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Radon mitigation....in a mostly underground home.

bgaidan

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Anyone ever dealt with it? I'm familiar with traditional radon venting (sump hole in a basement slab/walls and suck the gas outside.), but this is a bit of a weird one...

I'm under contract to buy a property with two houses on it. One is old - the foundation dates back to 1810 and the house was "built" in 1989. The other is basically a smaller version of the main house that was built for the mother-in-law. Both are built in to hill sides where 3 walls are mostly underground. They're basically just big basements.

I had radon tests done as part of the inspection and got the results back last night.

Bigger house is 3,600sf and the foundation is made of ~1,5' thick stacked/mortared stone. Levels were:
2.9 pCi/L min, 10 max, 6.7 average.

Smaller house was built about 10 years ago, typical CMU block foundation walls, waterproofed in the underground parts. Levels were:
1.1pCi/L min, 8.7 max, 4.9 average



From what I'm reading, anything over 2.7 should be mitigated. Levels around 5 are the lung cancer risk equivalent to smoking a half pack a day. :eek:


Like I said, I'm familiar with mitigation in normal house construction - either basement or crawl space - where you just suck the gas outside and keep it from getting in the living area, but I'm not sure how they accomplish that when the living area is effectively entirely comprised of a basement.


Any experts?
 
Tear out the floor, run perforated tube in gravel, cover with plastic, vent in solid PVC, pour new floor. Add radon fan in-line with vent.


At least that's how they do all the new houses. It's a big enough deal here that they just always install the tubing and plastic below slab and run the vent. If a test comes back high they cut the pipe in the attic and add the fancy little fan. I think the fan is the stupid expensive part.
 
Tear out the floor, run perforated tube in gravel, cover with plastic, vent in solid PVC, pour new floor. Add radon fan in-line with vent.


At least that's how they do all the new houses. It's a big enough deal here that they just always install the tubing and plastic below slab and run the vent. If a test comes back high they cut the pipe in the attic and add the fancy little fan. I think the fan is the stupid expensive part.

Yeah....3,600 sf + 1,600 sf worth of slab replacement.
 
Figure about 3k per house if you can find someone to touch the dam thing. Does your house have dirt on the roof or just in set into the hill?

You remember my house that was into the hill with grass covering the roof. Yea I got lucky that I found someone that had never installed one in a underground home otherwise he was going to pass. The system was installed by cutting a hole thru the concrete slab and cutting the plastic sheet covering the gravel to gain access to the gravel. Next a 4in PVC pipe was slid into the hole and the pipped up thru a side wall then vertical thru the grass and dirt. Thought about going thru roof but was suggested it could be 18inches thick with rebar. Getting the pipe from the wall to above the grass was absolute fucking hell. I had 40inches of dirt on top of the roof which took awhile to dig thru especially since there was an old roof membrane located 20inches down. By some miracle we dug in the right spot. Once the piping was complete he seal the joint areas and installed a fan on the roof. The system would then pull air flow from under the slab and out thru pipe. If I wasnt on site to help dig hole he was going to leave after he had already drilled a few holes in the side wall.

By the way I had ground radar down to see where the footers were in the house for 600. Yea that got fucked up since he hit one along with the wiring for the water heater. According to survey that area was clear.
 
Figure about 3k per house if you can find someone to touch the dam thing. Does your house have dirt on the roof or just in set into the hill?

You remember my house that was into the hill with grass covering the roof. Yea I got lucky that I found someone that had never installed one in a underground home otherwise he was going to pass. The system was installed by cutting a hole thru the concrete slab and cutting the plastic sheet covering the gravel to gain access to the gravel. Next a 4in PVC pipe was slid into the hole and the pipped up thru a side wall then vertical thru the grass and dirt. Thought about going thru roof but was suggested it could be 18inches thick with rebar. Getting the pipe from the wall to above the grass was absolute fucking hell. I had 40inches of dirt on top of the roof which took awhile to dig thru especially since there was an old roof membrane located 20inches down. By some miracle we dug in the right spot. Once the piping was complete he seal the joint areas and installed a fan on the roof. The system would then pull air flow from under the slab and out thru pipe. If I wasnt on site to help dig hole he was going to leave after he had already drilled a few holes in the side wall.

By the way I had ground radar down to see where the footers were in the house for 600. Yea that got fucked up since he hit one along with the wiring for the water heater. According to survey that area was clear.

Forgot about that place you had.


Not a buried roof. More traditional open trusses with tongue/groove planking under metal roof.


Did you have a post-mitigation test done? Remember what the levels were before/after?



If it's as easy as putting a couple vent sumps in, I could manage that. It'll just be a matter of placing them in inconspicuous places. I could see it working on the newer house, since it's only 10 years old and probably does have plastic sheathing under it. The walls were also membrane waterproofed so that would help.


But the older one being 200 year-old stacked rock, and then the floor slab poured in '89, I'm not sure if venting the slab will be effective. Also, it's not like the stacked rock/mortar could ever be sealed so I'm wondering if just venting the slab would be enough. It may just need constant air circulation/ventilation to get it out of the house.
 
Yeah....3,600 sf + 1,600 sf worth of slab replacement.

Depending on the gravel/soil you can sometimes do a few wells.

Without the plastic barrier to keep it from permeating the concrete everywhere it's kinda a crap shoot.
 
I'd have a long duration test completed before deciding anything.

That's most likely the plan. The levels aren't crazy high and will probably drop when the place is opened up regularly, (Both have been mostly vacant for at least a month), but they're high enough to warranty further investigation and I wouldn't want to stay there an do nothing if they don't drop. I'll likely buy a couple monitors and keep an eye on things.

Going to reach out to a couple mitigation companies locally and just see what they'd recommend.
 
Depending on the gravel/soil you can sometimes do a few wells.

Without the plastic barrier to keep it from permeating the concrete everywhere it's kinda a crap shoot.

I don't think permeating solid concrete is the concern....it's more the cracks and joints. Not sure when they started putting sheathing under slabs, but I doubt they go in and tear up slabs on older houses when they put in wells.
 
Curious could you seal the top of the concrete and add another layer?
I was in Co when radon a daily TV topicon the late 80s, since it didn't pertain to me I never paid any attention to it
 
Curious could you seal the top of the concrete and add another layer?
I was in Co when radon a daily TV topicon the late 80s, since it didn't pertain to me I never paid any attention to it

We'd be talking a MAJOR expense. This is a what the place looks like. It's.....interesting.

To pour a new slab over the existing, you'd have to basically get the interior and start over. That's just a tad more convenient than tearing out the old slab.

radon.jpg
 
zomg raydun
it gonna nucleoid you to deaths!

just quit eating bananas while living in the house, it'll even out
 
35 gallons of home made hooch. :homer: Neat looking walls. I'd put a Ford sign on that stove before mitigating the radon. That Chrysler stuff is more poisonous than Radon. :flipoff2:
 
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