How do I inspect a passive radon system?

Passive radon systems, preferably called Radon-Ready New Construction (RRNC) or “pre-plumbed” radon systems require inspection before concrete is poured.  In this guide we’ll go over how to inspect an SGC radon mat system before a concrete slab is poured.  Many of the same steps are used for crawlspaces.  There are very few differences between single family and multifamily.

Let’s get started.

Radon Standards

It is important to note that there are many different radon standards adopted across the US.  In this article we use the words “code” and “standard” interchangeably.  At PDS, we recommend using ANSI AARST standards as they are the consensus standards by modern radon professionals and the most up-to-date peer reviewed standards available.  They are also the standards adopted by many US states.  Lastly, the US EPA often points to these standards specifically.  You may view these radon standards for free at standards.aarst.org.  The most commonly adopted are RRNC 2.0 (RRNC-2020-1022) and CC-1000-2018-0523.  IRC appendix F or AF is sometimes adopted as well.

The National Radon Proficiency program certifies SGC compliance inspectors.  This is typically a one day course for radon professionals and covers many types of radon systems.  At PDS, we highly recommend using an SGC compliance credentialed inspector.  Learn more about trade school courses here.  This guide is not a replacement for a qualified SGC inspector.

Soil Prep

PDS Radon Supply’s Geotextile Soil Gas Collector does not require any special soil preparations in order to be effective.  However, many codes require a sand or gravel layer.  See the code links above.

What is important to note is: where the radon mat is placed.  The radon mat is most commonly placed on top of the sand/soil/gravel layer just underneath the barrier.  PDS’ mat does not require trenching.

It is acceptable and not uncommon to place the mat below a gravel or sand layer.  The most important consideration is: is the SGC radon mat installed below the vapor barrier?  If so, then it should be effective and should pass inspection.  If the SGC mat is above the vapor barrier it will not be effective and should be flagged as an immediate fail.

Be sure that the EZ riser plenum is “stubbed up” at least 6″ but preferably 1-2′ higher than the gravel layer and vapor barrier layer (see photo above).  One of the biggest mistakes we see is sub-slab prep teams burying the risers.  This is a huge mistake and will require you to destroy fresh slab with a jackhammer to find your air collection system.  Secure the riser plumb using a PDS Stub Stabilizer, zip tie, and rebar

Joints, Junctions, and Seams

Is the radon mat fully taped at each seam like in this video?  PDS’ radon mat is “make your own puzzle pieces”, which means radon mat junctions are cut with a box cutter and fit together on-site with seam tape and then secured with staples.  No costly or specialty fittings required!  Does the tape stick firmly to the geotextile fabric?  Is the black inner layer fully covered up?  If so, the system should function.  If the tape bubbles or peels off, retape and ask your sales consultant for a higher quality tape for the next job.

Vapor Barrier

PDS Radon mat is special because it’s geotextile fabric surrounds the mat fully.  This allows for effective installation without a vapor barrier.  Many codes still require a vapor barrier, but it is not required to function as long as the taped seams are strong.  It is not uncommon to see single family homes or other projects in arid states have no vapor barrier whatsoever.  Check the code requirements, but trust that the SGC geotextile fabric can keep concrete out and the airflow high.  Again, is the mat below the vapor barrier?  Are the seams securely taped?  If so, then you’re in good shape.

If there is no vapor barrier or the vapor barrier has not been installed yet, then it is very important to secure the mat to the substrate using common construction methods.  Most commonly SGC staples or steel nails.  Securing the mat to the ground ensures that the wind will not blow it away.  It also ensures that it will not float up.  You do not want the mat to be inside the slab, but below it.  With a sub slab vapor barrier, the stapling considerations are less important, since the mat cannot float into the concrete layer.

EZ Riser and Vertical Pipe Runs

As notated above, the radon mat must be run vertically through the slab.  The radon mat acts as a soil gas collector, the vertical pipe runs act as the exhaust system; both are key components.  The RRNC pre-plumb system needs to run through the entire building up through the roof to be effective.  Before concrete pour, it is most important that the EZ risers are secured, stable, and stubbed up high enough so as not to get buried inside the slab itself.  Clearly mark them with CAUTION labels designating this as radon piping.

Post Pour and Pre-drywall

While the sub-slab system is very important, we find many GCs forget to finish their radon system!  The sub-slab is only half of the system.  See this video series for more visually important information.

The EZ risers vertical stacks must now be joined with common PVC joints to continue the pipe run as straight as possible up through the roof of the building.  This allows the radon gas to escape.  Radon gas will not escape passively all seasons of the year so be sure to test and activate (more below).

Radon Fan Pre-wire and Spacing

Pre-wire 120V access within 6′ of the radon PVC stack outside the thermal envelope of the building.  Commonly, in an attic space or roof area.  Radon fans are not allowed indoors in the USA.  Read why here.  Radon fans are about the size of a basketball.  Don’t hide the stack too close to the soffit or in an area that you would be unable to cut the PVC and install it comfortably should activation be necessary.  If you forget to leave space or leave power, you’re costing yourself a lot of money when activation time comes.

Testing and Activation

By now you’ve had two inspections: one pre-concrete pour; and one pre-drywall/sheetrock.  Once the building envelope is completed and the HVAC is running, you may test the building for radon.  You may be thinking: “pfft, there won’t be radon, we just ran a system”  Wrong.  Read more on why passive systems are leaving modern radon nomenclature here.

Since radon levels vary so dramatically seasonally as well as with different HVAC systems, it’s extremely important to use a certified radon professional.  Their standards are many dozens of pages long and their training takes many weeks.  It’s not as simple as tossing a passive or amazon device in one small section of the building and calling it a day.

On large multifamily footprints, in North America, it is almost a guarantee that a non-zero number of stacks will need to be activated with a radon fan to protect occupants.  Colorado for example you can expect to activate 52% of single family homes or over half the stacks in a multifamily complex.  By building radon ready and following these protocols you’re saving the owners considerable time and money.  You’re also protecting their air quality and health.  Kudos!

Give us a call with any additional questions.

Thanks for choosing USA-made soil radon gas collection mat!