Passive radon systems in new builds: what to verify before closing
A passive radon system in a new house is buried infrastructure: a permeable layer, a membrane, sealed penetrations, and a vent pipe, almost all of which disappears the moment the slab is poured and the drywall goes up. You are buying it on trust.
That is not an argument against new construction. It is an argument for asking a short list of questions while you still have leverage — during the walkthrough, inside the warranty period, and before the builder relationship becomes a memory.
What a complete rough-in includes
Four elements, all installed before the slab: a gas-permeable layer of clean aggregate beneath the slab, a sheet membrane over it, sealing at joints and around penetrations, and a vent pipe running from the sub-slab layer up through the house and out above the roofline.
A fifth element is optional but valuable: an electrical junction near the pipe in the attic or garage, so that a fan can be fitted later without new wiring. Builders who include it are anticipating activation, which is a good sign.
The pipe should be labelled. Where it is, the label is normally the fastest way for a future owner, inspector, or contractor to identify what they are looking at.
What to ask the builder, in writing
Ask whether a passive system was installed, and to what standard or code provision. Ask where the vent pipe runs and where it terminates. Ask whether an electrical junction was provided for future fan installation. Ask whether the house has been tested, and if so, for the report.
Get the answers in writing rather than at a walkthrough. Not because anyone is expected to be evasive, but because the person answering on site is often not the person who poured the slab, and a written answer is what you can act on later.
- Was a passive radon system installed, and under which code provision?
- Where does the vent pipe run, and where does it terminate?
- Is there an electrical junction provided for a future fan?
- Has the completed house been tested? If so, when, where, and under what conditions?
- What does the warranty cover if a post-occupancy test comes back elevated?
What you can verify yourself
Look in the attic for a PVC riser, commonly three or four inches, heading out through the roof — capped or open, often labelled, and traceable downward toward the slab. That is the passive system.
Check that the roof termination is above the roofline and away from openable windows. Check whether the pipe passes through a garage or attic where a fan could legally be mounted; a pipe running entirely through conditioned interior space is a genuine constraint on future activation, because fans must sit outside occupied space.
And check the basement or slab for a capped stub, which sometimes indicates a rough-in that was never carried upward.
Test early, for a reason that is not about radon
Test the completed house under closed-building conditions as soon as you are living in it normally, and certainly inside the builder warranty period. The radon reason is obvious. The other reason is contractual: an elevated result discovered while a warranty is live is a different conversation from the same result discovered three years later.
If the result is elevated and a passive rough-in exists, activation is usually the answer and is usually far cheaper than a retrofit. That conversation goes better when the builder is still on the hook for whether the buried half was installed correctly.
What would change this page
This is a standing reference rather than a report of a single event. Any of the following would require it to be revised, and the revision would be logged with a date:
- A state we serve changes what new residential construction must include for radon.
- Model code revisions change the specified components of a passive system.
- Common builder practice on electrical provision for future fan installation changes materially.
Passive systems in new builds: common questions
How do we tell whether our house has a passive system?
Look in the attic for a PVC riser of roughly three to four inches exiting the roof, frequently labelled, that traces back down toward the slab. A capped stub through the basement floor is another indicator. If neither is present, the builder or the permit record can confirm.
Is a passive system worth anything if it did not bring the level down?
Yes — it is most of the cost of a mitigation system already installed. Activation adds diagnostics, sealing, a fan sized to measured conditions, and a verification test, using pipe that already exists. That is normally substantially cheaper than a full retrofit.
Should the builder pay for activation?
That depends entirely on your warranty and purchase documents, which is why reading them before the period lapses matters. Some builder warranties address radon explicitly and others do not. It is a contract question, not a radon question.
Is testing possible before closing?
Often yes, and it is worth asking. The complication is that a short-term test needs closed-building conditions and normal HVAC operation, which an empty, newly finished house may not have. A test run in an unconditioned house describes an unusual state rather than how you will live in it.
Where to go next
- Activating a passive system — Activation is an engineering evaluation of a rough-in you did not watch being built — not simply a fan purchase.
- When to retest — Every two years, plus after anything that changes how the house meets the soil or how it moves air.
- Finished basements — A finished basement raises both the exposure and the cost of fixing it — which is why the timing question matters more than the technique.
- Average cost explained — What the published ranges mean and where your house falls in them.
States this bears on
- Nebraska radon resources — State credentialing, radon-resistant new construction requirements, and negotiated remedies.
- Colorado radon resources — No state licence, but a required warning statement before a sale — and a testing quirk worth knowing.
- Ohio radon resources — A genuine state licence covering testers, contractors, and labs — and a disclosure form that asks directly.
Related from the newsroom
- How RRNC reaches a house — Four steps between a provision existing and your house having one — and why none of them replaces a test.
- Fan technology — Real improvements in selection, monitoring, and efficiency — against a design principle that has not moved.
The questions above cost nothing to ask and are far easier to raise before closing than after. A passive system is worth having; knowing what was actually installed is worth more.
Confidence and limits of this page
Every decision resource on this platform states its own boundaries. This is not a disclaimer — it is the part of this dispatch you should read before relying on it.
- What we knowClaims on this page we stand behind, each traceable to an approved source or to observable structure.
- Radon-resistant construction provisions exist in model code and reach states and local jurisdictions unevenly rather than following one national rule.
- A passive system installed under those provisions reduces risk without establishing a result; only a measurement does that.
- What we do not knowQuestions you may reasonably have that this page does not answer.
- Which local jurisdictions have adopted which provisions today, since adoption happens at a level below the state and is not collected in one place.
- How consistently adopted provisions are enforced in practice, which would require inspection records we do not hold.
- What research would settle itWhat it would actually take to answer the above — naming it is the difference between honesty and hedging.
- A survey of local adoption and amendment, which would need primary collection from municipalities rather than from model code text.
- Measurements in new houses built under passive provisions, which would show how much the provisions actually accomplish before activation.
- What we do not claimClaims you might expect to find here and will not, with the reason.
- We do not claim any jurisdiction has adopted a provision unless we cite the adopting authority.
- We do not claim a new house is exempt from testing, because passive provisions reduce risk rather than remove it.
- What we cannot independently verifyFacts this page relies on that we could not confirm ourselves.
- The current adoption status in any specific municipality, which changes on local schedules we cannot monitor from here.
- The present content of the cited code and guidance documents, for the network reason stated in our methodology.
Sources
- U.S. EPA — Radon
- U.S. EPA — Consumer’s Guide to Radon Reduction
- U.S. EPA — A Citizen’s Guide to Radon
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