Radon-Resistant New Construction: Estimator Bidding Checklist
Radon-resistant new construction (RRNC) provides a critical public health benefit by helping lower the risk of lung cancer caused by indoor radon exposure. More than 1.5 million new homes have been constructed with radon-resistant features since 1990, based on annual builder surveys conducted by the National Association of Home Builders (NAHB) Research Center. For general contractors and trade estimators, incorporating these passive features during the initial build is typically far less expensive than mitigating a structure after completion. Using common materials and standard installation techniques, builders can incorporate radon resistance into their bids without requiring specialized site skills.
Checklist Item 1: Gas-Permeable Sub-Slab Layer
The foundation base serves as the initial collection zone for soil gases, allowing them to move freely beneath the slab rather than forcing their way into living spaces. Estimators should price a 4-inch layer of clean, coarse gravel directly beneath the concrete slab foundation. In construction plans, this bed is often designated as the gas-permeable layer or air flow layer.
Jobsite conditions and material availability can influence this takeoff item. In regions where gravel is cost-prohibitive or unnecessary, project specifications may permit alternatives such as perforated collection pipe or specialized collection mats. Estimators coordinating site prep and sub-slab fills should confirm whether standard gravel or an alternative pipe system is detailed on the structural drawings before finalizing earthwork bids.
Checklist Item 2: Polyethylene Soil-Gas Retarder
Directly above the permeable stone, the building envelope requires a continuous barrier to block gas migration. The estimate must carry heavy duty plastic sheeting, specifically 6 mil. polyethylene, or an approved vapor retarder placed on top of the gravel bed prior to pouring the slab. This layer serves two distinct functions that estimators must account for:
- It stops naturally occurring soil gases from pushing into the interior living spaces.
- It prevents wet concrete from seeping downward and clogging the voids in the 4-inch gravel bed during the foundation pour.
Estimators should review lap allowances and edge detailing when taking off membrane quantities to ensure continuous coverage across the entire foundation footprint.
Checklist Item 3: Vertical PVC Vent Pipe Routing
Passive systems rely on natural drafting to route soil gases safely beyond the roofline. Estimators should budget for a 3-inch or 4-inch solid PVC Schedule 40 pipe, identical to common plumbing pipe. The installation sequence must be divided accurately across bid packages:
- Rough-in: The pipe is embedded into the sub-slab gravel layer and stubbed up before the concrete slab is placed.
- Vertical run: The pipe extends vertically through the conditioned envelope of the building and penetrates the roof.
- Termination: The pipe discharges gas safely outside above the home.
- Identification: The pipe run must be visibly labeled as a "Radon System."
Plumbing subcontractors or certified radon professionals listed through the National Radon Proficiency Program (NRPP), the National Radon Safety Board (NRSB), or state radon coordinators can carry this scope.
Checklist Item 4: Caulking and Foundation Penetration Sealing
Preventing soil gas entry requires meticulous sealing of all foundation boundaries. Bids should include material and labor for polyurethane caulk applied across every joint, crack, and opening in the concrete foundation floor and walls. This scope includes sealing the entire slab perimeter crack where the floor meets the foundation walls, as well as sealing around plumbing stubs, structural columns, and utility penetrations. Coordinating this work ensures that no unsealed gaps bypass the membrane beneath the slab.
Checklist Item 5: Attic Junction Box for System Activation
Even though RRNC uses passive airflow techniques, specifications often prepare the building for active mechanical depressurization if post-occupancy testing reveals elevated radon concentrations. Estimators must include an electrical junction box (outlet) installed in the attic near the vent pipe. This rough-in provides dedicated power for an in-line exhaust fan if a more robust system is required later, sparing the homeowner significant retrofit wiring expenses.
Scoping Trade Packages and Green Building Programs
Because RRNC features span earthwork, concrete, plumbing, sealing, and electrical rough-ins, clearly defining trade boundaries prevents costly bid gaps. Detailed scopes should align with technical guidelines from the US EPA Radon-Resistant Construction Basics and Techniques page. Establishing clear assignments in your bid exclusions and clarifications ensures the plumber knows they own the vent stack, the concrete sub accounts for the 6 mil. sheeting and 4-inch gravel, and the electrical contractor includes the attic outlet.
Radon-resistant features also support verification requirements across three major voluntary labeling standards: the EPA Indoor AirPlus program, the U.S. Green Building Council LEED for Homes Rating System, and the National Association of Home Builders (NAHB) standards. Reviewing the EPA's radon-resistant construction guidelines alongside project specifications ensures that all five core RRNC components are accurately captured on bid day.
Sources
Published October 29, 2026. No affiliate links on this page. Facts come from the sources linked above; check them for updates.