Sub-membrane radon mitigation system
Hey Folks – hope you get this question of mine regarding my encapsulated crawlspace. Some years ago you gave me guidance before the undertaking.
To Re-Cap –
Crawl cleaned and graded (no bulk water issues)
Two Thirds of the crawl was then lined with 550 felt underlay. My dirt was clean – few river style rocks, but my friend gave me the felt roll because his crawl was sand and he didn’t use it when he did his crawlspace.
Foundation and dirt floor lined with 20 mil. vapor barrier. Seams overlapped and taped, sealed and mechanically fastened to upper ends of the foundation shelf with fir strips.
All knee walls – rim joist bays – and foundation are insulated to 4″ of Polyiso and foam sealed.
All wire -plumbing holes foam sealed in the crawl. (As was my attic)(stack effect)(attic done later).
The de-humidification in the crawl has been great. It’s managed and maintained to 50% RH.
The dehum does a test cycle each hour, and typically shuts down. No service required. If it does run – it is brief. Temps stays around 63*.
I was encouraged at the time to insulate on top of the liner (or even under). It would help the labor of the dehum. I couldn’t afford any additional insulation at the time.
The efforts in the crawlspace at the time were to understand where all my indoor humidity was coming from. Not Radon.
The R/H in the conditioned area of the home improved after crawl encapsulation, yet in turn, I incorporated a separate whole house dehum to satisfy the conditioned area. The conditioned area of the home is now managed at 50% RH.
A few weeks ago, cleaning out my work area in the garage – I came across a sealed Radon Test Kit. It came with all the crawlspace encapsulation materials when I did the crawlspace. I elected to do the short term test for Radon.
The test results after 48 hours was 4.2 picocuries. It was recommended that I seek help for Radon Mitigation.
I would like to express that I am comfortable with incorporating a Radon fan
to mitigate my Radon issue -( SMD – Sub Membrane Depressurization).
But I have a few questions.
1) How much corrugated pipe do in run? Run the perimeter just off the foundation walls?
2) 3″ or 4″ corrugated pipe?
3) Number of suction points
4) Can you recommend a quiet fan?
Attached are a few pics – in the penciled diagram it references the foot print of the crawlspace. I would like to go through the rim joist into the garage (using a fire ring) then into the attic above my garage and through the roof.
Thanks for your time and considerations.
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