Radon-resistant new construction

Why new homes in Zone 1 still test high

A common assumption in new developments — Dakota Dunes, Sergeant Bluff, the newer plats on Sioux City's north and west sides — is that a new house means a radon-safe house. The soil doesn't care about the build date. New homes sit on the same uranium-bearing glacial soils as century-old ones, and modern construction can actually concentrate radon: tighter envelopes hold soil gas in, and high-efficiency HVAC can increase the stack effect that draws it up. In Zone 1 counties, new builds routinely test above 4.0 pCi/L. Every new home should be tested after occupancy — no exceptions for age.

What radon-resistant new construction (RRNC) includes

RRNC — sometimes called a "passive system" or "radon rough-in" — is a set of inexpensive steps taken during construction that make radon control nearly free later:

• Gas-permeable layer: 4 inches of clean aggregate under the slab, so soil gas can move freely toward a collection point instead of pooling under random sections of floor.
• Soil-gas collection point: a tee fitting or short length of perforated pipe set in the aggregate, stubbed up through the slab.
• Vapor barrier: heavy polyethylene sheeting over the aggregate before the pour, seams overlapped, penetrations sealed.
• Vertical vent stack: 3–4" PVC running from the collection point up through the house's interior, through conditioned space, and out the roof — exactly like a plumbing vent. Run passively, warm-house stack effect alone pulls some soil gas up and out.
• Fan-ready wiring: an electrical junction box in the attic beside the stack, so a fan can be added in under an hour if it's ever needed.
• Sealing details: caulked slab joints, sealed sump lid, gasketed penetrations — cheap at construction time, fiddly to retrofit.

Done during the build, all of this typically adds a few hundred dollars in materials and labor — a fraction of a retrofit — and the vent stack hides inside walls instead of running up your siding.

Passive isn't a guarantee: test, then activate if needed

A passive stack reduces radon, but in the soils around here it often isn't enough by itself. The fix is the whole point of the rough-in: activation. An inline radon fan is mounted on the existing stack in the attic, wired to the waiting junction box, and the passive system becomes a full active sub-slab depressurization system — usually in a single short visit, with no coring, no new pipe runs, and no visible change to the house.

For builders and contractors

If you're building in Woodbury, Plymouth, or Union County, offering RRNC as standard is an easy differentiator in a market where buyers increasingly ask about radon at showing time — and where the inspection-period radon test has become routine. We work with builders on:

• Rough-in design and specs per EPA/ANSI-AARST new-construction standards — collection layout, stack routing that stays in conditioned space, labeling, and fan-ready electrical.
• Slab-stage installs timed to your pour schedule — the collection point and barrier go in between plumbing rough-in and pour with no impact on your critical path.
• Post-occupancy testing for your buyers, and activation on any home that needs it — so a radon question never comes back to your warranty desk.

Additions, remodels, and finished basements

The same thinking applies when you change an existing house. Pouring a slab for an addition? A collection point and stub under the new concrete costs almost nothing while the ground is open. Finishing your basement into living space? Test first — mitigation is cleaner and cheaper before drywall and flooring go in, and a bedroom or family room at the lowest level raises the stakes on whatever number the house runs at. We regularly coordinate directly with remodel contractors so the radon work slots into their schedule instead of disrupting it.

The bottom line for Siouxland builds

New construction is the one moment radon control is nearly free. If you're building: rough it in. If you've bought new: test it, and activate the stack if the number's high. If you're adding on or finishing a basement: deal with it while the ground is open. Every one of those conversations starts the same way — send us the details or call (712) 526-4497 and we'll tell you what the house actually needs, and what it doesn't.