A seller in Des Peres lists a home, assumes the sale will move like any other in West County, and waits for the city to schedule its walkthrough. The call never comes, because Des Peres doesn't make one. There's no occupancy inspection, no fire department sign-off, no certificate required before the keys change hands. Sellers sometimes read that as a clean pass. It isn't. It just means the one inspection that actually happens, the buyer's private one, carries all the weight the city inspection would have carried anywhere else. And in Des Peres, the item most likely to reopen a signed contract during that private inspection isn't the roof or the furnace. It's radon.
The City Isn't the Hurdle
Des Peres spells this out plainly on its own site: Des Peres does not require municipal/fire inspections for the sale of a residential home. No transfer inspection, no occupancy permit tied to the sale, no city inspector walking the property before closing.
That's not how it works everywhere in St. Louis County. According to the St. Louis chapter of the American Society of Home Inspectors, which tracks these rules municipality by municipality, Ballwin requires certification that a home complies with its housing code before it can be sold or occupied by a new resident. Berkeley requires an inspector's sign-off before anyone moves into a property. Black Jack requires an occupancy permit before move-in, full stop.
Sellers who've moved within the region, or who talk to friends selling in those cities, sometimes arrive in Des Peres expecting the same checkpoint. When it doesn't materialize, the instinct is relief. The better read is neutral. The city removed one gate. It didn't remove the transaction's risk, it just relocated it.
Where the Leverage Actually Sits
Every home sale in Missouri still goes through a private inspection, ordered by the buyer, paid for by the buyer, and used by the buyer's agent to build a repair or credit request. In cities with a mandatory municipal inspection, that city inspection often surfaces the small code items first, smoke detectors, GFCI outlets, handrails, so the private inspection's negotiating leverage gets split across two reports. In Des Peres, there's only one report, and it carries the full weight of whatever the buyer's inspector decides to flag.
This matters because the item most likely to show up on that single report, in this specific market, isn't cosmetic. It's a gas nobody can see or smell, and it doesn't care whether the city ever came by.
The Number the Building Department Never Checks
Missouri's Department of Health and Senior Services runs a statewide radon testing program, and its own data shows that 1 in 3 homes tested had indoor radon results that exceeded the recommended action level of 4.0 pCi/L. That's the level at which the EPA says a home should be fixed or mitigated. Regional radon contractors working in the metro area note that St. Louis falls into EPA Zone 2, with average indoor radon levels running above 3.0 pCi/L, a designation that reflects the region's underlying geology more than any single subdivision's build quality.
Missouri doesn't require any of this to be tested before a sale closes. The state is direct about it: there are no laws in Missouri that require radon testing or that require mitigation by the seller. What the state does say is that if a home already has a mitigation system installed, that system belongs on the Seller's Disclosure statement, so a buyer knows the house was flagged once already.
None of that removes radon from the negotiating table. It just means nobody is forcing the conversation to happen early. The buyer's inspector will order the test regardless of what the state or the city requires, because a radon reading above 4.0 pCi/L is exactly the kind of number that gives a buyer's agent grounds to ask for a price adjustment or a mitigation system before closing.
Why Des Peres's Own Age Works Against It
Radon risk isn't about how nice a house looks. It's about foundation type, soil contact, and how much of the structure sits below grade, which is another way of saying it's about age and construction style. Des Peres's own residential development history, published on the city's site, traces the pattern clearly. Postwar growth brought subdivisions like Harwood Hills, Berkley Manor, and Royal Acres. The 1970s added Dougherty Woods, Dougherty Lakes, and Four Winds Farm along Des Peres Road. By the city's own accounting, just over 25 percent of the housing units in Des Peres have been constructed since 1980, which means most of the city's homes predate that year.
Homes from that era in this part of Missouri were built with full basements far more often than not, and a basement is precisely the kind of foundation that gives soil gas the most direct path into a living space. A newer executive-style build on a similar lot might have a different foundation profile entirely. In Des Peres, the older half of the housing stock and the region's Zone 2 designation land on top of each other, which is exactly why a radon reading is a more live possibility here than the city's paperwork would ever suggest.
What This Actually Costs, In Real Numbers
When a buyer's inspection turns up an elevated reading, the sequence is fairly predictable:
- The buyer's inspector reports a result above 4.0 pCi/L.
- The buyer's agent requests either a mitigation system before closing or a price credit to cover one.
- The seller gets bids from an NRPP-certified contractor, since Missouri's health department recommends using a contractor certified through the National Radon Proficiency Program for anything tied to a real estate transaction.
- A mitigation system goes in, typically running $2,000 or less for a 2,000 square foot home, according to state guidance.
- Closing gets pushed, sometimes by a week or two, while the system is installed and, if the buyer wants confirmation, a follow-up test is run.
None of these steps are unusual on their own. What catches sellers off guard is the timing. Finding this out mid-contract, with a closing date already on the calendar, gives the seller far less room to shop contractors or negotiate the number than finding it out before the home ever goes on the market.
The Pre-Listing Move That Actually Changes the Negotiation
A seller who orders a radon test before listing controls the story. If the result comes back clean, that's a number worth having in hand when a buyer's inspector runs the same test later. If it comes back elevated, the seller gets to choose the contractor, get competing bids, and either install the system on their own timeline or price the home with the cost already factored in, rather than reacting to a buyer's demand under a contract deadline.
That's the real shape of selling in Des Peres. The city won't be the one asking questions. The buyer will, and the buyer's leverage is strongest when the seller hasn't looked first.
A Few Questions Worth Asking Before You List
Does Missouri require me to test for radon before selling my Des Peres home? No. The state has no law requiring testing or seller-side mitigation. The only disclosure requirement is that an existing mitigation system, if one is already installed, needs to be noted on the Seller's Disclosure statement.
If my buyer's inspection comes back above 4.0 pCi/L, am I obligated to fix it? Not automatically. It becomes a negotiation point, typically resolved through a mitigation system, a price credit, or in rare cases, a canceled contract if the parties can't agree.
Does the absence of a city inspection mean my home is less likely to have problems? No. Des Peres's exemption applies to municipal code items like smoke detectors, electrical, and general habitability. It has no bearing on radon, which is a soil-gas issue the city was never checking for in the first place.
If you're weighing a sale in Des Peres and want a clear read on what your specific home and lot are likely to face, from foundation type to timeline, Colleen and Team has spent decades pricing and preparing homes across this exact stretch of West County. Request Your Free Home Valuation and start the conversation with the full picture, not just the part the city checks.