A new-construction radon system is a passive rough-in installed during the build: gravel gas-permeable layer, sealed vapor barrier, and a vent pipe running from beneath the slab through the roof, with an attic junction ready for a fan if tests later demand one. Roughed in before the slab pours, it costs $400 to $900. Retrofitting the same protection later costs three to five times that.
Once the slab is down and the walls are up, adding radon protection means coring concrete, snaking pipe through finished space, and putting a fan on the outside of a house someone just paid to make beautiful. Before the pour, it's a length of pipe and an afternoon.
If you're building in The Pinehills, on a Carver lot, or adding a wing to a Duxbury colonial, this page is the one to read before your foundation contractor shows up.
Four inches of clean gravel under the slab, letting soil gas move to the collection point instead of hunting for cracks.
A tee or perforated loop set in the gravel: the future system's lungs.
Poly sheeting over the gravel, seams lapped and sealed, penetrations caulked. This alone cuts entry substantially.
Schedule 40 PVC from the collection point, up through interior framing, out the roof like a plumbing vent. Labeled at every floor so no future tradesperson mistakes it.
An electrical rough-in and a straight pipe section sized for a fan, so activation later is a two-hour job, not a renovation.
A passive stack works on thermal draft alone and often keeps a tight new build under 4.0 by itself. Often is not always: this geology can overwhelm passive draft. The protocol is simple. Build with the rough-in, test after occupancy under closed-house conditions, and if the number wants more, drop the fan into the junction that's been waiting for it. Total worst case: you spent $400 to $900 to make a $1,500 problem into a $400 one.
Numbers make this decision by themselves:
During construction: gravel you were probably spec'ing anyway, a membrane upgrade measured in hundreds, a pipe run installed while walls are open, an electrical rough-in while the electrician is already on site. Total: $400 to $900.
The same protection, retrofit two years later: coring a finished slab, routing pipe through finished living space or up an exterior wall, a dedicated electrical run, patching and paint. Total: $1,500 to $2,500+, plus the aesthetic compromises a retrofit forces.
The failure case: skip it entirely, test high after occupancy with a toddler's playroom on the slab, and pay retrofit price under time pressure. This is the most common radon story in new construction, and the entire reason rough-ins exist.
The rough-in is insurance where the premium is a rounding error on the build and the payout is avoiding the worst version of the problem.
There's a persistent assumption that new construction means low radon: tight envelope, modern slab, vapor barrier, surely fine. The physics runs the other way. A tight house holds whatever enters, and a brand-new slab sits on freshly disturbed soil with its gas pathways rearranged by excavation. New builds in this county test high regularly, including slab-on-grade homes with no basement at all. The Pinehills-style slab construction puts the living space directly on the soil interface, which is exactly why the sub-slab layout deserves attention before the pour, not after the certificate of occupancy.
We coordinate with your foundation and framing schedule, not against it: gravel and collection before the pour, stack during rough plumbing, done. Spec-home buyers in this county increasingly ask about radon readiness at showings, and "passive system installed, fan-ready" is a line that costs you almost nothing and reads like quality.
When we rough in a system, the documentation travels with the house: what's under the slab, where the stack runs, what the attic junction is sized for, and a label at every floor penetration so no future electrician or plumber mistakes the radon stack for a vent line and tees into it (it happens, and it ruins the system silently). For builders, that documentation packet is also your answer when a buyer's inspector asks about radon readiness: you hand over a diagram instead of a shrug. Small thing, reads like professionalism, costs nothing.
Two touchpoints, both short: the gravel-and-collection work happens after footings and before the slab pour (half a day, coordinated with your foundation contractor), and the stack goes up during rough plumbing when the walls are open anyway. We work around your schedule, not the reverse, because a radon crew that delays a pour doesn't get called back.
$400 – $900
passive rough-in; active conversion priced separately
Depends on the county. The Massachusetts building code adopts the radon control appendix as mandatory for new construction in the state's highest-potential counties: Worcester, Middlesex, and Essex. Plymouth County sits in Zone 2, so the rough-in is optional here, which is exactly why so many new South Shore builds skip it and test high after occupancy. One more detail worth knowing: Massachusetts specifically does not require a radon test as a condition of your certificate of occupancy. Nobody checks the number unless you do.
Yes, and slab homes need it just as much. No basement means the lowest lived-in level sits directly on the soil.
Any new slab connected to living space is worth protecting while the ground is open.
After occupancy, first heating season if possible, closed-house protocol. That number decides whether the passive stack stays passive.
Radon Mitigation for Plymouth and Plymouth County. Test it. Fix it. Prove it's fixed.
(508) 503-6186