Radon is an invisible, odorless radioactive gas that comes from uranium breakdown in soil and can enter new homes through foundation joints, utility penetrations, and porous concrete. In the Denver area and many parts of Colorado the natural geology produces elevated radon potential, so we treat radon risk as a routine part of site evaluation and construction planning. Testing and mitigation during the build phase is far more effective and cost-efficient than retrofits after occupancy, because it lets us install the necessary pathways and sealing while the foundation, slab, and mechanical spaces are exposed.
Our process begins during site evaluation and design: we review regional radon potential, coordinate any soil-gas testing you or a certified radon professional want performed after excavation, and then lay out mitigation components before the slab is poured. Typical construction‑phase testing options include on-site soil-gas measurements taken after excavation and final indoor testing once the house is weather-tight — short‑term electronic monitors (48–96 hours) give quick results and continuous monitors or long‑term detectors (alpha‑track) provide a seasonal average. We always work with licensed radon testers for post‑construction verification so readings are reliable for decision‑making and closing documentation.
Mitigation installed during construction is centered on a passive sub‑slab depressurization pathway that we integrate into the foundation: a gas‑permeable layer beneath the slab or under the crawlspace, collection piping that runs from beneath the slab up through the roof, sealed sump treatments, and careful sealing of utility penetrations and joints. We rough‑in electrical and conduit for a future fan so the system can be activated if post‑occupancy testing exceeds the EPA action level of 4 pCi/L. For homes with basements or walk‑out lower levels we design multiple suction points and larger collection piping as needed. By incorporating these measures into the build, RKM Homes minimizes cost and visual impact, simplifies future activation or fan installation, and documents performance with follow‑up testing before final handover.
How can I find my lot’s radon potential and what local codes or disclosure or permit requirements will affect radon work on my new custom home?
As a custom home builder in Denver, the first practical step I take is to pull the local radon potential information for the parcel before we finalize the design or bid. County and state radon maps give a risk classification that helps decide whether to include radon‑resistant details by default; however those maps are coarse and shouldn’t be the only input. Ask your builder to obtain the locality’s radon zone report and to file it in the project permit packet so you both have a documented starting point for decisions and for conversations with the building department.
Many jurisdictions reference the International Residential Code and its radon control provisions (and some local authorities adopt those provisions as mandatory or add their own requirements). That means a rough‑in or a passive radon system can be required on the foundation plans, may need a permit line item, and will often get inspected before the foundation is backfilled. Request that your construction plans explicitly show any radon rough‑ins and that the permit application cite the specific local code language so inspections are straightforward and you avoid costly rework later.
There are also disclosure and documentation expectations that affect new builds: sellers and builders typically must provide buyers with known testing or mitigation information and, in some states, specific radon disclosures at closing. From a practical standpoint, ask your builder to include language in the contract requiring documented radon steps (map/assessment, permited rough‑in, and final test results) and to deliver copies of permits and inspection sign‑offs at turnover. If the site shows elevated potential on the map, having that paperwork and a clear plan in the contract protects you and makes any future mitigation or disclosure during resale much simpler.
How and when should pre-construction soil‑gas testing be done for radon on my new custom home?
We schedule soil‑gas testing after rough grading and excavation for footings but before any slab work or compaction of the final subgrade — ideally at least 48 hours after heavy rain so the ground has stabilized. From our experience the most practical approach is to have a state‑ or nationally‑certified radon professional drive temporary soil probes to the planned slab depth (typically 3–6 feet) at several locations: a central probe, one at any known low or sump location, and extra probes where you have engineered fill or rockier conditions. For construction timelines we recommend continuous radon monitors (CRMs) attached to each probe for a 24–72 hour run so you capture short‑term variability (barometric and temperature swings) rather than relying on a single grab sample.
Interpreting soil‑gas numbers requires context: soil‑gas concentrations are usually orders of magnitude higher than what you’ll see indoors, so testers translate those results into risk for indoor levels. Use the EPA indoor action level of 4.0 pCi/L as the practical benchmark — if the professional indicates the soil‑gas pattern could reasonably drive indoor air above that level, plan for mitigation measures during construction. For borderline results we routinely install a passive rough‑in (vent pipe and sub‑slab access) so the house can be converted to an active system later without cutting the slab; when tests show consistently high or widely variable soil‑gas, we specify a mitigation design up front so the subcontractor can size suction points and routing correctly.
Practical next steps for homeowners: require the radon test in your construction schedule and contract so results arrive before slab crews mobilize, and ask for a written report showing probe locations, depths, raw data and a clear recommendation for whether a rough‑in or full mitigation is advised. Expect testing costs to run roughly $300–$1,200 depending on number of probes and whether CRMs are used — include a contingency in your budget for whatever mitigation the report recommends. Keeping the test report with your permit documents and disclosure paperwork saves money and surprises later, and it lets the builder coordinate mitigation work cleanly if it’s needed.
What radon‑resistant passive construction features should I include in my new custom home?
As a custom home builder I make the radon‑resistant details part of the slab prep so they’re efficient and invisible. For a slab‑on‑grade foundation that means a 4–6 inch clean crushed‑stone or pea‑gravel layer under the entire slab, and a continuous continuous PVC vent pipe stub bedded in that aggregate before the slab is poured. Over the aggregate I require a full‑coverage vapor/retarder sheet — I prefer a 10–12 mil reinforced polyethylene with all seams overlapped 12 inches and taped with a compatible butyl or acrylic tape — and I run that sheet up the foundation wall far enough to be sealed to the rough sill or stem wall so the slab edge is protected.
Sealing is where most builders lose performance, so I specify and inspect the details: all pipe, conduit and plumbing penetrations through the slab get factory grommets or are sealed with urethane caulk and a backer rod before concrete. Sump pits are installed with gas‑tight covers or sealed caps and sealed connections to the sub‑slab aggregate; control joints and the slab‑to‑stem wall interface are tooled and then caulked with a long‑life polyether or polyurethane sealant. I also seal around any post‑tension ducts, foundation drains, and utility chases and leave a labeled test port (a capped 1–1/2″ or 2″ port) accessible in the mechanical room so the passive system can be pressure tested or sampled later.
For a true radon‑ready rough‑in I route a 3″ (minimum) PVC riser from the aggregate bed up through the framing to an attic or through the roof, keeping the run vertical with as few turns as possible and securing it to framing to prevent movement. I locate the riser near the mechanical room so a future fan install is straightforward; the riser is capped and clearly labeled “RADON” and insulated where it passes through conditioned spaces to avoid condensation. When you review plans, ask me to show the riser path, vent termination location on the roof (kept away from windows and intake openings), and confirm you’ll get an accessible test port and documentation so a post‑construction radon test or fan installation is simple and low‑cost if needed.
What active radon mitigation system should I install and how will it be roughed‑in, installed, and tested during construction?
As an experienced custom home builder I recommend planning for a sub‑slab depressurization (SSD) system as the default active mitigation strategy when soil testing or local radon maps indicate any potential. SSD is the most common and reliable option for slab‑on‑grade and basements; for crawlspaces we use a sub‑membrane depressurization approach or sealed sump suction depending on the foundation type. Practically that means using 3‑inch PVC suction piping routed from collection points in the slab or from a sealed sump/drain tile area up through the framed wall into the attic or an exterior chase, locating the fan outside the conditioned envelope (attic, garage bump‑out, or an outside wall) for noise control, and terminating the exhaust well away from windows, doors and air intakes. I also specify a visible magnehelic or U‑tube manometer on the pipe so homeowners and service techs can quickly confirm the system is drawing a vacuum.
During rough‑in on site we pre‑position the suction ports or sump, run the vertical PVC riser to the chosen fan location, and install a labeled electrical outlet or dedicated circuit and an attic access panel where the fan will mount. If you want a fully active system at closing it’s best to install the fan and route the exhaust before drywall so bends and penetrations are minimized; otherwise a passive riser with a knockout for a future fan is cheap and unobtrusive. Commissioning consists of turning the fan on and observing the manometer to verify pressure change, then performing a short‑term radon test (commonly 48–72 hours with a continuous monitor or a certified test kit) placed in the lowest occupied level under closed‑house conditions — I request a live readout or lab report to document the “before/after” effect of the fan so any adjustments (extra suction points, higher capacity fan, or additional sealing) can be done before final turnover.
After the system is active the homeowner should keep it running 24/7 and have the installer provide the final test report, an as‑built drawing of pipe and suction locations, and simple maintenance instructions. Quick, practical homeowner checks are to note the manometer reading weekly for the first month, listen for unusual fan noise, and make sure the exterior discharge remains clear; fans typically last several years and are relatively easy to replace from the attic access point we install. If a follow‑up long‑term test is desired for insurance or peace of mind, do a 90‑day test once the house is occupied to confirm average exposure; insist that the mitigation contractor provides the test results and warranty documentation before final acceptance.
How do I find qualified radon contractors, which certifications matter, what are typical costs and warranties, and how is long‑term monitoring and maintenance handled?
From my experience as a custom home builder, start by requiring a mitigation contractor who carries a current radon credential (NRPP or NRSB certification are the most widely recognized) and any state‑level licensing where required. Ask for proof of general liability and workers’ compensation insurance, three recent new‑construction references, and copies of post‑installation test results they performed. When vetting bids, insist the proposal include the specific fan model, decibel rating, expected fan and pipe locations, and a simple as‑built sketch so you can compare apples‑to‑apples between contractors.
Expect lower incremental costs when a system is done during construction versus a retrofit: a passive rough‑in (pipe, membrane termination and chase) typically adds a few hundred dollars to framing costs, while a complete active system installed during construction commonly ranges roughly $900–$2,500 depending on fan choice and routing; complex foundations or multiple suction points can push costs higher. Require a written warranty in the contract: vendor fan warranty (usually 3–10 years), contractor workmanship warranty (commonly 1–5 years), and a performance clause that obligates the contractor to return and upgrade the system at no charge if post‑occupancy testing exceeds the agreed target (I recommend setting the remediation target to achieve below 4 pCi/L).
For long‑term performance, have the mitigation contractor install an accessible manometer or provide a plug‑in continuous monitor so the homeowner can verify the system is running; include a labeled service outlet and clear access to the fan so replacements are quick and inexpensive. Add post‑installation testing (short‑term followed by a confirmatory long‑term or two consecutive tests) to the project closeout checklist and specify who pays for follow‑up tests in the contract. Give the homeowner a one‑page maintenance sheet with expected fan life (typically 5–10 years), signs of failure (unusual noise, rising readings), recommended annual or biennial testing, and contact info for warranty service so the system remains effective for the life of the house.