Tygart Media

Tag: Property Damage

  • Radon Contractor Licensing Requirements by State: What You Need to Know

    The Distillery — Brew № 1 · Radon Mitigation

    Not all radon contractors are equally regulated. In some states, performing radon mitigation or measurement requires a state license — examination, insurance, continuing education, and annual renewal. In others, there is no requirement at all: anyone can install a radon system or conduct a radon test legally, regardless of training or competence. Knowing which type of state you live in is the first step toward protecting yourself when hiring.

    The Spectrum of State Radon Contractor Regulation

    State radon contractor requirements fall into several categories:

    States with Comprehensive State Licensing Programs

    These states have enacted radon-specific licensing statutes requiring contractors to obtain a state license to legally perform radon work. Licensing typically requires:

    • Passing a state examination or completing state-approved training
    • Demonstrating NRPP or NRSB national certification (some states accept national certification in lieu of a separate state exam)
    • Carrying general liability insurance and in some states E&O (errors and omissions) insurance
    • Paying a licensing fee and renewing annually or biennially
    • Completing continuing education during each license period

    States with comprehensive licensing programs (as of 2026) include: Florida, Illinois, Iowa, Kansas, Maine, Maryland, Minnesota, Montana, New Jersey, New York, Ohio, Pennsylvania, Tennessee, and others. Requirements change — verify current status with your state radon program.

    States That Accept National Certification as Licensing

    Some states do not have separate state licensing requirements but have enacted laws or regulations that require contractors to hold current NRPP or NRSB certification to perform radon work legally. The practical effect is similar to licensing — the national certification serves as the state qualification. States in this category include several that require certification for at least some types of radon work (real estate measurement, school testing, or mitigation work with homeowner contracts).

    States with No Radon Contractor Regulation

    Roughly half of U.S. states have no radon-specific contractor licensing or certification requirements. In these states, there is no legal barrier to anyone performing radon work — from installation of mitigation systems to conducting real estate radon tests — regardless of training or competence. This does not mean good contractors do not exist in these states; many voluntarily maintain NRPP or NRSB certification. But it means you cannot rely on legal licensing as a screening tool — you must verify credentials directly.

    Measurement vs. Mitigation Licensing: Different Requirements

    Many states regulate measurement and mitigation separately. A contractor may be licensed for one but not the other:

    • Measurement-only licensing: Required for conducting certified radon tests (particularly for real estate), even in states where mitigation has no licensing requirement
    • Mitigation-only licensing: Required for installing systems; the contractor may not be authorized to conduct certified post-mitigation measurements
    • Dual certification/licensing: Some professionals hold both; many do not — confirm which credential a professional holds before engaging them for a specific service

    How to Verify a Contractor’s State License

    • Your state health department radon program: The most authoritative source. State radon programs maintain lists of currently licensed contractors and often have an online lookup tool. Search for “[your state] radon program” or “[your state] radon contractor license”.
    • NRPP directory: nrpp.info — searchable by name, zip code, or certification number. Shows current certification status and discipline (measurement, mitigation, or both).
    • NRSB directory: nrsb.org — same search capability for NRSB-certified professionals.
    • Ask directly: Request the contractor’s state license number and national certification number. Ask which certification they hold (measurement, mitigation, or both). A legitimate professional provides this immediately.

    What “No State Licensing Requirement” Means in Practice

    In states without radon contractor regulation, your protection comes from:

    • Voluntarily certified contractors: NRPP and NRSB directories include contractors in unregulated states who have chosen to obtain and maintain national certification. Prioritize these contractors.
    • Contract terms: A written contract specifying that installation will follow AARST-ANSI SGM-SF requirements creates an enforceable standard even where licensing does not.
    • Workmanship warranty: Reputable contractors in unregulated states typically offer warranties equivalent to those required in licensed states. Get the warranty in writing before work begins.
    • Post-mitigation independent testing: Regardless of contractor certification status, placing your own post-mitigation test device independently confirms whether the system is achieving its purpose.

    Frequently Asked Questions

    Does my state require a licensed radon contractor?

    Approximately half of U.S. states require some form of radon contractor licensing or certification. The fastest way to find your state’s specific requirements is to search “[your state] radon program” through your state health or environment department website. Many state radon programs maintain a list of licensed contractors and post current requirements online. Requirements change — information that is two or more years old may be outdated.

    Can an unlicensed contractor install a radon system?

    In states without radon contractor licensing requirements, yes — legally. In states with licensing requirements, performing radon mitigation without a license is illegal and may void warranty coverage, create liability for the homeowner (if work requires a building permit), and result in a system that does not meet AARST-ANSI standards. Always verify your state’s requirements and the contractor’s credentials before engaging anyone for radon work.

    Does a radon contractor need to be licensed to test and mitigate?

    Often yes for both activities — but through separate credentials. In most states with licensing, measurement (testing) and mitigation (system installation) are separately licensed or certified. A contractor licensed only for mitigation may not be authorized to conduct the certified post-mitigation measurement. Verify both credentials when a single contractor proposes to both install and certify the post-installation result.

  • AARST-ANSI Radon Standards: What They Are and Why They Matter

    The Distillery — Brew № 1 · Radon Mitigation

    When a radon professional says they follow “AARST standards,” they are referring to a specific set of American National Standards developed by the American Association of Radon Scientists and Technologists (AARST) and approved by the American National Standards Institute (ANSI). These standards are the technical backbone of professional radon practice in the United States — governing how systems are installed, how measurements are conducted, and what constitutes acceptable post-mitigation performance. Understanding what these standards require helps you evaluate whether a contractor is following best practice or cutting corners.

    What Is AARST?

    The American Association of Radon Scientists and Technologists (AARST) is the primary professional organization for radon professionals in the United States. Founded in 1988 — the same year as the Indoor Radon Abatement Act — AARST administers the National Radon Proficiency Program (NRPP), develops technical standards through a consensus process, and advocates for radon-related policy. AARST’s standards are developed collaboratively by measurement professionals, mitigators, researchers, regulators, and public health specialists.

    What Is ANSI Approval?

    The American National Standards Institute (ANSI) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, and systems in the United States. ANSI accreditation ensures that standards are developed through a documented, consensus-based process with balanced stakeholder representation and opportunities for public comment. AARST’s key radon standards are ANSI-approved, meaning they carry the authority of the U.S. voluntary consensus standards system — the same system that produces ASTM, ASHRAE, and ASME standards used throughout U.S. construction and engineering.

    The Core AARST-ANSI Radon Standards

    ANSI/AARST SGM-SF: Mitigation Standard for Single-Family Homes

    Standard of Practice for Mitigation of Radon in Schools and Large Buildings — Single-Family (SGM-SF) is the governing standard for radon mitigation system design and installation in single-family residential buildings. This is the standard that determines:

    • Required pre-installation diagnostic testing procedures
    • Fan placement requirements (unconditioned space only)
    • Pipe sizing, routing, and joint cementing requirements
    • Slab sealing requirements
    • System performance indicator (manometer) requirements
    • Required labeling on installed systems
    • Post-installation testing timing and protocol
    • Documentation requirements for installed systems

    SGM-SF is referenced in NRPP certification requirements and is the standard against which certified Radon Mitigation Specialists are tested. Many state radon programs and contractor licensing requirements specifically cite SGM-SF compliance as a requirement for licensed work.

    ANSI/AARST RMS-LB: Mitigation Standard for Large Buildings

    The Radon Mitigation Standard for Large Buildings (RMS-LB) covers radon mitigation in schools, commercial buildings, multifamily housing, and other large structures. It addresses the additional complexity of large-building mitigation: multiple foundation zones, complex HVAC integration, sub-membrane depressurization for large crawl spaces, and the heightened documentation and verification requirements appropriate for public-use buildings.

    ANSI/AARST MAMF: Measurement Standard for Multi-Family and Large Buildings

    The Measurement and Mitigation Protocol for Large Buildings (MAMF) governs radon measurement in commercial and multifamily residential settings. For real estate professionals, the most relevant application is its guidance on certified measurement for real estate transactions — particularly in multifamily and commercial properties where residential measurement standards (which address single-family protocol) may not directly apply.

    ANSI/AARST RRNC-2022: Radon-Resistant New Construction Standard

    The Radon-Resistant New Construction standard (RRNC-2022) defines the technical requirements for incorporating radon-resistant features into new residential construction. It is the most current and comprehensive technical document governing RRNC — superseding earlier EPA guidance documents on the topic. Key content includes:

    • Gas-permeable layer specifications (aggregate type, depth, coverage)
    • Vapor barrier specifications (minimum thickness, seam overlap, sealing requirements)
    • Vent pipe specifications (diameter, schedule, routing, termination)
    • Electrical outlet requirements for future fan activation
    • Crawl space-specific RRNC provisions
    • Quality verification requirements

    ANSI/AARST Series SSDS: Soil Suction Depressurization Standards

    The SSDS series covers specific mitigation methods including sub-slab depressurization, sub-membrane depressurization, drain-tile depressurization, and block-wall depressurization — providing technical specifications for each method type that exceed the general requirements in SGM-SF.

    How Standards Are Used in Practice

    AARST-ANSI standards function as the technical reference layer for radon professional practice in several ways:

    • Certification examinations: NRPP and NRSB certification exams test knowledge of AARST-ANSI standards — a certified professional is expected to know and follow these requirements
    • State licensing requirements: States with radon contractor licensing often cite AARST-ANSI standards as the technical basis for licensed work — contractors must demonstrate compliance
    • Workmanship warranty basis: When a mitigator’s workmanship warranty specifies what they will and will not do on a callback, the underlying technical obligation is typically SGM-SF compliance
    • Litigation reference: In disputes about radon mitigation quality or post-mitigation testing results, AARST-ANSI standards provide the objective technical benchmark against which contractor work is evaluated
    • Real estate due diligence: Buyers and home inspectors can reference AARST-ANSI standards to evaluate whether an existing mitigation system was installed to professional standards

    Frequently Asked Questions

    Are AARST-ANSI radon standards legally binding?

    AARST-ANSI standards are voluntary consensus standards — they are not automatically law. However, they become legally operative when incorporated by reference into state licensing requirements, building codes, or contract specifications. When a state radon licensing law requires compliance with SGM-SF, that standard becomes legally binding in that state. When a contractor’s contract specifies AARST-ANSI standard compliance, violation becomes a breach of contract. Courts also routinely treat industry consensus standards as evidence of the duty of care applicable to professionals in negligence cases.

    How do I know if my mitigation contractor followed AARST standards?

    Key SGM-SF compliance indicators to check: fan is in unconditioned space (attic, exterior, or garage — not a finished basement or utility room); all PVC joints are cemented (not dry-fitted); a U-tube manometer is installed and visible; required warning label is on the pipe; slab core hole is sealed with hydraulic cement (not just foam); and the contractor provided written documentation of pre-mitigation radon level, system specifications, and post-mitigation test results. A system missing any of these elements is likely not fully SGM-SF compliant.

    Where can I get copies of AARST-ANSI radon standards?

    AARST-ANSI standards are available for purchase through the AARST website (aarst.org) and through the ANSI standards store (ansi.org). Some standards are available for free download from AARST as part of their public education mission. State radon programs sometimes make the most relevant standard (typically SGM-SF) available as a reference document.

  • EPA Radon Zone Map: What Zone 1, 2, and 3 Mean for Your Home

    The Distillery — Brew № 1 · Radon Mitigation

    EPA’s Map of Radon Zones divides every U.S. county into one of three zones based on predicted average indoor radon levels. The map is widely cited in radon regulations, building codes, and HUD requirements — but it is frequently misunderstood. Zone designation does not tell you your home’s radon level. It tells you the predicted average for your county, which may have little bearing on the specific geology beneath your foundation.

    The Three Radon Zones

    Zone 1: Highest Potential (Predicted Average Above 4.0 pCi/L)

    Zone 1 counties have the highest predicted indoor radon potential. EPA’s methodology predicts that the average indoor radon level in Zone 1 counties exceeds the EPA action level of 4.0 pCi/L. Zone 1 counties are concentrated in the Northern Plains, Rocky Mountain states, Pennsylvania, Ohio, Iowa, and parts of the mid-Atlantic — regions with uranium-rich geology including granite formations, black shale, and glacial deposits.

    Zone 1 status triggers several regulatory consequences:

    • HUD requires radon testing for federally assisted multifamily housing in Zone 1 counties
    • Some states mandate RRNC (Radon-Resistant New Construction) for residential construction in Zone 1 counties
    • EPA recommends RRNC for all new construction in Zone 1 regardless of state requirements
    • Some states with school radon testing mandates prioritize Zone 1 districts

    Zone 2: Moderate Potential (Predicted Average 2.0–4.0 pCi/L)

    Zone 2 counties have predicted average indoor radon levels between the EPA “consider mitigating” level (2.0 pCi/L) and the action level (4.0 pCi/L). Zone 2 represents a substantial portion of U.S. counties. EPA still recommends testing in Zone 2 and recommends RRNC for new construction — the lower priority relative to Zone 1 reflects statistical averages, not safety.

    Zone 3: Lowest Potential (Predicted Average Below 2.0 pCi/L)

    Zone 3 counties have the lowest predicted radon potential. The average predicted indoor level is below 2.0 pCi/L. EPA still recommends testing in Zone 3 — individual homes in Zone 3 counties can and do have elevated radon due to local geology, soil conditions, and construction variations. “Low-radon zone” does not mean “radon-free zone.”

    How the Zone Map Was Developed

    EPA published the original Radon Zone Map in 1993 based on data from three sources:

    • Indoor radon surveys: State radon measurement data from the EPA/State Residential Radon Survey conducted in the late 1980s, providing actual indoor radon measurements from thousands of homes across the country
    • Aerial radiometric surveys: U.S. Geological Survey (USGS) airborne gamma-ray data measuring surface uranium, thorium, and potassium concentrations — proxies for radon-producing geology
    • Geology: USGS geologic map data identifying rock and soil types with known radon-producing potential

    These three data layers were combined at the county level to produce the zone assignments. The map has not been substantially revised since 1993, despite significant improvements in radon testing data availability. Some researchers have noted that the 1993 map may underpredict Zone 1 designation in certain geologic regions based on more recent measurement data.

    Critical Limitation: County Averages vs. Individual Homes

    The most important thing to understand about the radon zone map is what it cannot tell you: your home’s actual radon level. The map assigns zones based on county-level averages. Within any county — including Zone 3 counties — individual homes can vary from 0.2 pCi/L to 50+ pCi/L depending on:

    • Local soil type and permeability (sandy soils allow faster radon movement than clay)
    • Local bedrock uranium content (a single granitic intrusion can elevate radon in a small cluster of homes surrounded by low-radon geology)
    • Foundation type and construction quality (slab vs. basement vs. crawl space; sealed vs. cracked)
    • Building pressure dynamics (stack effect, HVAC, ventilation rate)
    • Proximity to the water table and seasonal moisture levels

    EPA’s own guidance explicitly states: “Any home can have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements.” Zone designation is a statistical predictor of regional risk, not a predictor of individual home risk.

    How to Find Your County’s Radon Zone

    EPA’s radon zone map is available at epa.gov/radon/find-information-about-local-radon-zones-and-state-contact-information. The map is searchable by state, and each state’s zone assignments are listed by county. The EPA also links to state-specific radon contact information, which often includes more detailed local radon data than the federal county-level map.

    Many state radon programs publish sub-county radon data — zip code level or census tract level — that provides more precise local risk information than the EPA’s county-level map. For the most accurate local picture, consult your state radon program’s data in addition to the EPA map.

    Frequently Asked Questions

    Does living in a Zone 3 county mean I don’t need to test for radon?

    No. Zone 3 means your county has the lowest predicted average radon potential nationally — it does not mean individual homes in your county are free of radon risk. EPA recommends testing in all zones. Significant local radon elevations occur in Zone 3 counties due to localized geology, soil conditions, and construction factors that the county-level map cannot capture.

    Is the EPA radon zone map accurate?

    The map is accurate as a statistical predictor of county-level averages based on 1993 data — which was the best available methodology at the time. It is not accurate as a predictor of individual home radon levels. The map’s limitations are well-documented in the literature: some counties are misclassified relative to more recent measurement data, and county-level averaging obscures significant within-county variation. Use it as context, not as a substitute for testing.

    What does Zone 1 mean for new construction?

    EPA recommends RRNC (Radon-Resistant New Construction) for all new homes in Zone 1 counties. Some states mandate RRNC for Zone 1 construction regardless of whether the specific site has been tested. HUD requires radon testing and mitigation for federally assisted multifamily projects in Zone 1. Even where not mandated, RRNC is strongly advisable in Zone 1 — the cost during construction ($350–$700) is a fraction of post-construction remediation ($800–$2,500).

  • Radon Regulations in the United States: Federal, State, and Local Overview

    The Distillery — Brew № 1 · Radon Mitigation

    The United States does not have a single federal radon law. Instead, radon regulation in America is a patchwork of federal guidelines, state licensing and disclosure laws, building code requirements, and voluntary programs — each operating independently. Understanding this structure explains why radon requirements differ dramatically between states, why some transactions require certified professionals while others do not, and why “federal radon law” is largely a misnomer.

    Federal Radon Framework: Guidelines, Not Mandates

    At the federal level, the EPA is the primary radon authority. The EPA’s radon program operates almost entirely through guidance, technical assistance, and voluntary programs — not regulatory mandates. Two federal statutes form the legal foundation:

    Indoor Radon Abatement Act (IRAA) of 1988

    The Indoor Radon Abatement Act, enacted as Title III of the Toxic Substances Control Act (TSCA), established the federal policy framework for radon. Key provisions:

    • Declared that the national long-term goal is reducing indoor radon to outdoor levels (~0.4 pCi/L)
    • Directed EPA to publish technical guidance and establish a radon measurement proficiency program
    • Authorized grants to states for radon programs, technical assistance, and public education
    • Directed EPA to develop model construction standards for radon-resistant new construction
    • Did not establish mandatory testing requirements, mandatory action levels, or federal licensing requirements for contractors

    Residential Lead-Based Paint Hazard Reduction Act of 1992 (Title X)

    Title X of the Housing and Community Development Act included radon provisions affecting federally assisted housing. It directed HUD to develop radon testing and mitigation requirements for HUD-assisted housing in high-radon areas and required disclosure of known radon hazards in federally assisted housing transactions.

    EPA’s Role: Guidance Authority

    EPA’s primary radon tools are guidance documents, technical standards, and voluntary programs:

    • EPA Action Level (4.0 pCi/L): EPA’s recommended action level for mitigation. It is a guidance value, not a regulatory standard — there is no federal penalty for having a home above 4.0 pCi/L, and no federal requirement to test or mitigate.
    • EPA Radon Measurement Proficiency (RMP) Program: Established the original framework for certifying radon measurement professionals. Now administered through NRPP (AARST) and NRSB as independent certification bodies.
    • State Indoor Radon Grants (SIRG): EPA provides annual grants to state radon programs under IRAA. These grants fund state testing programs, contractor certification, public outreach, and radon-resistant new construction promotion.
    • Radon Zone Map: EPA’s Map of Radon Zones designates all U.S. counties as Zone 1 (highest potential, predicted average above 4.0 pCi/L), Zone 2 (moderate, 2.0–4.0 pCi/L), or Zone 3 (lowest potential, below 2.0 pCi/L). The map informs but does not compel action.

    State Authority: Where Regulation Actually Happens

    States are the primary regulatory actors in radon. Through their police powers over public health, states have enacted a wide range of radon-specific laws:

    Contractor Licensing

    Approximately 20+ states require radon professionals to hold a state license or certification to legally conduct radon measurement or mitigation. Requirements vary significantly:

    • Some states (e.g., New Jersey, Pennsylvania, Florida) have comprehensive licensing programs with examination, continuing education, and liability insurance requirements
    • Some states accept NRPP or NRSB national certification as sufficient
    • Some states require state-specific licensing in addition to national certification
    • States without licensing requirements allow anyone to conduct radon work — no examination or certification needed

    Real Estate Disclosure

    Many states have enacted radon disclosure requirements for real estate transactions. Common structures:

    • Known results disclosure: Sellers must disclose any known radon test results (Florida, Illinois, Maine, and others)
    • Mitigation system disclosure: Sellers must disclose the presence of an existing radon mitigation system
    • EPA pamphlet distribution: Some states require providing the EPA “Home Buyer’s and Seller’s Guide to Radon” to buyers
    • No specific radon disclosure law: The general material defect disclosure duty under real estate law may cover known elevated radon in most states even without a specific radon statute

    School and Public Building Requirements

    Illinois, New Jersey, Pennsylvania, and several other states require radon testing in schools and/or childcare facilities. Requirements differ in frequency, action levels, and who conducts testing.

    Rental Property Requirements

    Some states with high radon prevalence have enacted landlord disclosure or testing requirements for rental properties. These are typically narrower in scope than homeowner requirements and vary substantially between states.

    Building Codes: The RRNC Adoption Map

    Radon-Resistant New Construction (RRNC) is addressed in the International Residential Code (IRC), which most U.S. jurisdictions have adopted in some form. The IRC includes an appendix (Appendix F) with RRNC requirements — but appendices are optional, and adoption varies by state and locality:

    • Some states mandate IRC Appendix F adoption statewide for high-radon counties
    • Some counties and municipalities in non-mandating states have adopted RRNC locally
    • Many jurisdictions have adopted the IRC base code but not the RRNC appendix — RRNC is not required even though a general building code exists

    States with statewide RRNC mandates or strong local adoption include portions of Colorado, Iowa, Maryland, Minnesota, Montana, North Dakota, and South Dakota — all Zone 1 states. Even in these states, enforcement varies by jurisdiction.

    HUD and Federally Assisted Housing

    The U.S. Department of Housing and Urban Development (HUD) has established radon requirements for multifamily housing projects receiving federal assistance. HUD’s Office of Lead Hazard Control and Healthy Homes (OLHCHH) administers radon policy for HUD-assisted properties:

    • Properties in EPA Zone 1 counties receiving certain HUD assistance must test for radon
    • Properties exceeding 4.0 pCi/L must mitigate before or shortly after occupancy
    • New HUD-assisted multifamily construction in Zone 1 must incorporate RRNC features

    Frequently Asked Questions

    Is there a federal law requiring radon testing in homes?

    No. The Indoor Radon Abatement Act of 1988 established federal radon policy and directed EPA to develop guidance and voluntary programs, but it does not mandate testing in private residences. Radon testing requirements for homeowners, if any, come from state law — and most states do not mandate testing in owner-occupied residences.

    Which level of government regulates radon contractors?

    States regulate radon contractors. There is no federal radon contractor licensing requirement. Approximately 20+ states require state licensing or accept national certification (NRPP or NRSB) for radon measurement and/or mitigation work. In states without contractor regulation, anyone can legally perform radon work regardless of training.

    Does EPA set legally binding radon limits?

    No. EPA’s 4.0 pCi/L action level is a guidance recommendation, not a legally binding regulatory standard. There is no federal penalty for radon levels above 4.0 pCi/L in a private residence, no federal requirement to remediate, and no federal enforcement mechanism for residential radon. The action level guides voluntary decisions and state programs, but it is not a regulatory threshold with legal consequences in the same way that OSHA exposure limits or EPA ambient air standards are.

  • Radon Units Explained: pCi/L vs. Bq/m³ vs. WL

    The Distillery — Brew № 1 · Radon Mitigation

    If you have ever researched radon internationally, you may have encountered test results or guidelines expressed in units that look unfamiliar — Bq/m³ from European sources, WL from occupational health documents, or pCi/L from U.S. EPA guidance. All three measure the same phenomenon (radon radioactivity in air) but express it differently. Understanding the conversions and the context in which each unit is used lets you compare international research, interpret older documents, and understand why your neighbor’s European renovation report quotes a different number than your EPA-sourced action level.

    picocuries per liter (pCi/L) — The U.S. Standard

    The picocurie per liter is the standard unit for radon concentration in air used by the U.S. EPA, U.S. state radon programs, and most North American regulatory frameworks.

    What It Measures

    A curie (Ci) is a unit of radioactivity equal to 37 billion disintegrations per second — defined as the activity of one gram of radium-226. A picocurie (pCi) is one trillionth of a curie, or 0.037 disintegrations per second. Picocuries per liter expresses how many radon disintegrations per second are occurring in one liter of air.

    At EPA’s action level of 4.0 pCi/L, approximately 0.148 radon disintegrations occur per second per liter of air in your home — or about 9 per minute per liter.

    Key Reference Values in pCi/L

    • Outdoor average (U.S.): ~0.4 pCi/L
    • Indoor average (U.S.): ~1.3 pCi/L
    • EPA “consider mitigating” level: 2.0 pCi/L
    • EPA action level: 4.0 pCi/L
    • EPA “fix immediately” level: 8.0 pCi/L (or higher — no waiting for confirmatory test)

    becquerels per cubic meter (Bq/m³) — The International Standard

    The becquerel per cubic meter is the SI (International System of Units) standard for radon concentration. It is used by the World Health Organization, European Union radon regulations, and most countries outside North America.

    What It Measures

    A becquerel (Bq) is one radioactive disintegration per second. Becquerels per cubic meter (Bq/m³) expresses how many radon disintegrations per second occur in one cubic meter of air. Because 1 cubic meter = 1,000 liters, the conversion between Bq/m³ and pCi/L involves both the volume conversion and the unit conversion.

    Conversion Formula

    1 pCi/L = 37 Bq/m³ (exact conversion)
    1 Bq/m³ = 0.027 pCi/L

    Practical conversions:

    • EPA action level (4.0 pCi/L) = 148 Bq/m³
    • WHO reference level (100 Bq/m³) = 2.7 pCi/L
    • EU reference level (300 Bq/m³ for existing buildings) = 8.1 pCi/L
    • EU reference level (200 Bq/m³ for new construction) = 5.4 pCi/L

    Key Reference Values in Bq/m³

    • Outdoor average: ~15 Bq/m³
    • Indoor average (U.S.): ~48 Bq/m³
    • WHO reference level: 100 Bq/m³ (2.7 pCi/L)
    • EU reference level (existing buildings): 300 Bq/m³ (8.1 pCi/L)

    Working Levels (WL) — The Occupational Standard

    The working level (WL) is an older unit developed for measuring radon exposure in uranium mines and other occupational settings. It measures the combined energy of all short-lived radon decay products (progeny) in one liter of air — not radon itself. It remains in use in some occupational health, regulatory, and older literature contexts, but is rarely used in modern residential radon programs.

    What It Measures

    One working level (1 WL) is defined as any combination of short-lived radon progeny in one liter of air that will result in the emission of 1.3 × 10⁵ MeV of alpha energy upon complete decay. At equilibrium between radon and its progeny, 1 WL corresponds to approximately 200 pCi/L of radon.

    Conversion Formula

    At typical indoor equilibrium ratios (approximately 0.4 equilibrium factor):
    1 WL ≈ 200 pCi/L of radon (at complete equilibrium)
    EPA’s 4.0 pCi/L action level ≈ 0.02 WL

    Working level months (WLM) is the cumulative exposure metric — one WLM equals exposure to 1 WL for one working month (170 hours). Occupational exposure limits and mining health regulations are often expressed in WLM per year.

    Quick Conversion Reference

    pCi/LBq/m³WL (approx.)Context
    0.4150.002Outdoor average
    1.3480.007U.S. indoor average
    2.71000.014WHO reference level
    4.01480.02EPA action level
    8.02960.04EPA immediate action
    8.13000.04EU reference level (existing buildings)
    20.07400.1High-risk residential

    Frequently Asked Questions

    Why does the WHO action level seem lower than EPA’s?

    The WHO reference level of 100 Bq/m³ (2.7 pCi/L) is lower than EPA’s 4.0 pCi/L (148 Bq/m³) because the WHO chose to set a more conservative reference level reflecting updated health evidence. EPA’s 4.0 pCi/L level was set in the 1980s and has not been formally revised, though EPA acknowledges that radon between 2.0 and 4.0 pCi/L still poses meaningful risk and recommends considering mitigation in that range.

    If my test result is in Bq/m³, how do I know if I should mitigate?

    Divide your Bq/m³ result by 37 to get the pCi/L equivalent. If the result is 148 Bq/m³ or higher (4.0 pCi/L), EPA recommends mitigation. If you are following WHO guidance, the reference level is 100 Bq/m³ (2.7 pCi/L). If following EU guidance for existing buildings, the reference level is 300 Bq/m³ (8.1 pCi/L).

    My old test report shows results in WL — how do I convert to pCi/L?

    Multiply the WL value by 200 to get the approximate equivalent pCi/L at complete equilibrium. For example, 0.02 WL × 200 = 4.0 pCi/L. Because actual indoor equilibrium factors vary (typically 0.3–0.5, not 1.0), WL-to-pCi/L conversions have some inherent uncertainty. For modern residential decisions, use pCi/L or Bq/m³ from a current lab test.

  • Radon Testing for Schools and Daycares: EPA Guidelines and AARST Standards

    The Distillery — Brew № 1 · Radon Mitigation

    Children spend 6–8 hours per day in schools and daycares — second only to their homes in daily occupancy time. Because radon exposure risk is cumulative and children’s developing lungs may be more sensitive to radiation, radon in school buildings is a significant public health concern. EPA has published specific guidelines for school radon testing, and AARST-ANSI has developed standards (SGM-SF) that govern professional testing in educational and large commercial buildings.

    Why Schools Are a Priority

    School buildings face the same radon entry pathways as residences — soil gas entering through foundation cracks, floor penetrations, slab joints, and block wall cavities. Several factors make schools a particular concern:

    • Long daily occupancy by vulnerable populations: Children spend 1,000+ hours per year in school buildings. Cumulative radon exposure during childhood contributes to lifetime lung cancer risk.
    • Ground-floor and below-grade classrooms: Many schools have ground-floor or basement classrooms — the highest-radon zones in any building.
    • Large building volumes: Large buildings dilute radon more than small residences, but individual classrooms in poorly ventilated areas can accumulate significant concentrations.
    • Variable ventilation: Older school buildings frequently have inadequate or inconsistent mechanical ventilation, allowing radon to accumulate during the school day.

    EPA’s School Radon Testing Program

    EPA does not federally mandate radon testing in schools — there is no federal law requiring schools to test. However, EPA has published detailed guidance through its “Radon in Schools” program, recommending testing of all ground-level and below-grade spaces in school buildings. EPA provides free technical assistance to states and school districts through this program.

    EPA’s recommended action level for schools is the same as for residences: 4.0 pCi/L. EPA recommends that schools test every 5 years and after any major renovation that affects the foundation, HVAC, or building envelope.

    State Requirements for School Radon Testing

    Several states have enacted mandatory radon testing requirements for schools:

    • Illinois: Requires radon testing in all public schools; has established a state school radon testing program
    • New Jersey: Requires periodic radon testing in public schools
    • Pennsylvania: Has enacted school radon testing requirements
    • Iowa: State radon program provides resources for school testing; requirements have evolved
    • Other states: Requirements vary and change — check your state’s radon program or department of education for current mandates

    In states without mandatory testing, individual school districts may have adopted their own radon testing policies. Many districts in high-radon zones (EPA Zone 1) test voluntarily regardless of state mandate.

    AARST-ANSI SGM-SF Standard for Schools

    AARST-ANSI SGM-SF (Standard for Radon Mitigation in Schools, Large Buildings, and Multifamily Structures) governs both testing and mitigation in school buildings. Key differences from residential standards:

    • School buildings must be tested by a certified measurement professional (not DIY testing)
    • Short-term tests (48–96 hours) must be conducted during school occupancy and under normal HVAC operating conditions — not during summer break or weekends when HVAC schedules may differ
    • Testing must cover each “test area” (room or zone with a separate HVAC zone or floor level)
    • Results above 4.0 pCi/L trigger mitigation planning requirements
    • Post-mitigation testing must be conducted by an independent certified professional, not the installing contractor

    What Parents Can Do

    • Ask whether your school has been tested: Request the most recent radon test results from the school principal or district facilities manager. In states with public disclosure requirements, results may be available through the state radon program or department of education.
    • Ask when the school was last tested: EPA recommends testing every 5 years. If your school has not tested within that window, request that testing be scheduled.
    • Advocate for testing through the school board: If the district has not tested and is not responsive to individual requests, bringing the matter to the school board is the next step. Present EPA’s school radon guidance documents as the basis for the request.
    • Contact your state radon program: State programs often provide testing resources, technical assistance, or can apply pressure on districts that are not complying with state requirements.

    Radon in Daycares and Childcare Facilities

    Daycares and childcare facilities face the same radon risks as schools, with an additional concern: infants and toddlers spend much of their day on the floor — closer to radon entry surfaces — and breathe at higher respiratory rates than adults, increasing intake of radon decay products per unit of time.

    State licensing requirements for childcare facilities may include radon testing as a condition of operation in high-radon states. Even where not required, reputable childcare facilities in radon-prone areas should test and disclose results to parents.

    Frequently Asked Questions

    Are schools required to test for radon?

    There is no federal mandate for radon testing in schools. Several states (including Illinois, New Jersey, and Pennsylvania) have enacted mandatory school testing requirements. In other states, testing is voluntary — though EPA strongly recommends it for all ground-level and below-grade school spaces. Check your state’s radon program or department of education for current requirements.

    Can parents request radon test results from their child’s school?

    Yes. In most states, school radon test results are public records and must be disclosed upon request. Start by requesting results from the school principal or district facilities manager. If results are unavailable or the school has not tested, escalate to the school board and contact your state radon program for assistance.

    What happens if a classroom tests above 4.0 pCi/L?

    Under EPA guidance and AARST SGM-SF, a result above 4.0 pCi/L in a school space requires mitigation planning and action. The affected space should not be used for extended occupancy until mitigation is complete and post-mitigation testing confirms levels below 4.0 pCi/L. Schools may close affected classrooms, relocate occupants to above-grade spaces, or implement interim ventilation measures while permanent mitigation is installed.

  • NRPP and NRSB Radon Certification: What They Are and Why They Matter

    The Distillery — Brew № 1 · Radon Mitigation

    Two national organizations certify radon professionals in the United States: the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB). Both are EPA-recognized, both administer examinations and continuing education requirements, and both maintain searchable directories of currently certified professionals. Knowing which certification to look for — and how to verify it — protects you from uncertified contractors and ensures your test results or installation will be accepted by real estate transactions, state programs, and regulatory authorities.

    NRPP: National Radon Proficiency Program

    NRPP is administered by the American Association of Radon Scientists and Technologists (AARST). It is the larger of the two national certification programs, with thousands of currently certified professionals across measurement and mitigation disciplines.

    NRPP Certification Categories

    • Radon Measurement Professional (RMP): Certified to conduct radon measurements in residential and commercial buildings using EPA-approved and AARST-standard protocols. Required for conducting certified real estate measurements in most states.
    • Radon Mitigation Specialist (RMS): Certified to design and install radon mitigation systems per AARST-ANSI standards (SGM-SF for slab/basement, RMS-LB for large buildings). Required for mitigation work in states with licensing requirements.
    • Radon Service Provider (RSP): Business-level certification allowing a company to offer radon services under a certified individual’s license.

    NRPP Certification Requirements

    • Approved training course completion
    • Written examination with passing score
    • Continuing education (16 hours per 2-year certification cycle)
    • Current certification renewal every 2 years

    Verify NRPP Certification

    Search the NRPP directory at nrpp.info. Enter the professional’s name or certification number to confirm current status and discipline (measurement vs. mitigation). Certification can lapse — always verify before engaging a professional, not after the work is complete.

    NRSB: National Radon Safety Board

    NRSB is an independent certification body unaffiliated with AARST. It is the smaller of the two national programs but is equally recognized by EPA and most state radon programs. Some states specify acceptance of NRSB, NRPP, or both.

    NRSB Certification Categories

    • Radon Measurement Technician (RMT): Entry-level measurement certification
    • Certified Radon Measurement Professional (CRMP): Advanced measurement certification with additional requirements
    • Radon Mitigation Technician (RMiT): Entry-level mitigation certification
    • Certified Radon Mitigation Professional (CRMiP): Advanced mitigation certification

    Verify NRSB Certification

    Search the NRSB directory at nrsb.org. Enter name or certification number to confirm current status.

    State Certification Programs

    Many states have their own radon certification or licensing requirements that operate alongside or instead of NRPP/NRSB. States with independent radon certification programs include Illinois, Iowa, Minnesota, New Jersey, New York, Pennsylvania, and others. In these states:

    • A state license may be required in addition to NRPP/NRSB certification
    • A state license alone (without NRPP/NRSB) may be sufficient for in-state work
    • Real estate transaction tests may specifically require state-licensed professionals

    Check your state health department’s radon program website for current state-specific licensing requirements. Requirements change — information from multiple years ago may be outdated.

    Measurement vs. Mitigation Certification: Important Distinction

    Radon certification is discipline-specific. A Radon Measurement Professional (NRPP) is certified to test — not to install systems. A Radon Mitigation Specialist (NRPP) is certified to install — not necessarily to conduct certified measurements. Some professionals hold both certifications; many hold only one.

    This distinction matters because: allowing the installing contractor to conduct the post-mitigation test removes the independent verification that gives the result credibility. Best practice is independent post-mitigation testing by a certified measurement professional separate from the installing contractor — particularly for real estate transactions and warranty documentation.

    When Certification Is Required

    • Real estate transactions: Most states that mandate testing specify certified professional testing. Even in states without mandates, buyers and their agents routinely require it.
    • State-regulated rental property testing: States with landlord testing requirements typically specify certified professional measurement.
    • Federally assisted housing: HUD radon protocols require certified professionals for testing and mitigation in applicable properties.
    • Schools and public buildings: EPA’s school radon guidance and AARST-ANSI SGM-SF standard specify certified measurement professionals for school testing programs.
    • Mitigation under state licensing laws: In states with radon contractor licensing requirements, performing mitigation work without a license is illegal regardless of NRPP/NRSB status.

    Frequently Asked Questions

    What is the difference between NRPP and NRSB certification?

    Both are EPA-recognized national radon certification programs. NRPP is administered by AARST and is the larger program; NRSB is an independent organization. Both require examination, approved training, and continuing education. For practical purposes, a currently certified professional from either program meets the requirements for most real estate and state program contexts — though individual state programs may specify a preference. When in doubt, verify that your state’s radon program accepts the specific certification held by the professional you are engaging.

    Can a radon mitigator also test for radon?

    Only if they hold both a Radon Mitigation Specialist certification and a Radon Measurement Professional certification. Mitigation-only certification does not authorize certified measurement work. In states that specifically prohibit the installing contractor from conducting the post-mitigation test, even dual-certified professionals may not be permitted to self-certify their own installation results.

    How do I verify a radon contractor’s certification?

    Request the contractor’s NRPP or NRSB certification number and verify it directly at nrpp.info (NRPP) or nrsb.org (NRSB). Both sites have searchable real-time directories. A contractor who cannot or will not provide a verifiable certification number should not be engaged for certified measurement or mitigation work.

  • How Radon Levels Change: Seasonal and Daily Fluctuations Explained

    The Distillery — Brew № 1 · Radon Mitigation

    If you have ever wondered why two radon tests in the same home, months apart, produced different results — or why your continuous monitor shows radon spiking on some days and dropping on others — the answer is that radon levels are not static. They fluctuate continuously in response to atmospheric pressure, temperature differentials, wind, precipitation, and your home’s mechanical systems. Understanding this variability helps you interpret test results correctly and avoid both over-reaction and under-reaction to single data points.

    Why Radon Levels Fluctuate

    Radon is produced continuously in the soil from the radioactive decay of uranium and radium — the production rate is essentially constant. But how much of that radon enters your home depends on the pressure differential between the sub-slab zone and your home’s interior. When sub-slab pressure is lower than interior pressure, radon is suppressed. When the sub-slab is at higher pressure than the interior — the typical situation — radon is driven inward through any available pathway.

    This pressure differential changes constantly.

    Barometric Pressure: The Dominant Driver

    Falling barometric pressure is the single strongest predictor of elevated radon on any given day. When atmospheric pressure drops (as a low-pressure weather system approaches), the pressure differential between the soil and the home increases — the soil acts like a sponge being squeezed, releasing radon upward into any available pathway.

    Research published in the journal Health Physics and other radon science literature consistently shows radon spikes of 30–100% above baseline during periods of falling barometric pressure, with values returning toward baseline as pressure stabilizes or rises. A 48-hour radon test conducted during the passage of a major weather system may capture readings 50% above or below the home’s true average.

    Temperature Differential: The Stack Effect

    The stack effect describes the tendency of warm air to rise through a building. Warm interior air creates upward pressure that draws air in from the bottom — including soil gas through any sub-slab pathways. The stack effect is strongest when the temperature differential between interior and exterior is greatest.

    • Winter: Large indoor-outdoor temperature differential = strong stack effect = more radon drawn in from soil. Winter typically produces the highest radon readings of the year in most U.S. climates.
    • Summer: Small or reversed indoor-outdoor temperature differential (especially in air-conditioned homes where interior is cooler than exterior) = weakened stack effect = less radon drawn in. Summer typically produces the lowest readings.
    • Day vs. night: Overnight temperatures drop; if the home cools slightly relative to the soil temperature, the evening and early morning hours can show elevated radon compared to midday.

    Wind

    Wind creates complex pressure patterns around buildings. Windward walls experience positive pressure (wind pushing against the building) while leeward walls experience negative pressure (suction on the downwind side). These pressure differences can create asymmetric sub-slab pressure patterns — drawing more radon into portions of the foundation on the leeward side.

    Strong wind can also occasionally reverse airflow in a passive radon vent pipe, temporarily reducing passive system effectiveness. Active systems with fans are unaffected by wind.

    Precipitation

    Heavy rainfall temporarily reduces radon entry by saturating the soil around the foundation. Water-saturated soil has lower gas permeability — radon cannot move through water-filled pore spaces as easily as through air-filled ones. During and immediately after heavy rain, radon readings often drop 20–40%. This effect reverses as the soil dries over the following days.

    Paradoxically, prolonged drought can also affect radon — extremely dry, cracked soil develops preferential pathways through cracks in the clay that allow more rapid radon movement. The relationship between soil moisture and radon is not linear.

    HVAC Operation

    Your home’s mechanical systems affect indoor radon in two ways: dilution and pressure. Forced-air systems recirculate interior air, diluting radon concentration as the air volume cycles through the system. But the same system, when it creates negative pressure in the basement (as return air is drawn in), can increase radon entry from the soil. The net effect varies by system configuration and home construction.

    What This Means for Testing

    Short-term tests (48–96 hours) capture radon levels during a specific window affected by all of these variables simultaneously. This is why:

    • EPA recommends a confirmatory test when initial short-term results fall in the 4.0–8.0 pCi/L range — one test may capture an anomalously high or low period
    • Long-term tests (90 days to 1 year) are more representative of actual annual average exposure — they average across multiple high and low cycles
    • Winter tests are more conservative (higher-risk representation) than summer tests for the same home
    • A single continuous monitor reading should not trigger a mitigation decision — wait for a 30-day average at minimum before comparing to the 4.0 pCi/L action level

    Frequently Asked Questions

    Why did my radon test show different results on different days?

    Radon levels fluctuate 30–50% day to day in many homes, driven by barometric pressure changes, temperature differentials, wind, and precipitation. This variability is normal and expected. A continuous monitor will show these day-to-day fluctuations clearly — the 30-day and long-term averages are more meaningful than any single day reading.

    Is radon higher in winter or summer?

    Winter typically produces higher radon readings in most U.S. homes — closed windows, stronger stack effect from the large indoor-outdoor temperature differential, and lower barometric pressure during winter weather systems all contribute. Summer readings with open windows may be substantially lower. This is why EPA requires closed-house conditions for short-term tests: to control for the ventilation effect that artificially lowers summer readings.

    My radon monitor showed a spike to 12 pCi/L for one day — should I be concerned?

    A single-day spike is worth noting but not cause for immediate alarm. Look at the context: was it during a significant weather event (falling barometric pressure, storm passage)? Has the 7-day or 30-day average also been elevated? If the short-term spike is an outlier in an otherwise normal-range long-term average, it likely reflects a pressure event. If the 30-day average is also approaching or above 4.0 pCi/L, that warrants a formal short-term or long-term test for confirmation.

  • Radon Testing in Apartments and Condos: What Tenants Need to Know

    The Distillery — Brew № 1 · Radon Mitigation

    Radon is commonly associated with single-family homes, but apartment and condominium residents face meaningful radon exposure risk — particularly in garden-level and first-floor units. The key differences from homeowner situations: tenants typically cannot install mitigation systems themselves, disclosure requirements vary significantly by state, and the responsibility for testing and remediation rests with the property owner or landlord.

    Which Apartment Units Are at Risk

    Radon enters buildings from the soil through the foundation — the same mechanism as in single-family homes. In multistory apartment buildings and condominiums:

    • Garden-level and below-grade units: Highest risk. Units partially or fully below grade are in direct contact with the soil and foundation, similar to a basement in a single-family home.
    • First-floor units: Elevated risk compared to upper floors. Radon entering the building from the foundation may concentrate on the lowest floors before dispersing upward.
    • Upper-floor units (2nd floor and above): Lower risk. Radon entering the basement or first floor is diluted by building air exchange before reaching upper levels. However, radon can still accumulate in poorly ventilated upper-floor units in some building types.
    • Slab-on-grade construction (no basement): First floor units in slab construction may have direct soil-contact risk similar to a single-family slab home.

    Testing in Rental Units

    Tenants can conduct their own radon tests in their rental unit using standard DIY charcoal canisters — the same devices used in single-family homes. Placement protocol is identical: lowest floor of your unit (for most tenants this is the main living level), breathing zone, away from HVAC vents and windows.

    Before testing, check your lease: some leases restrict modifications or installations without landlord consent. A charcoal canister placed on a shelf does not constitute a modification — but a continuous electronic monitor plugged into an outlet may warrant a conversation with the landlord first in some jurisdictions.

    Landlord Obligations: State-by-State

    Federal law does not mandate radon testing or disclosure in rental properties. State requirements vary substantially:

    • States with landlord radon testing or disclosure requirements: Illinois requires radon disclosure in certain circumstances; Maine has radon disclosure requirements for property transfers; other states have specific requirements for subsidized housing or federally assisted properties. Requirements change — check your state health department’s current radon program guidance.
    • HUD and federally assisted housing: The Department of Housing and Urban Development (HUD) has established radon testing and mitigation requirements for federally assisted multifamily housing in high-radon zones. Tenants in HUD-assisted housing in EPA Radon Zone 1 states have specific protections.
    • Implied habitability: In states without specific radon laws, elevated radon may qualify as a habitability issue under general landlord-tenant law — particularly if the landlord has been notified of elevated levels and refuses to address them. This is a developing area of law that varies by jurisdiction.

    What to Do If Your Test Shows Elevated Radon

    • Document the result: Keep the lab report, note the test dates, device placement location, and conditions during the test
    • Notify your landlord in writing: Send written notice (email with read receipt, or certified mail) providing the test result and requesting remediation. Keep a copy of all correspondence.
    • Reference your state’s requirements: Include any applicable state radon disclosure or habitability statute in your request
    • Contact your state radon program: Most states have a radon program (through the health or environment department) that provides guidance to tenants and can sometimes mediate landlord disputes
    • Consult a tenant’s rights organization or attorney: In states where elevated radon may implicate habitability, a brief legal consultation clarifies your options

    Mitigation Options for Renters

    Tenants generally cannot install permanent radon mitigation systems without landlord consent — installing a core hole through the concrete slab and running pipe through walls requires property owner authorization and typically a building permit. However, some options exist:

    • Request landlord-installed mitigation: The most appropriate path — and the landlord’s obligation in states with relevant statutes or under implied habitability doctrine
    • HEPA air purifiers with activated carbon: Some reduction in radon decay product attachment to airborne particles, reducing the fraction that deposits in lung tissue. Not a substitute for source control but can provide modest supplemental reduction in a unit where mitigation is delayed.
    • Increased ventilation: Opening windows when weather permits reduces radon concentration through dilution. Not a permanent solution but may reduce short-term exposure while advocacy with the landlord proceeds.
    • Relocation: In severe cases with unresponsive landlords and no legal remedy, relocating to a non-ground-floor unit or a different property may be the practical solution

    Frequently Asked Questions

    Is radon a problem in high-rise apartments?

    Above the second floor, radon risk diminishes substantially in most building types. High-rise apartments on upper floors rarely have elevated radon because soil gas entering the building at the foundation is diluted by the building’s air volume before reaching upper floors. Ground-floor and below-grade units are the primary concern in multifamily buildings.

    Can I make my landlord fix a radon problem?

    It depends on your state. In states with specific radon statutes, landlords have defined obligations. In other states, the implied warranty of habitability may apply — elevated radon that poses a health risk could constitute a habitability defect, particularly if the landlord has been notified and refuses to act. A tenant’s rights attorney in your state can advise on specific remedies available.

    My apartment is on the third floor — should I still test for radon?

    Third-floor radon is uncommon but not impossible, particularly in older multifamily buildings with poor air exchange, poorly ventilated common areas, or building materials (concrete, granite) that emit radon directly. Testing is inexpensive and provides certainty. If your third-floor result is elevated, it is unusual enough to warrant a second test before assuming it is accurate — and a conversation with building management about whether lower floors have been tested.

  • Where to Place a Radon Test in Your Home

    The Distillery — Brew № 1 · Radon Mitigation

    Radon test placement is not optional or approximate — it is the single most controllable variable in the measurement process. A correctly purchased device from a certified lab, placed in the wrong location, produces a misleading result. EPA’s placement protocol exists to ensure the result reflects actual exposure in the breathing zone of living areas, not the conditions in a corner of a mechanical room or under an HVAC vent.

    Which Floor to Test

    Always test in the lowest level of the home that is used or could be used as living space. This includes:

    • Finished basements: Test here, even if the basement is used only occasionally
    • Unfinished basements: Test here if the basement could be converted to living space in the future, or if family members spend any time there (laundry, exercise, storage retrieval)
    • First floor (no basement): If there is no basement or crawl space, the first floor is the lowest testable level
    • Slab-on-grade main level: Test on the main living floor if the home has no basement

    Do not test only on the second or third floor if a basement exists. Radon accumulates most at the lowest points of the home — testing only upper floors systematically underestimates actual exposure in the most radon-concentrated zones.

    Height: Breathing Zone Placement

    Place the test device in the breathing zone:

    • Minimum height: 20 inches (approximately 50 cm) above the floor
    • Maximum height: No strict upper limit, but ceiling height (where air stratification may occur) is not appropriate
    • Ideal range: Tabletop height (28–36 inches) to mid-wall (48–60 inches) — where occupants breathe while sitting or standing in the room

    Placing a device directly on the floor is wrong — floor-level air is not breathing-zone air, and radon concentrations near the floor (especially on a concrete slab) may be artificially elevated due to proximity to the entry surface. Placing a device on a high shelf near the ceiling introduces stratification effects and may not represent the breathing zone.

    Distance from Walls and Other Surfaces

    • Minimum wall distance: 12 inches (30 cm) from any wall or vertical surface
    • Window and door distance: Away from any window, door, or other exterior opening that creates air movement
    • HVAC vent distance: At least 36 inches from any supply or return vent — HVAC airflow creates local turbulence that can either dilute or concentrate radon at the measurement point artificially
    • Sump pit distance: Not near the sump pit — sump pits are radon point sources; proximity will produce artificially high readings that do not represent room-average concentration

    Rooms to Avoid

    EPA’s placement protocol explicitly excludes certain room types:

    • Kitchens: Cooking exhaust fans create pressure differentials; moisture and humidity affect charcoal adsorption
    • Bathrooms: Exhaust fans and high humidity; not representative of general living space
    • Laundry rooms: Dryer exhaust creates pressure changes; humidity from washing
    • Closets: Restricted airflow — not representative of breathing-zone air in the room
    • Crawl spaces: Not a living area; radon in the crawl space does not directly represent living-space concentration
    • Unheated garages: Not conditioned living space; pressure dynamics differ from the home interior

    Ideal Room Characteristics

    The ideal test location is:

    • A room regularly used by occupants — bedroom, living room, family room, home office
    • On the lowest floor with living activity
    • Central to the room — not tucked against the radon-entry-pathway slab edge or a foundation wall
    • Away from windows and exterior doors
    • Not directly above or adjacent to the sump pit
    • Accessible but undisturbed — the device should not be moved during the test period

    Multiple Test Locations

    EPA recommends testing each room used as sleeping quarters if those rooms are on different floors. For a typical single-family home, one test device on the lowest living level is the standard initial screen. For a more complete picture — particularly if you have a finished basement with a bedroom and a first-floor primary bedroom — placing devices in both locations simultaneously provides more information about exposure during sleep hours.

    Multiple simultaneous tests do not need to be averaged — each result reflects the conditions in that specific room. Address any room reading above the EPA action level of 4.0 pCi/L.

    Testing After Mitigation: Same Protocol

    Post-mitigation test placement follows the same rules — lowest livable level, breathing zone, away from drafts and sump pits. Place the post-mitigation test device in the same room (or as close as possible to the same location) as the pre-mitigation test to enable a direct before/after comparison. This is not strictly required but simplifies interpretation.

    Frequently Asked Questions

    Should I test for radon in the basement or on the first floor?

    Test in the basement if you have one — it is the lowest living level and where radon concentrations are highest. If the basement is unfinished and never occupied, you can also test on the first floor, but EPA recommends testing where people actually spend time. If you plan to finish the basement, test there first — before any renovation work that might seal in or redistribute radon entry pathways.

    Can I put a radon test on my nightstand?

    Yes — a nightstand is an excellent location if it is in the bedroom on the lowest sleeping floor. It is at breathing-zone height, in a room where you spend 7–8 hours nightly, and typically away from drafts and HVAC vents. Just confirm the nightstand is at least 12 inches from the wall and not adjacent to a window or exterior door.

    My basement has multiple rooms — where should I put the test?

    Choose a room you use or plan to use. If one room is a home office or bedroom and others are storage, test in the occupied room — that is where your actual exposure occurs. If all basement rooms are unfinished storage, test in the most central location accessible to you, then retest in the finished space after renovation if you later convert it to living use.