one area at a time the price goes up because we are wasting more time ... Time is money..

Just my 2 cents

Crawl is dirt with a plastic barrier that has openings that need sealing. Poured concrete basement walls. No sump pit.

John,

Are there ducts running through the crawl?
Sealing all the duct joints in a crawlspace with the probability of radon is a requirement here in NJ.

Originally Posted by Darren Miller

Are there ducts running through the crawl?
Sealing all the duct joints in a crawlspace with the probability of radon is a requirement here in NJ.

Are you also required to seal duct joints in a basement with a probability of radon?

Originally Posted by Darren Miller

John,

Are there ducts running through the crawl?
Sealing all the duct joints in a crawlspace with the probability of radon is a requirement here in NJ.

Yeah, ducts are in the crawl. At the following page from my site, that's me checking out one of them in the very crawl that we're discussing.

Maryland-Home-Inspectors-Licensed-Annapolis-Baltimore-Anne Arundel-Prince Georges

Originally Posted by Bruce Breedlove

Are you also required to seal duct joints in a basement with a probability of radon?

No. Here's what it says:

9) Any ductwork that is routed through a crawlspace or beneath a slab shall be properly taped or sealed.

John,
Since the crawl space is dirt with plastic is it ventilated? If so, what type?
You say it has opening that need sealing. Are they partial sealed now?
What were the readings in the crawl space?

Originally Posted by John Dirks Jr

Crawl is dirt with a plastic barrier that has openings that need sealing. Poured concrete basement walls. No sump pit.

John,
I installed radon mitigation systems for many years (back in the 90's). Based upon experience, the crawlspace is the source.

We'd seal it up with thick mil plastic and create a sub-membrane depressurization system. Liquid Nails on the foundation perimeter and at seams and penetrations. We credit that work towards a full system if needed after testing just that crawlspace seal. Just sealing the crawlspace will affect the Rn levels tremendously, but will not likely get it down to 'safe.' So before sealing the crawlspace over, we'd install branched perforated PVC, and pipe a penetration up through the plastic and cap it for future. Now if you stick a fan on that crawlspace system, that would probably take care of the entire house. The low pressure on the crawl will draw a ton.

A sub-membrane depressurization system for a crawlspace is the most effective method.

But just to make it legit, pop a hole in the basement floor too. Connect that basement point to the crawlspace system and blow it out.

Crawlspaces are actually an ideal thing for mitigators, because it's typical THE source. We typically love hitting the crawlspace first, because it's highly effective and working the crawlspace is cosmetically appealing to the homeowner (who was likely trying to sell the property and keep things pretty.)

For inspecting radon mitigation systems, I wrote a Standards of Practice for Inspecting Radon Mitigation Systems International Standards of Practice for Inspecting Commercial Properties - InterNACHI

Hope that helps.

I would do the slab. If that takes care of it fine if not I would install a Temp Vent fan in the crawl space. If that didn't do it I would then place the barrier in the crawl and hook into the system.

I do radon testing in Chicago and suburbs and I cannot remember ever performing a post mitigation radon test on a house where the both basement and crawl were not mitigated as a unit. Can't imagine there are any real savings by choosing to mitigate one foundation type over another.

John,

I agree with Ben and this can be a "do it yourself" project for the family member. I would add some PVC drain pipes (depending on size) under the vapor barrier, seal the barrier seams and attach to foundation walls. Add your fan system and then re-test. Most likely this will bring the readings under 4.0


//Rick


Lopez Home Inspections; San Juan Island Home Inspections By Pacific Crest Inspections
Orcas Village and East Sound Home Inspections; Orcas Island Home Inspections By Pacific Crest Inspections

Since the possibility is that both will be needed and the crawl portion is more DIY friendly, we'll have the contractor install a sub slab de-pressurization for the basement. He'll be installing a capped T in the up pipe so we can tie in a sub membrane from the crawl if needed.

Thanks everyone for your input. I'll keep you posted on the proceedings.