Measurement is what turns potential into evidence
Radon is a naturally occurring radioactive gas that can enter buildings from the ground. Geological maps and local experience can indicate potential, but they cannot establish the concentration in an individual room. Construction, cracks, service penetrations, pressure differences, ventilation and occupant behaviour all influence the result.
The Danish Health Authority therefore emphasises measurement. For long-term assessment it recommends measurements over at least two months during the heating season, following SBi Guideline 270. That duration reduces the risk of treating a short-lived operating condition as representative of the building's annual performance.
Start with occupied spaces
A measurement plan should identify where people spend significant time. In a home that may include bedrooms and living rooms. In a commercial property it can include offices, meeting rooms, reception areas, classrooms, canteens, locker rooms and regularly used basement workspaces.
Ground-contact and lower-level rooms usually deserve particular attention, but the plan should also consider vertical connections, stairwells, service risers and ventilation zones. A detector in an unused basement store may be useful diagnostically, yet it cannot replace measurement in the occupied room whose exposure is being assessed.
Placement details protect the quality of the result
These controls are simple, but on a multi-property programme they determine whether results can be compared and whether a surprising value can be investigated with confidence.
- Place detectors in representative rooms and record the exact location.
- Avoid positions immediately beside windows, doors, vents, heat sources or direct sunlight unless the measurement design specifically requires it.
- Keep the building in normal use and record material changes to occupancy, ventilation or heating.
- Use enough detectors to represent different floor levels, uses and building zones.
- Maintain a clear chain between detector ID, property, room and laboratory result.
Interpret the pattern, not only the highest number
The Social and Housing Agency recommends reducing radon in existing buildings when the level exceeds 100 Bq/m³. It recommends simple and inexpensive improvements between 100 and 200 Bq/m³ and more effective improvements above 200 Bq/m³. New buildings must be radon-protected so the level remains below 100 Bq/m³.
A portfolio response should still consider the full pattern. Are elevated results concentrated in one wing, one floor or one ventilation zone? Do occupied rooms differ from adjacent technical spaces? Could a detector have been disturbed? The answers help distinguish a local defect from a building-wide issue and guide the next diagnostic step.
Match the remedy to the entry route
Possible measures include sealing penetrations and cracks, adjusting ventilation, improving pressure balance or installing a radon sump or sub-slab extraction system. The appropriate response depends on the concentration, building construction, use and likely entry route.
Any intervention should be followed by measurement. Improved ventilation may reduce radon but also affect energy use, comfort and moisture behaviour. A good solution therefore treats radon as a building-performance question, not as an isolated laboratory number.
Official sources