Should I bother testing for radon in a gutted and uninsulated house?


Should I bother testing for radon in a gutted and uninsulated house?

Luba Sharapan March 27, 2021Last updated: March 29, 2021

Just finished demo on 100 year old house. With the removal of wall panels and the ancient insulation aka 100-years-of-mold, the house is pretty drafty. I want to test for radon to see if I should build in a radon mitigation system before encapsulating the crawlspace- but wondering if I'll get reliable results with so much passive ventilation going on.

Responses (3)

Luba Sharapan
Luba Sharapan March 29, 2021, 12:35 p.m.

Thank you so much for your detailed reply. The house is in Johnson City, TN, (climate zone 4) which has a high occurrence of radon, so I will operate on the assumption that it is present. Thank you for that nudge! The basement has rock faced block on top of roughly poured concrete. It has a dirt floor.  It will not be used as living space.

I will have to check to see if the 20mil radon block membrane you refer to is available in the US. If not, I will look for 20 mil poly.

The floor is covered with 100+ years of tiny and sharp debris (lots of glass, a million half-buried lathe nails etc). I was planning on using recycled roofing EPS to cover the floor and then poly on top.  Could I dig say a 12"x12"x12" pit underneath the EPS, fill it with gravel, put in the intake end of pvc pipe, cover with EPS, poly and seal? Is there a prescribed depth for this?

And a follow up question...  Is one 4" PVC pipe enough for a 1500 sq ft footprint or should multiple pipes be laid out like an octopus ranging out from multiple points in the floor to one larger pipe that leads to the outside?  Overkill?

Thank you again.

Mike Reynolds March 29, 2021, 2:19 p.m.

Your winters aren’t terribly cold, but you’d still benefit from insulation. I think your plan for the floor is perfect, lay down 2 inches of rigid insulation sheets then poly on top and you’re good. Be sure it’s overlapped a few inches and taped, also be sure it is well-sealed against the foundation walls.

If you can find thicker poly that’s great, but that’s not always easy. If you don’t walk on it much and you’re pretty cautious, the 20 mil may not really be necessary, particularly if its Radon Block may well be shipped to you though so I’d try that first for something more robust and durable.

As for rigid foam, I think that’s a great idea using reclaimed EPS foam panels. For the radon tube, a 12 x 12 x 12 opening to draw air from works as an 'active' stack with a fan, or you could do a passive stack and  you can always add a fan in the future if levels are still high, but this is of course your call.

For a passive stack I'd use perforated septic bed pipes under the poly with the holes facing down, and sure, for 1500 square feet it won’t hurt to put a second one, perhaps on either side of the space. You can attach them with T-junctions.

The exhaust vent tubes are most often taken out through the ceiling and roof, but easiest and arguable best, is to go out at ground level though a rim joist if you can. Sometimes condensation will crystalize and block the opening, if it’s a ground level in a laneway for example, you’d be able to see if its blocked and clear it easily.