2.2 Test Location Selection & Multi-Foundation Planning

Test Location Selection & Multi-Foundation Planning

Accurate radon measurement depends fundamentally upon selecting the correct test location within a building. A measurement conducted in an improper room or on an incorrect floor level yields invalid data that can misrepresent occupant exposure, lead to flawed real estate decisions, or fail to satisfy national compliance standards. This section details the protocol guidelines established by ANSI/AARST MAH-2023 (Protocol for Conducting Measurements of Radon and Radon Decay Products in Homes) for selecting test locations, managing complex multi-foundation structures, and executing testing across multi-family and commercial properties.

Fundamental Principles of Test Location Selection

The primary objective of a radon measurement evaluation is to assess occupant exposure potential under standardized, reproducible conditions. To achieve this, ANSI/AARST MAH-2023 mandates that initial radon testing in single-family residential properties be performed in the lowest level suitable for occupancy.

Defining the "Lowest Level Suitable for Occupancy"

Determining the lowest level suitable for occupancy requires professional judgment applied against clear standardization rules:

• Occupied Lived-in Space: Any finished room currently used for living, sleeping, working, or recreation—such as a basement bedroom, finished family room, den, or home office—is classified as occupied space and must be prioritized for detector placement.
• Unfinished Space Capable of Conversion: An unfinished basement or lower-level space that is not currently finished with drywall or carpet IS STILL considered suitable for occupancy if it could be adapted for living use without major structural modifications. Key criteria include:
  • Adequate head room (typically 6.5 to 7 feet or higher ceiling clearance).
  • Absence of chronic flooding, standing water, or severe structural dampness.
  • Safe, permanent stair access from upper living levels.
  • Structural potential to be finished into a bedroom, workshop, gym, or family area.
• Rationale for Real Estate Testing: In real estate transactions, testing the lowest level suitable for occupancy is mandatory because future buyers or occupants may finish the basement or alter space utilization. Testing this level provides a conservative, protective assessment of maximum potential exposure within the home.
• Unsuitable Spaces: Shallow, damp cellars, root cellars with low ceiling height (<6 feet), crawlspaces with exposed earth, and unconditioned attics are not suitable for occupancy and must never serve as test device placement sites.

Multi-Foundation Planning & Combination Structures

Modern residential construction frequently incorporates multiple foundation designs within a single building footprint. For example, a house may feature a 1970s poured concrete basement, a 1990s slab-on-grade family room addition, and a 2010 master bedroom suite built over an unvented crawlspace.

Mandatory Multi-Foundation Rule

Under ANSI/AARST MAH-2023, when a building contains combination or multi-foundation structures, the measurement professional must place at least one test device in the lowest suitable living area above each distinct foundation footprint in contact with the soil.

In a combination basement, slab-on-grade, and crawlspace home:

1. Basement Segment: One detector is placed in the lowest lived-in room (or unfinished conversion-capable area) of the basement footprint.
2. Slab-on-Grade Addition: A second detector is placed in the ground-contact room situated directly over the slab-on-grade addition.
3. Crawlspace Segment: A third detector is placed in the ground-contact room situated directly over or adjacent to the crawlspace footprint.

Each foundation footprint contacts a unique geological micro-environment with distinct sub-slab gravel, moisture, and pressure dynamics. Testing only the basement in a multi-foundation home can severely underestimate radon levels in a slab addition that sits over a separate high-radon soil hotspot.

Specific Room Selection Criteria: Approved vs. Prohibited Spaces

Once the correct floor level and foundation footprint are identified, the measurement professional must select the specific room for device deployment.

Approved Test Rooms

Detectors should be placed in rooms that are regularly occupied for extended periods:

• Bedrooms: Highly recommended, as occupants spend 6 to 8 continuous hours sleeping in these locations.
• Family Rooms and Living Rooms: Primary gathering spaces where occupants spend substantial leisure time.
• Dens and Home Offices: Frequently occupied workspaces.

Prohibited Test Locations

Detectors must NEVER be placed in the following restricted areas:

• Kitchens: High localized thermal currents, range hood exhaust fans, and steam from cooking distort air movement and radon decay product equilibrium.
• Bathrooms: High relative humidity, steam, condensation on detector media, and bath exhaust fan depressurization invalidate results.
• Laundry Rooms: Clothes dryer exhaust vents create severe depressurization, while high humidity from washing appliances degrades passive charcoal detectors.
• Closets, Hallways, and Pantries: Restricted air circulation in small, closed spaces creates micro-climates that do not represent general room air.
• Utility / Mechanical Rooms: Proximity to furnaces, water heaters, and ductwork exposes detectors to high air velocity and localized thermal currents.
• Near Exterior Doors or Windows: Drafts from window/door operation disrupt static air conditions.

Multi-Family and Large Commercial Building Protocols

Testing protocols for multi-family residential buildings (apartments, condominiums) and commercial properties (schools, office buildings) differ significantly from single-family rules:

• 100% Ground-Contact Dwelling Units: In multi-family properties, ANSI/AARST MAMF-2023 mandates testing every single ground-contact dwelling unit (any apartment or condo in direct soil contact or situated directly over an unconditioned basement or crawlspace).
• Upper Floor Sampling: In addition to 100% ground-contact testing, upper floors require statistical sampling (typically 10% of upper-floor units) to check for potential radon migration through elevator shafts, utility chases, or building materials.
• Commercial / Open Area 2,000 Sq Ft Rule: For large commercial spaces, schools, open office bays, auditoriums, and warehouses, ANSI/AARST MALB-2023 specifies placing one detector for every 2,000 square feet (190 m²) of open floor space in contact with the soil, in addition to testing every individual enclosed office or classroom.

Residential Layout Test Location Decision Matrix