Radon is a naturally occurring radioactive gas that commonly migrates from soil into homes through foundation joints, pipe chases and sump pits — and Colorado, including the Denver area, has many high-risk zones. Building a custom home on your lot gives a major advantage: mitigation can be installed as part of the structure rather than retrofitted. That means you can choose either a passive radon-resistant new construction (RRNC) system — a buried suction pipe and continuous vapor barrier designed to be activated later — or an active system with a continuously operating fan installed during construction for immediate protection.
Typical new-construction installations start before the slab is poured. Contractors place a layer of clean gravel or a perforated collection mat directly over the compacted subgrade, then a continuous vapor/soil-gas barrier (commonly 6-mil or thicker polyethylene) with sealed seams and sealed perimeter connections. A 3–4 inch PVC suction pipe (standard is 4″) is run from that gravel bed up through the slab and wall cavity to attic or roof level; penetrations are carefully sealed at the slab to maintain sub-slab depressurization. For active systems, an in-line radon fan is mounted above the living space (attic, garage, or exterior wall) and wired to a dedicated circuit; a simple pressure gauge (manometer) is left visible to monitor operation. All vents are routed to terminate above the roofline and away from windows and fresh-air intakes, pipe runs are kept upright or sloped to avoid traps, and any sump pits or utility penetrations are sealed to reduce bypass leakage. Insulating or protecting exposed pipe and choosing a frost-resistant fan location are common considerations for Denver’s climate.
At RKM Homes we incorporate radon planning into the design and scheduling from the start so the mitigation contractor can coordinate with slab forming, mechanical rough-ins and permitting. We’ll specify whether the house will be radon‑ready or will receive an active system, inspect the pre-pour vapor barrier and pipe rough-in, and verify fan installation, electrical hookup and visible manometer placement before final finishes. After construction we arrange post‑installation testing (short-term tests followed by or supplemented with longer-term testing if desired) and provide documentation for permits and closing. Installing mitigation during construction is less invasive and typically less expensive than retrofits, and it preserves interior finishes and layout flexibility while meeting local code and safety expectations.
How do I assess local radon risk and arrange pre-construction testing for my new custom home?
As a Denver custom home builder I always start by looking at local conditions before foundation work begins. Pull county radon-potential data and ask your builder for any recent test results from neighboring lots or houses in the same subdivision — geology can vary block-to-block in the Front Range. If your lot sits in a moderate-to-high risk area on local maps or if you plan a full or partial below-grade level, treat that as a prompt to budget for pre-construction testing so decisions can be made before the slab is poured.
For new construction the most useful tests are soil-gas samples and short-term continuous monitoring taken during excavation, not an indoor charcoal test after the house is finished. I recommend placing at least one probe near the future slab center and another near expected mechanical or garage openings; on larger lots add probes where soils or depth of fill change. A certified radon professional will either pull lab-analyzed soil-gas samples or run a continuous radon monitor for 48–72 hours under typical weather conditions — timing and stable barometric pressure matter to get representative results — and those numbers are what we use to determine whether mitigation planning is required.
Practical homeowner actions: require that pre-construction radon testing be included in your contract scope or as a specified allowance, insist on results documented in a lab-certified report with numeric concentrations, and make sure the builder coordinates scheduling so testing happens during excavation. Ask the builder to provide the testing professional’s certification (NRPP/AARST or equivalent) and a written recommendation based on the results; keep the report in your build folder so it’s available at closing and for future buyers.
Passive vs. active sub-slab depressurization planning (rough-in options)
Should I plan a passive or active sub-slab depressurization system when my custom home is being built? As a builder, we recommend treating the job as a “passive-first, active-ready” project: during slab/foundation work we rough in the components of a passive system (soil gas collection layer, pipe network and riser to the roof) because it’s low-cost and non‑disruptive, and it can be upgraded to an active system by simply adding a fan later if testing shows elevated radon. If you already know the site has high levels, tell us up front so we can rough-in for an active system immediately (dedicated wiring, fan location and structural support), which saves time and avoids rework.
What exact rough-ins should I ask the builder or GC to do? Ask for a continuous gas‑permeable layer under the slab (clean crushed rock or gas‑permeable membrane over a clean base) with a perforated collection pipe embedded in the aggregate tied to a central 3″–4″ Schedule 40 PVC riser. The riser should be routed in a straight run where possible, through a mechanical chase or up into the attic, and sleeved at roof or wall penetrations. Request a sealed slab penetration detail (gasket or sealed boot) and a permanent sampling/monitoring port at the riser base so post‑pour testing is straightforward.
How do I future‑proof the house for converting a passive system to active? Require a dedicated 120V circuit terminated to an accessible junction box near your planned fan location (attic, mechanical room or exterior wall) or run conduit from the attic to the electrical panel so adding a fan is a simple plug‑and‑connect job. Leave physical space and structural backing where the fan might mount, and ask us to label the riser and breaker in the panel. Finally, coordinate vent routing away from windows, doors and fresh‑air intakes and insist on vibration isolation and an accessible service location if the fan will be inside the building envelope to minimize noise and maintenance headaches.
Where will the radon pipes, fan, and other mitigation components be placed in my new custom home, and how do they integrate with the HVAC and structure?
From my experience building custom homes, a typical mitigation system uses 3″ or 4″ schedule‑40 PVC running from a suction point beneath the slab (or a collection sump) up through a framed chase to either the attic or an exterior wall. When planning pipe routing I aim for the straightest, shortest path with as few elbows as possible—every 90° elbow cuts airflow—so we often run the riser inside a closet or mechanical chase and then through the attic to the roof. All slab penetrations are sealed tightly with a poured patch or manufactured boot and the pipe joints are glued and strapped to the framing every 6–8 feet; this keeps the system airtight and serviceable for life of the house.
Choosing fan location is a homeowner decision I make with noise, maintenance access, and freeze protection in mind. Fans can be attic‑mounted, roof‑mounted, or exterior‑wall mounted; I usually prefer attic or exterior locations where the fan is accessible but isolated from living spaces. When the fan is in the attic we use a vibration isolator and a dedicated GFCI protected 120V circuit, and we size the fan to the planned piping—oversized fans waste energy, undersized fans can’t maintain suction. We also always provide a visible or electronic manometer or junction for a continuous monitor near a main living area so homeowners can quickly verify the system is operating.
Integration with the HVAC and structure is mostly about keeping systems separate but coordinated. Radon piping must not be tied into HVAC return or supply ducts; instead we route the riser clear of ductwork and avoid cutting structural members—when a chase must go through a joist or stud I pre‑plan headers or a sleeved opening so structural integrity isn’t compromised. We coordinate with the mechanical layout so the mitigation riser clears flues, bathroom vents, and attic insulation, and we terminate the pipe above the roofline with proper flashing and a weatherproof, animal‑resistant cap located away from soffit or operable openings to avoid re‑entry.
What building codes, permits, and post-installation tests are required for radon mitigation in new homes?
As an experienced custom home builder, I treat the radon mitigation permit and inspection process like any other code-driven system: you should expect a formal permit from your local building department and at least one plan review. Many jurisdictions require the mitigation system — including rough-in details — to be shown on the job drawings so the plan reviewer can confirm it meets local mechanical/electrical and roofing termination rules. That plan review typically references both your municipality’s code and recognized industry protocols for radon work, and the inspector will check the installation at rough-in and again at final before signing off.
After the system is operational, most places expect documented post-installation testing and a certificate of compliance. Practically speaking, you should get a written test report that states the test method, device used, start/end dates, and the measured radon level with the system running; jurisdictions often accept a short-term test (48–96 hours) for a final permit but many recommend or require a follow-up long-term test (months) to confirm performance over time. Be aware that some states use the EPA 4 pCi/L guideline while others have stricter thresholds, so ask your builder or mitigator what target your local inspectors use and what steps they’ll take if the system doesn’t bring levels below that target.
Before close or occupancy, insist on a simple documentation package from your builder/mitigator: a copy of the permit with inspection stamps, the installer’s license or certification, the final test report(s), and a labeled sticker on the system (model, serial number, install date). Also request clear owner instructions and warranty information so you know how to maintain the system and what triggers a contractor return visit. Keep these records with your home’s permanent file and use them in any future sale disclosure — they’re the proof that the system was installed to code and properly tested.
How much will radon mitigation cost, how do I choose the right contractor, and what warranties and maintenance should I expect?
As a builder who budgets radon control into new homes, expect lower installation costs when the system is roughed in during framing than when retrofitted later. In the Denver market a typical new-construction passive rough-in or simple active system usually falls roughly in the $800–$2,500 range depending on slab type, number of suction points, fan location (interior vs exterior), and how much conduit/electrical work is required; retrofits commonly run higher, often $1,200–$3,500 or more. Ask for an itemized bid that separates rough-in vs final fan installation, exterior penetrations, electrical work, and post-install testing so you can compare apples-to-apples and decide which items you want included in your construction budget versus as a later upgrade.
When choosing a contractor we look for credentials, local new-construction experience, and clear contracts. Require certifications from a recognized radon program, proof of insurance and references for jobs similar to yours, and a written scope that includes permits, post-install short-term or continuous testing, and a final certification showing levels below the action threshold. Insist that bids specify manufacturer and model of fans, expected fan life, who will provide the electrical connection, and an explicit performance guarantee — for example, a commitment to achieve radon below the EPA action level with defined corrective steps if levels remain high. Get the warranty in writing: manufacturers typically cover fans for several years (commonly 3–5 years), while contractor labor warranties vary; negotiate at least a one- to five-year labor warranty and confirm whether warranties transfer to future owners.
Homeowner-friendly maintenance and monitoring practices make the system reliable over the long term. We recommend commissioning testing after occupancy and again annually for the first two years, then every two to three years or after major foundation work; many homeowners also install a low-cost continuous monitor for peace of mind. Train the homeowner to visually inspect the pipe and fan monthly (listen for the fan hum, check for pipe damage, obstructions, or condensate), label the system location and breaker, and keep the contractor’s contact info in the homeowner manual. Plan for the eventual fan replacement — typical service life is roughly 10–15 years — and budget for a replacement fan plus labor (often a few hundred to under a thousand dollars depending on model and access).