Radon Rough-in Solutions for Crawl Spaces with Angled Rock Outcrops

[Mac Moonfire]

In a crawl space, where rock outcrop are observed at an angle, a 4” layer of aggregate material is difficult to achieve at an angle.
What solutions have you seen to obtain a continuous radon rough-in throughout the crawl space area?

What I have seen thus far is to have sprayfoam the rock outcrop to encapsulate it. This does not however allow gas to flow under the air barrier.

 

[tmurray]

The easiest way may be to run the poly over the rock as part of the air barrier. If any soil gases pass through cracks in the rock, they can be exhausted from under the poly through the extraction pipe.

 

[Wstubbs]

You could sprayfoam and poly over it too.
I think you may need to run a T off your main suction line; run a 2" line from the T to your separate sub-membrane depressurization system (the rock outcrop).
I say that bc using the same vapor barrier from beneath the slab over the rock outcrop might give you some leaks, and may not communicate to the rock area.. I suppose you could use one vapor barrier and add a secondary line.

I used to test and mitigate and estimate systems.
what are the current levels? was the test done in the occupiable space above the crawl?

putting that poly on rock is gonna suck.. you'll need the best adhesive you can find.. unless you can tape the poly to the foundation above the rock.

I'd love to help with anything radon. i did 6 years of it. got loads of info in ma noggin.

 

[Wstubbs]

might just be cheaper option to just mitigate the slab.. retest and go from there to see if you actually need to seal and depressurize the rock area.

 

[tmurray]

You could sprayfoam and poly over it too.
I think you may need to run a T off your main suction line; run a 2" line from the T to your separate sub-membrane depressurization system (the rock outcrop).
I say that bc using the same vapor barrier from beneath the slab over the rock outcrop might give you some leaks, and may not communicate to the rock area.. I suppose you could use one vapor barrier and add a secondary line.

I used to test and mitigate and estimate systems.
what are the current levels? was the test done in the occupiable space above the crawl?

putting that poly on rock is gonna suck.. you'll need the best adhesive you can find.. unless you can tape the poly to the foundation above the rock.

I'd love to help with anything radon. i did 6 years of it. got loads of info in ma noggin.

Normal practice in this area is to seal the poly to the foundation wall.

Not sure if it is required in the US, but in Canada a sub-slab depressurization system rough-in is required by the national code. This includes 4" of crushed rock under the slab and 4" pipe stubbed off and capped. Next edition (2025) is proposing to do a full passive vent system run up through the roof.

 

[Inspector Gadget]

putting that poly on rock is gonna suck.. you'll need the best adhesive you can find.. unless you can tape the poly to the foundation above the rock.

I'd love to help with anything radon. i did 6 years of it. got loads of info in ma noggin.

Right there is the solution: bond the poly to the rock at the foundation above it. Many products would suffice. The simplest approach might be to grab some XPS and a can of spray foam.. and use the foam to bond the poly to the foundation and the XPS to cover it. Won't look purty, but would do the job. An adhesive combined with a suitable tape (I'm thinking flashing tape) would also work.

 

[Plumb-bob]

You could use a thicker poly, such as 10mm, and use strips of plywood or such to mechanically fasten it to the foundation wall. My concern would be any joints in the poly over the rock, difficult to get a good seal on the joints in the field without solid backing.

BC code now requires a full passive system up through the roof, with the pipe accessible for future fan installation if required.

The data shows that +/- 300 people die each year from fires in Canada, and +/- 3000 people die each year from radon.

 

[Wstubbs]

Industrial grade double sided tape

 

[Mac Moonfire]

You could sprayfoam and poly over it too.
I think you may need to run a T off your main suction line; run a 2" line from the T to your separate sub-membrane depressurization system (the rock outcrop).
I say that bc using the same vapor barrier from beneath the slab over the rock outcrop might give you some leaks, and may not communicate to the rock area.. I suppose you could use one vapor barrier and add a secondary line.

I used to test and mitigate and estimate systems.
what are the current levels? was the test done in the occupiable space above the crawl?

putting that poly on rock is gonna suck.. you'll need the best adhesive you can find.. unless you can tape the poly to the foundation above the rock.

I'd love to help with anything radon. i did 6 years of it. got loads of info in ma noggin.

this is for a new build. Radon testing has not been conducted. In my area, we’ve typically used either poly or 2 lbs spray foam (air-permeable) with a skim coat on top. The poly is sealed to the foundation walls with a thick, continuous bead of acoustic sealant at the same level as the skim coat. We'll continue with this approach but I am open to hearing better options.
Thank you for your input, everyone!