A multi-zone Indian Hill custom build: when one suction pit is not enough

The starting point

A 2003 custom home in Indian Hill, 5,200 square feet finished, on a 2.8-acre lot. Two distinct foundation footprints joined at a transition wall: 3,800 sqft full poured-concrete basement under the main wing (kitchen, family room, dining, study, three bedrooms upstairs), and 1,400 sqft crawl space under the detached-style master suite that sits at a slightly lower grade with its own roofline.

The owner had been in the house since 2009 and never tested. Their daughter, recently qualified in oncology nursing, ran a long-term alpha-track test as a winter project and got back a year-averaged reading of 9.1 pCi/L. EPA recommends mitigation above 4.0 pCi/L. The owner called the our dispatch line with the result.

Why one suction pit was not the right answer

Indian Hill custom homes built in the 1995-2010 window often have multi-zone foundations because the lots are large enough for sprawling layouts and the architects designed wings rather than rectangles. The radon-mitigation challenge: a single suction pit pulled at one point produces negative pressure that drops off with distance through the sub-grade soil. At 30+ feet from the suction pit, the pressure differential becomes too small to overcome competing soil-gas paths. Multi-zone homes need multi-zone mitigation.

In this house specifically:

• Main basement zone: roughly 50 feet long by 70 feet wide. A single suction pit at the center could pull the perimeter, but barely.
• Master suite crawl space: 28 feet long by 50 feet wide, separated from the main basement by a foundation transition wall with no through-grade airflow. A suction pit in the main basement would not reach this zone at all.

The mitigator's diagnosis: two completely independent suction zones, two stacks, two fans, two manometers.

The design

Quote: $4,250 fixed, broken out:

Zone 1: Main basement (active sub-slab depressurization) - One suction pit core-drilled near the geometric center of the basement - Sealed sump-pit lid (existing sump on the south wall) - Polyurethane sealing of three visible slab cracks (typical settling cracks, 8-12 feet long each) - Stack routed through interior closet chase to attic, exterior to roofline - Radonaway RP145 fan in attic-mounted enclosure - Manometer at the basement ceiling near the sump

Zone 2: Master suite crawl space (sub-membrane depressurization) - Reinforced 12-mil polyethylene barrier across crawl-space dirt floor and 8 inches up perimeter foundation walls - Butyl-tape and polyurethane caulk perimeter sealing - Sub-membrane suction pipe through the barrier near the geometric center of the crawl space - Stack routed through master-suite mechanical chase to attic, exterior to roofline (separate from Zone 1 stack) - Festa AMG250 fan in attic-mounted enclosure (sized for the larger air-volume crawl space) - Manometer at the master-suite mechanical room ceiling

Both zones: - Dedicated 15A circuits (one per fan) - 48-hour post-install verification monitors (one per zone) - 12-month follow-up retests on both zones

Install day(s)

This was a two-day job. Day 1: full basement work plus the basement-side stack to roofline (Zone 1). Crew of three on site 7:30 AM through 5:00 PM. Day 2: crawl-space barrier installation plus the master-suite-side stack to roofline (Zone 2). Crew of two on site 7:30 AM through 3:00 PM.

The crawl-space work was the slowest part of Day 2. Indian Hill custom-build crawl spaces often have HVAC ductwork, plumbing rough-ins, and lighting wired through the joist bay above the dirt floor, all of which need to be carefully worked around when laying the polyethylene barrier. Plus the master suite's HVAC return air ran through a chase that crossed the planned stack route, requiring a small offset in the stack routing.

End of Day 2 readings: Zone 1 manometer at 0.95 inches water column negative, Zone 2 manometer at 0.7 inches. Both healthy.

The 48-hour retest

Two continuous radon monitors placed simultaneously: one in the main-house family room (Zone 1), one in the master-suite bedroom (Zone 2). 48-hour averages:

• Main house: 0.8 pCi/L
• Master suite: 1.1 pCi/L

Down from a year-averaged 9.1 pCi/L household-wide (the alpha-track test averaged across both zones since the homeowner had placed it in the main hallway near the transition between zones). The post-mitigation reduction is even larger if the alpha-track was somewhat under-reading the master suite.

What the homeowner paid

Total: $4,250 fixed. About 1.7x what a standard single-zone Cincinnati basement install costs, reflecting the doubled scope and longer install time. Annual electricity for both fans combined: about $190. Compared to a single-zone-and-hope-for-the-best approach (roughly $2,400), this case spent an extra $1,850 to address a real geometry constraint, and got a real result.

Why this case is unusually instructive

Most Cincinnati radon mitigations are single-zone work. Multi-zone homes are 5-8% of the market, concentrated in Indian Hill, Mariemont, parts of Hyde Park (older subdivided estate lots), and a handful of newer Mason and Madeira custom builds. If your home has multiple foundation types under one roofline, expect a multi-zone quote. If a contractor quotes a single-zone install on an obviously multi-zone home, get a second opinion.

Things to ask during the on-site assessment: - "Are you treating both zones independently, or one zone with a hope of carryover?" - "What suction-pressure measurements did you take at each zone?" - "Where will each manometer be located, and can I see them both from a single spot during routine checks?" - "Are both zones included in the post-install verification, or only one?"

A credentialed NRPP mitigator who has done 50+ Indian Hill or Mariemont multi-zone installs will answer all four cleanly. A contractor who hesitates or argues that "one zone covers both" probably has not done many.