Determining the number of access points


Since our pricing structure depends on the number of access points (suction points) we must install, you probably want to know how we determine the appropriate number of access points!  Like everything else in radon mitigation, there’s no simple answer. We can, however, explain how to get a good idea ahead of time.

As a quick review, suction points (same as an “access point”) are where we connect the PVC pipe to the area below your slab.  We will drill a 5″ circle in your concrete & excavate 5-10 gallons of dirt/fill/gravel to create a “suction pit”.  Once we insert the 4″ PVC pipe into the suction pit and connect the fan, your mitigation system will actively pull air from beneath your slab.

radon suction pit hole

So, how many do we need for your home?  We always try to install a single access point when possible…but sometimes it just doesn’t work.  Some reasons that we may not get good “sub-slab communication” (the ability to remove air from beneath your entire slab) are:

  • Tight/compact sub-slab aggregate.  This could be tightly packed clay or dirt.
  • Saturated soils beneath the slab. Naturally, wet dirt doesn’t provide good airflow.
  • Foundation walls.  In newer construction, it is common for a home’s center beam to rest on a series of posts. These posts in turn rest on either concrete pads, or a full footer.  If there’s a footer beneath your slab in the center of your home, we cannot suck air through it!  We’ll need to install another suction point on the other side of the slab, so we’re drawing air from both sides of the hidden foundation.
  • Very large homes.  Usually, a single suction point will only work effectively on a slab that is under 2000sf

Contrarily, there are some conditions that allow us to pull air very efficiently across the entire pressure field (aka your whole sub-slab area), and only require a single access point:

  • Very small slab footprint
  • Coarse aggregate beneath your slab (large stones, disturbed soils, etc)
  • Interior drain tile (buried perforated pipe below the slab that runs around the perimeter of the basement)

Aside from the size of the basement, there is no way to know about these other conditions until we begin. As such, you might see some notes about a “phased” approach to your mitigation system installation.  To keep costs low, we will generally try to succeed by using only one access point. If we determine through PFE testing (pressure field extension testing) that we’re not getting good sub-slab communication, we may stop the installation and request approval to install an additional access point.  Sometimes, we will simply install the system with one access point and perform our post-mitigation testing. If the tests don’t come back at a satisfactory level, we’d continue the next “phase” of the installation by returning to the home and installing another access point. There is an additional cost involved with an extra access point, which is why we will always try to succeed with a single suction point.

To learn more, call our office at 330-267-9550.

 

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