Quick Answer: Loudoun & Fairfax Are Both High Risk in 2026
Quick Answer: Loudoun and Fairfax Counties are both high-risk for indoor radon in 2026 — Fairfax is EPA Zone 1 High with average 3.1 pCi/L and 24% of 23,192 tests at or above 4.0 pCi/L, Loudoun averages 4.1 pCi/L with 31% of 4,632 tests at or above 4.0 pCi/L and VDH says Loudoun should be re-designated from Moderate to High. EPA action level is 4.0 pCi/L — fix at or above, consider fixing at 2.0-3.9. The only way to know your home's level is to test the lowest livable level, especially basements in suburban DMV townhomes, condos, and small-lot detached in Ashburn, Sterling, Leesburg, Aldie, South Riding, Fairfax, Burke, and Centreville. Cost: $100-$200 professional, $4 VDH DIY kit, $15 hardware store short-term, mitigation $800-$1,200 typical sub-slab.
What Is Radon and pCi/L?
What is radon and how is it measured? Radon is a colorless, odorless radioactive gas from uranium decay in granite and shale soils common in Northern Virginia. Decay products are solids that stick to dust and lung tissue, emitting alpha particles. Measured in picocuries per liter pCi/L. Average US indoor ~1.3 pCi/L, outdoor ~0.4 pCi/L. EPA classifies risk as Zone 1 High >4 pCi/L potential, Zone 2 Moderate 2-4 pCi/L, Zone 3 Low <2 pCi/L. Virginia has 46 counties + 15 cities Zone 1, 24 counties + 8 cities Zone 2 per VDH Indoor Radon Program overview. Virginia Tech notes 15,000-22,000 US radon lung cancer deaths per year, ~700 per year in Virginia, second leading cause after smoking. You cannot smell or see radon, and allergic reactions are not a reliable indicator per VDH Real Estate Transactions briefing.
Fairfax vs Loudoun Radon Data and EPA Map Accuracy
Fairfax vs Loudoun radon data 2016-2024 and EPA map accuracy. Per VDH Real Estate Transactions table 1990-2017 Air Chek data and 2016-2024 tracking map, Fairfax County average 3.1 pCi/L with 23,192 tests and 24% >=4.0 pCi/L, designated High. Loudoun County average 4.1 pCi/L with 4,632 tests and 31% >=4.0 pCi/L, designated Moderate with asterisk. Prince William 2.9 pCi/L 3,487 tests 22% >=4 Moderate. VDH disclaimer on EPA Radon Risk Map for Virginia page developed 1993: map based on limited tests, geology, background radiation, never intended for predictive use. KNOWN INACCURACIES based on data since 1994: Loudoun County should be designated as high risk – not moderate. Low-risk I-95 corridor counties bordering high-risk to west should be moderate. High results found in every Virginia county including low-risk — homes built over small uranium deposits, non-native fill, or foundation cut into valleys/hillsides can spike. Generally closer to ocean lower odds but not guarantee. Testing data: Loudoun 31% high vs Fairfax 24% high means Loudoun basement owners should assume high-risk behavior even though old map shows orange moderate. USGS Map showing radon potential of rocks and soils in Fairfax County 1988 Miscellaneous Field Studies Map 2047 1:48,000 Otton et al. shows Fairfax geology variability — same lot can vary.
How to Test a Basement Correctly in VA
How to test a basement correctly in Virginia 2026 — VDH and ANSI/AARST protocol. Test the lowest livable level that is finished or could be finished — not crawlspaces, garages, cellars lacking utilities/headspace or exposed dirt/rock. In suburban DMV that is usually finished basement family room or bedroom. Place device at least 20 inches above floor, 3-6 feet breathing zone, away from outside walls, fans, windows, high-humidity bathrooms/laundry, sump pits, plumbing cut-outs, natural rock materials. Every section in contact with ground should be tested, especially different foundation types on different elevations. Closed-house conditions: all windows shut entire period, exterior doors normal entry/exit only, no whole-house exhaust fans or small fans near device, limit clothes dryer, maintain normal indoor temp. Start closed conditions 12 hours before test and maintain entire test minimum 48 hours — easier to run 60 hours and exclude first 12 hours if using continuous radon monitor CRM. Do not test during unusually severe storms — heavy precipitation, high sustained winds, powerful low pressure cause temporary high spikes. Short-term 2-7 days should not be during severe storm per VDH Testing page. For real estate, EPA recommends one short-term 48-hr minimum CRM test, or average of two short-term other tech, or one long-term 91-day minimum. CRM most popular $150-$250 professional, gives hourly readings plus temperature/barometric to detect tampering or storm. Long-term alpha track 91-day to 1-year most accurate — year-long considered gold standard. Digital real-time plug-in $125 not NRPP/NRSB approved for real estate — useful after mitigation monitoring only. Cost: professional $100-$200, DIY $15 hardware store, VDH $4 shipping vdhradon.org while supply lasts Oct-Apr free kit program. Devices must be NRSB or NRPP approved.
Mitigation Cost and Certified Pros
Radon mitigation, cost, and certified pros in Virginia. If result >=4.0 pCi/L EPA recommends fix, 2.0-3.9 consider fix, <2.0 optimal but not zero possible. Canada/EU action 5.4 pCi/L 200 Bq/m3, WHO recommends 2.7 pCi/L 100 Bq/m3. Mitigation: sealing cracks may help but usually pipe and fan sub-slab depressurization — removes gas below foundation before entry, no major remodel. Typical sub-slab $800-$1,200, crawl spaces or multi-section $2,000+ per VDH. Virginia Code 32.1-229.01 requires radon testers/mitigators be currently certified by NRSB or NRPP — search lists by zip code on nrsb.org or nrpp.info. Mitigators charging $1,000+ must hold VA Contractor's License, Radon Mitigation Contractor specialty after 5 years, licensed by DPOR. Follow ANSI/AARST standards MAH 2019, etc. via standards.aarst.org — VDH and EPA endorse though not yet in Code. Post-mitigation test required. Tamper-resistant techniques for seller-occupied: immobilize device, seller sign non-interference agreement, early drive-by visit, only certified placer/retriever. Seasonal note: highest levels winter, lowest summer, spring/fall near annual average, but clayish soils extended heat/drought can raise summer levels. Expect 25-50% reduction basement to first floor, smaller reductions upward, unusual pathways HVAC drawing from basement, utility chase, elevator shaft can raise upper floors.
Virginia Real Estate Law and Buyer Strategy
Virginia real estate law and what it means for buyers and sellers in Loudoun and Fairfax. No state or federal law requires radon testing before sale nor mitigation if elevated — entirely negotiable per VDH Real Estate Transactions slide 2019. Real estate contract may include radon test/mitigation contingency clause — ask your agent. VDH Office of Radiological Health investigates complaints against uncertified or noncompliant pros — need paperwork/photos, talk to pro first, then complaint to certificate provider NRSB/NRPP and BBB. For Loudoun and Fairfax suburban DMV framing — townhomes/condos/small-lot detached 1,500-3,000 sq ft in Ashburn Farm, Brambleton, Lansdowne, South Riding, Sterling, Leesburg, Aldie, Fairfax City, Burke Centre, Centreville — basements are common living space, home office, playroom, so testing lowest livable level matters for daily exposure. Appraisers and buyers do not price radon like granite — they price confidence. Pre-listing test with clean CRM report and closed-house log helps avoid day-10 renegotiation. For buyers, order radon with home inspection $100-$200, request 48-hr CRM, avoid testing during storm, and budget mitigation $800-$1,200 if needed. Search live Ashburn homes, Sterling homes, Leesburg homes, Fairfax homes, and Aldie homes via our Cities We Serve hub for basement inventory and walk-to-Metro filters. Text or call Cornerstone Realty Group at (571) 441-1031 for a 5-minute radon test map and mitigation referral — ★★★★★ 5.0 Verified only.
FAQ: Radon Tests in Northern VA
Sources & Next Step: VDH Indoor Radon Program vdh.virginia.gov/radiological-health/indoor-radon-program/ — EPA Radon Risk Map for Virginia with disclaimer and Known Inaccuracies Loudoun high risk, Fairfax high, 23,192 tests 24% >=4, 4,632 tests 31% >=4, VDH Radon Testing and Mitigation page closed-house protocol 20-inch rule every ground-contact section 48-hr min avoid severe storms CRM vs two short-term vs long-term 91-day $100-$200 pro $4 kit vdhradon.org, VDH Radon in Virginia Real Estate Transactions PDF Aug 2019 average table Augusta 5.0 41% High, Clarke 5.3 49% High, Fairfax 3.1 24% High, Frederick 7.2 45% High, Loudoun 4.1 31% Moderate asterisk should be High, Prince William 2.9 22% Moderate, action 4.0 mitigation 2-3.9 consider <2 optimal WHO 2.7 Canada 5.4, EPA Map of Radon Zones developed 1993 geology indoor measurements aerial radioactivity soil foundation not for home testing all homes test, USGS Map showing radon potential rocks and soils Fairfax County 1988 MF2047 1:48,000 Otton et al., Virginia Tech Radon invisible danger Jan 2025 15K-22K US deaths 700 VA $15 DIY $100-$200 pro $100-$200 long-term $100-$200 plug-in, VDH Radon Professionals page Virginia Code 32.1-229.01 NRSB NRPP certification required renewal 2 years ANSI/AARST standards. Text (571) 441-1031 for 5-min basement test referral and off-market Ashburn Farm Sterling Leesburg. Or search live homes below and get 3 values + 30 sales PDF at /home-valuation/ — ★★★★★ 5.0 team only. GA4 G-S6CE02DP9S and Meta Pixel 990042980225967 single-fire guard __cornerstoneTrackingInit intact.
FAQ
Is Loudoun County really high risk for radon even though the EPA map shows moderate?
Yes per VDH. EPA map 1993 shows Loudoun moderate orange, but VDH Known Inaccuracies note says Loudoun should be designated high risk based on 4,632 tests average 4.1 pCi/L 31% >=4.0 pCi/L vs Fairfax 3.1 pCi/L 24% >=4.0. Both counties have found high results in every Virginia county. VDH and EPA recommend testing all homes regardless of zone — especially those being purchased.
Where and how should I test my basement in Ashburn or Fairfax?
Test the lowest livable finished or finishable level — family room or bedroom — 20 inches off floor, 3-6 ft breathing zone, away from outside walls, sump, bathroom. Keep windows shut entire test plus 12 hours before, minimum 48 hours, ideally 60 hours to exclude first 12. Avoid severe storms. Test every ground-contact section. Professional CRM $150-$250 hourly log or VDH $4 kit vdhradon.org. Cost $100-$200 pro. Not crawlspace or garage lacking utilities.
What does radon mitigation cost in Virginia and do I need a licensed pro?
Typical sub-slab depressurization $800-$1,200, crawl or multi-section $2,000+ per VDH. Virginia Code 32.1-229.01 requires NRSB or NRPP certification to test or mitigate professionally, and $1,000+ jobs need VA Contractor License RMC specialty via DPOR. Mitigate at >=4.0 pCi/L, consider 2.0-3.9. Post-mitigation test required. Electronic plug-in $125 monitors are not approved for real estate transactions — use only after mitigation for tracking.