Is Your Brand-New Home Already Letting Radon In? 3 New Construction Mistakes You Can't Afford to Ignore

April 15th, 2025 by Melanie Miranda

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When it comes to building a new home, there’s a growing awareness around energy efficiency, layout, and even resale value—but one invisible threat often slips through the cracks: radon mitigation passive systems.

At Apex Radon Solutions, we’ve inspected countless new construction homes across Connecticut, and the number of improperly installed passive systems is alarming. Builders are trying to do the right thing—but without the guidance of a radon professional, systems are often installed incorrectly, making them ineffective when you need them most.

Here are three recent examples from homes in Greenwich, CT, Cos Cob, CT, and Danbury, CT where new builds fell short of proper radon mitigation standards—and what you can learn before you seal the walls and sign the paperwork.

Greenwich, CT – A Passive Pipe to Nowhere

In an elegant new colonial home in Greenwich, the builder proudly pointed to the passive radon system installed “just in case.” But when we inspected the home after the drywall went up, the pipe ended in the basement slab—capped and sealed. There was no extension through the home, no attic access, and no electrical hookup for a fan.

Lesson: A passive radon system isn’t just a pipe in the slab. It must vent through the roof and include an electrical source in the attic to easily convert the system to active if testing shows levels above 2.7 pCi/L.

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Cos Cob, CT – No Crawl Space, No Coverage

In a high-end townhome development in Cos Cob, a homeowner requested radon testing after moving in. The reading came back at 6.1 pCi/L. Their builder had skipped the radon mitigation system altogether because the home had a sealed crawl space—but they didn’t consider that radon can still enter through foundation cracks and utility penetrations.

Lesson: Crawl spaces need radon protection too. RRNC standards include sealed liners, ventilation piping, and sub-membrane depressurization. Every foundation type—slab, crawl, or basement—requires a plan. $Is Your Brand-New Home Already Letting Radon In? 3 New Construction Mistakes You Can\'t Afford to Ignore - Image 2$

Danbury, CT – Passive System Activated... Without Testing

In a newer ranch home in Danbury, the builder had already installed a radon fan and plugged it in—before any radon testing was done. The fan is only installed and activated with a higher-than-desired radon level. The homeowner was unsure if the fan was necessary or even functioning. When we inspected, the fan was operating, but it was connected to a pipe system installed within inches of the roofline, making future maintenance nearly impossible.

Lesson: RRNC guidelines recommend testing after the certificate of occupancy is obtained, or the CO; and fan installation must cover accessibility and long-term serviceability.

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What Is RRNC (Radon-Resistant New Construction)?

RRNC is a building standard designed to minimize radon exposure in new homes. A properly installed system includes:

A gas-permeable layer beneath the slab (e.g., gravel)
A polyethylene vapor barrier
A 3" or 4" PVC vent pipe running vertically through the home and out the roof
An attic electrical outlet within 6 feet for future fan installation
Airtight sealing of openings, sump pumps, and utility penetrations (recommended)

Before You Close the Walls: Have You Covered Radon?

If you're in the design, construction, or final walk-through phase of building your new home, ask your contractor:

Does the passive system vent through the roof?
Is there an electrical outlet in the attic?
Has a radon test been conducted post-CO?
If the builder puts the fan, which is not part of the code or recommended, make sure the fan is not installed in a liveable area, such as the basement.

Protect Your Investment—and Your Health

Apex Radon Solutions specializes in radon mitigation for new construction homes, working alongside builders, developers, and homeowners to ensure systems meet both local code and RRNC standards. If you're building in Connecticut, we’re ready to help ensure your home is radon-resistant from the ground up.