Radon, Mold, Sewer Lines, and Other Colorado Inspection Add-Ons Worth Considering

A standard home inspection is thorough, but it’s also intentionally limited in scope. Several issues that can genuinely affect a home’s safety or your long-term costs fall outside a general inspector’s typical checklist, and radon in particular is a Colorado-specific issue worth taking seriously.

Radon Testing Isn’t Optional in Colorado, Statistically Speaking

The EPA classifies 52 to 53 of Colorado’s 64 counties as Zone 1, its highest radon risk category, and the Colorado Department of Public Health and Environment treats all 64 counties as high risk given widespread elevated test results. Nationally, only about 31 percent of counties fall into Zone 1. Colorado’s rate is more than 2.5 times the national average.

The practical impact is significant: roughly half of all tested homes in Colorado, and specifically in the Denver metro area, come back at or above the EPA’s action level of 4.0 picocuries per liter, based on CDPHE data covering more than 230,000 tests statewide. Radon forms as naturally occurring uranium in the region’s granitic bedrock decays, and the Front Range’s permeable, gravelly soils let the gas migrate easily into basements and crawlspaces.

Where Radon Tends to Run Even Higher

While every Denver metro county sits in Zone 1, some areas see particularly high test averages. Jefferson County, Golden, Lakewood, Littleton, and Evergreen among them, sees elevated levels due to its proximity to mountain bedrock. Douglas County’s granitic soils along the Palmer Divide, covering Castle Rock, Parker, and Highlands Ranch, show similarly high exceedance rates, as does Boulder County’s combination of foothills geology and alluvial soil. Arapahoe and Adams counties also see high rates, tied to the volume of basement construction over uranium-bearing soil in areas like Aurora, Centennial, and Thornton.

Testing Is Inexpensive Relative to the Stakes

A DIY radon test kit runs $15 to $30, and CDPHE offers discounted or free kits to Colorado residents. A professional test added to a standard home inspection typically costs $150 to $300. Real estate transactions typically use short-term testing, 2 to 7 days, with continuous radon monitors preferred specifically because they log hourly readings and can detect tampering. Long-term testing, 90 days to a year, captures seasonal variation, since radon levels tend to peak in winter when homes are sealed tightest, but it isn’t practical within a typical transaction timeline.

Colorado Law Now Requires Radon Disclosure

Under Senate Bill 23-206, effective since August 2023, Colorado sellers must provide buyers with a mandatory radon warning statement, any known radon test history or records, disclosure of whether a mitigation system exists on the property, and the current CDPHE educational brochure on radon, before a buyer becomes obligated under the purchase agreement.

Sewer Scope Inspections Matter More for Older Homes

A sewer scope inspection sends a small camera through the home’s main sewer line to check for cracks, root intrusion, or blockages, issues completely invisible during a standard inspection and potentially expensive to repair after closing. This is particularly worth considering for older homes, especially those with mature trees nearby, since root intrusion into aging sewer lines is one of the more common and costly issues a sewer scope catches early.

Mold Assessments Make Sense When There’s a Specific Reason to Look

A general home inspector may note visible signs of water damage or moisture, but a dedicated mold assessment goes further, testing air quality and identifying mold that isn’t visible to the naked eye. This is worth considering specifically when there’s a known history of water intrusion, a musty smell, or visible staining that raises a question the general inspection can’t fully answer.

A Few Other Add-Ons Worth Knowing About

A chimney inspection is easy to overlook but worth ordering for any home with a wood-burning fireplace, checking creosote buildup and structural condition that a general inspector typically doesn’t assess in detail. Pool and spa inspections make sense for exactly what they sound like, specialized equipment and safety checks outside a general inspector’s scope. Pest inspections matter most for older homes, visible wood damage, or anything flagged during the general inspection itself.

Deciding Which Add-Ons Are Actually Worth It

Given how high Colorado’s radon risk runs statewide, a radon test is worth treating as close to standard for any Colorado purchase, not an optional extra reserved for unusual circumstances. Sewer scopes and mold assessments are more situational, genuinely valuable for older homes or homes with a specific red flag, less necessary for new construction or homes with no relevant history.

Weighing the Cost Against What’s at Stake

Specialty inspections add real cost on top of the standard inspection, but they’re minor compared to what an undiscovered issue, elevated radon, a failing sewer line, hidden mold, can cost to address after you already own the home. For radon specifically, given how common elevated levels are here, the cost of testing is genuinely hard to justify skipping.

Frequently Asked Questions About Colorado Inspection Add-Ons

Is radon testing required when buying a home in Colorado?
It’s not mandatory, but sellers are required by law to disclose known radon information. Given that roughly half of tested Colorado homes exceed the EPA action level, testing is strongly recommended for any purchase.