Radon in Armstrong County, Pennsylvania
Radon in Armstrong County: DEP-recorded basement tests average 10.76 pCi/L across 882 Armstrong County homes — nearly three times EPA's 4.0 pCi/L action level. First-floor readings average 5.31 pCi/L, above the action level on their own. Armstrong is the highest-reading county in its region. Every home here should be tested.
The 10.76 pCi/L Basement Average Is the Story
Armstrong County records a test-weighted basement average of 10.76 pCi/L across 882 PA DEP-recorded tests. EPA sets the action level for mitigation at 4.0 pCi/L. Armstrong sits at 2.69 times that threshold — not near it, not slightly over it, but almost three times above the number at which EPA tells homeowners to install a mitigation system.
The more consequential figure is the first floor. Armstrong first-floor tests average 5.31 pCi/L across 70 measurements. Basement averages above the action level are common across Pennsylvania; a first-floor average above 4.0 means the elevated soil gas is not staying below grade. In a home where the basement is finished, used as a bedroom, or connected to the living space by an open stair, the exposure is the exposure — there is no unoccupied buffer floor absorbing it.
The basement-to-first-floor ratio in Armstrong is 2.03. Radon concentration roughly halves as it moves up one floor, which is the ordinary pattern. What is not ordinary is the starting point: halving 10.76 still leaves a number above the action level.
Set against the rest of the Commonwealth, Armstrong ranks 15th of the 67 counties in the PA Radon Hub dataset by basement average, against a statewide test-weighted average of 6.44 pCi/L over 528,409 tests. Armstrong reads 67% above that statewide figure.
Why Armstrong Reads Higher Than Every County Around It
Armstrong shares county lines with six Pennsylvania counties, and it reads higher than all six. Jefferson averages 9.31 pCi/L, Butler 9.04, Clarion 8.46, Indiana 6.70, Westmoreland 5.93, and Allegheny 3.55. The swing from Armstrong to Allegheny across a single county line is a factor of three.
The underlying rock explains part of it. Armstrong sits on Appalachian Plateau bedrock — Allegheny River valley formations of Pennsylvanian sandstone and shale carrying elevated radium-226, the parent isotope that decays to radon. That is the same plateau section that runs beneath Allegheny County to the southwest, so the bedrock alone does not account for a three-fold difference in measured indoor radon.
Topography and housing depth do the rest. Kittanning, the county seat and the municipality carrying the county dataset, is built as a hillside-and-floodplain settlement along the Allegheny River. That pattern produces widely varying foundation depths across short distances — homes cut into a slope sit deeper into the weathered bedrock than homes on the terrace below, and depth into fractured rock is the strongest control on how much soil gas reaches a slab.
The housing stock is old and basement-heavy. The Census-reported median year built for owner-occupied housing in Armstrong County is 1960; in Kittanning borough itself it is 1946. Pre-1950 and mid-century construction in this region means block or poured basement walls with unsealed cold joints, floor drains, and no sub-slab vapor barrier — a full set of soil-gas entry points under a heated living space.
No Mitigation Firm Is Based in the County
The PA DEP Certified Mitigation Firms Directory lists zero DEP-certified mitigation firms with a business address in Armstrong County. Allegheny and Westmoreland each list five and Butler one. The practical consequence is scheduling: work in Armstrong is performed by certified professionals traveling in, which affects lead time more than it affects price.
That travel radius is why the county average matters to a homeowner here more than an individual anecdote does. With no local firm, there is no informal local knowledge circulating about which streets test high. The DEP dataset is the record, and it says the typical Armstrong basement is at 10.76 pCi/L.
Armstrong County homes carry a median owner-occupied value of $146,300 and, in the Kittanning area, a median sale price of $130,000. Buyers here commonly request radon testing during the inspection contingency window before closing. At a county average this far above the action level, a seller who has not tested is very likely to be negotiating a mitigation credit rather than a discretionary repair — which is an argument for testing before the listing goes up, not after an inspection report lands.
Measured Radon Data for Armstrong County
This unusually high reading may reflect a source data anomaly or a single-home outlier; individual home results vary widely.
Source: PA DEP RadonZip Tool, January 1990 – December 2025 · Updated 2026-05-20
Read the grid against the rest of the state. Armstrong is 15th of 67 counties by basement average in the PA Radon Hub dataset and 51st by test volume — a high reading on a comparatively small sample. The 882 basement tests all come from ZIP 16201, so this is a genuine measurement of the Kittanning area rather than a countywide census of every municipality in Armstrong.
That sample size also makes the peak reading worth handling carefully. A single 254.2 pCi/L result inside 882 tests pulls the county mean up by roughly 0.28 pCi/L on its own. Strip it out entirely and Armstrong still averages about 10.48 pCi/L — the anomaly is not what makes this county read high.
No DEP-certified mitigation firms are physically based in Armstrong County. Certified professionals from adjacent counties (Allegheny County (5 firms), Westmoreland County (5 firms), and Butler County (1 firm)) travel here to perform testing and mitigation.
Source: PA DEP Certified Mitigation Firms Directory, July 2026. This reflects business address only — firms based elsewhere may also serve Armstrong County.
Cities and Boroughs in Armstrong County
Kittanning carries the Armstrong County dataset. Its page holds the ZIP-level DEP averages behind the numbers above, the local mitigation cost range, and connections to DEP-certified professionals serving the county.
Adjacent Counties
Armstrong reads higher than all six counties it borders, and the drop-off is steep in every direction — from 9.31 pCi/L in Jefferson down to 3.55 pCi/L in Allegheny. If you are comparing a property here against one across a county line, these are the pages with the measured numbers.
Comparing radon risk across the wider Commonwealth? Browse All 67 Pennsylvania county radon pages for EPA zone classification and measured basement averages statewide.
Connect with a DEP-Certified Radon Professional
Submit your request and we will connect you with a DEP-certified professional serving Armstrong County. All providers verified against the PA Department of Environmental Protection Bureau of Radiation Protection directory.
(717) 461-2427Connect with a DEP-certified radon proPA Radon Hub is an independent informational resource. We do not perform radon testing or mitigation. We connect Pennsylvania property owners with independent, DEP-certified professionals — verify any contractor's certification at dep.pa.gov/radon before hiring.
Testing and Mitigation Options in Armstrong County
Where to Put the Detector in an Armstrong County Home
Test the lowest level you occupy or could plausibly finish. That is standard EPA guidance everywhere, but it carries extra weight in Armstrong because the first-floor average is already 5.31 pCi/L: a first-floor test here can return an actionable result on its own, which is not true in most Pennsylvania counties. Short-term charcoal canisters and continuous monitors run 48–96 hours at $15–$50. Long-term alpha-track detectors run 90 days or more and average out the heating-season stack effect that pushes winter readings above the annual mean.
What Mitigation Costs Here, and Why
Active sub-slab depressurization systems in the Kittanning area run $900–$2,200. Armstrong sits at the lower end of the statewide cost band because the dominant foundation type is a straightforward basement rather than a historic fieldstone or multi-level crawlspace assembly. High starting concentrations do not automatically mean an expensive system — they usually mean fan sizing and post-mitigation verification matter more, not that the installation is structurally harder.
Budget for the retest. A system that takes a 10.76 pCi/L starting point down to 2 pCi/L is doing more work than one starting at 4.5, and post-mitigation verification is the only thing that proves it got there.
Verifying an Out-of-County Contractor
Because no certified mitigation firm is based in Armstrong County, most contractors quoting work here will hold a business address in Allegheny, Butler, or another neighboring county. That is normal and permitted — certification under 25 Pa. Code § 240 is statewide, not county-scoped. Ask for the DEP certification number and confirm it is current before signing a contract or accepting payment.
Frequently Asked Questions
Why is the radon average in Armstrong County so high?
Armstrong County averages 10.76 pCi/L in basement tests — 2.69 times the EPA action level and 67% above the 6.44 pCi/L test-weighted average across the 67 counties in the PA Radon Hub dataset. Three factors combine: Appalachian Plateau bedrock of Pennsylvanian sandstone and shale carrying elevated radium-226; a hillside-and-floodplain settlement pattern along the Allegheny River that puts foundations at widely varying depths into weathered rock; and a basement-heavy housing stock with a county median year built of 1960 and a Kittanning borough median of 1946.
Is 10.76 pCi/L dangerous?
EPA sets 4.0 pCi/L as the level at which it recommends installing a mitigation system, so an average of 10.76 pCi/L is well into the range where EPA recommends action. That figure is a county-wide average of 882 measured tests, not a prediction for any individual property — some Armstrong homes test below 4.0 and some test far above. The only way to know a specific home's number is to test that home.
Do Armstrong County homes need testing if the basement is unfinished?
Yes. Armstrong first-floor tests average 5.31 pCi/L across 70 measurements, which is above the 4.0 pCi/L action level on its own. In most Pennsylvania counties the first-floor average sits below the action level and an unfinished basement acts as a buffer. That is not the case here. Test the lowest occupied level, and if the basement is unfinished, test the first floor as well.
How much does radon mitigation cost in Armstrong County?
Active sub-slab depressurization systems in the Kittanning area typically cost $900–$2,200 installed. Standard basement installations on poured-concrete foundations fall at the lower end; block-wall depressurization, multi-point suction, and crawlspace encapsulation push toward the upper end. A high starting concentration does not by itself raise the price — it raises the importance of correct fan sizing and of post-mitigation verification. All work must be performed by a DEP-certified mitigation professional under 25 Pa. Code § 240.
Are there DEP-certified radon contractors in Armstrong County?
The PA DEP Certified Mitigation Firms Directory lists no mitigation firms with a business address in Armstrong County. Certified professionals from neighboring counties — Allegheny and Westmoreland list five firms each, Butler one — travel here to perform testing and mitigation. DEP certification under 25 Pa. Code § 240 is statewide, so an out-of-county address is not a limitation; confirm the certification number is current before hiring.
Should I test before listing a home in Armstrong County?
Armstrong County buyers commonly request radon testing during the inspection contingency window before closing. With a county basement average of 10.76 pCi/L, the likely outcome of a buyer's test is an actionable result and a mitigation credit negotiated under time pressure. Pennsylvania's Real Estate Seller Disclosure Law (68 Pa.C.S. §§ 7301–7315) requires disclosure of known results but imposes no duty to test under § 7308 — so the decision to test before listing is a negotiating decision, not a legal one.
Which ZIP codes does the Armstrong County radon data cover?
The Armstrong County figures on this page aggregate ZIP code 16201, the Kittanning area — the ZCTA assigned to Kittanning in the Census 2020 ZCTA-to-Place relationship file and used for the PA DEP RadonZip Tool aggregation. All 882 basement tests and 70 first-floor tests behind the county averages come from that ZIP. Read the 10.76 pCi/L figure as a well-measured result for the Kittanning area rather than a census of every municipality in Armstrong County.
How does Armstrong County compare with the rest of Pennsylvania?
Armstrong ranks 15th of the 67 counties in the PA Radon Hub dataset by measured basement average, at 10.76 pCi/L against a statewide test-weighted average of 6.44 pCi/L across 528,409 tests. It is not the highest county in the Commonwealth — Potter County averages 16.29 pCi/L and Lebanon 14.02 — but it sits firmly in the upper quartile, and it is the highest-reading county in southwestern Pennsylvania among those it borders.
Related Reading
Independent resource — we do not perform testing. PA Radon Hub is an independent informational resource connecting Pennsylvania property owners with independent, DEP-certified radon professionals. We do not perform radon testing or mitigation. Verify contractor certification against the PA DEP Radon Services Directory before hiring.