Radon above 200 Bq/m³ — investigate, remediate, re-measure

If the long-term measurement shows an annual average above 200 Bq/m³, the level must be reduced. The reference level is not a limit value that triggers a sanction in itself, but exceeding it in a dwelling can constitute a detriment to human health (olägenhet för människors hälsa) under the Swedish Environmental Code — and then the owner's duty under Chapter 9, Section 9 to take the measures that can reasonably be required applies. The municipal environmental committee can order you to investigate and to remediate.

The order below is not arbitrary. It is sorted by what tends to solve the problem most cheaply, and step one is almost always skipped.

1. Find the source before you remediate

Radon comes from three directions and they call for entirely different remedies:

Source	Signature	Remediation path
Soil radon	Highest on the ground floor and in spaces with ground contact, varies with wind and pressure	Sealing against the ground, radon suction, radon well
Building material (blue concrete)	More even levels throughout the building, including upper floors	Ventilation; in severe cases surface treatment or replacement
Radon in water	Only relevant with a private drilled well	Separation in the water

Distinguishing soil radon from building material is done in practice with a gamma radiation measurement in the building combined with how the levels distribute across floors. Without that investigation you are remediating blind, and the usual consequence is sealing against the ground in a house whose problem is in the walls.

2. Look at the ventilation first

If ventilation is undersized or not functioning, this is often both the cheapest and the fastest remedy, and it resolves some cases outright. Radon and ventilation control overlap directly here: a ventilation inspection with remarks about low extract flows in a building with elevated radon is the same case seen from two directions. See ventilation remarks.

Watch for the reverse as well. Added insulation or a window replacement carried out without adjusting the ventilation may have created the problem in a building that previously met the reference level.

3. Engineer out the source

For soil radon: sealing penetrations and cracks against the ground, a radon sump creating negative pressure beneath the slab, or a radon well. For building material: increased air exchange, and in harder cases work on the surfaces.

We quote no figures — the cost varies too much with building, source and access for a number to be anything but misleading. The Swedish Radiation Safety Authority (Strålsäkerhetsmyndigheten) and Boverket are the sources for choice of method.

4. Re-measure — and allow for the calendar

After remediation a new long-term measurement is required. Not a short-term measurement, not an indicative one: a full measurement over at least 60 days within the measuring season of 1 October to 30 April, with the same detector placement as the original so the values are comparable.

That carries an unwelcome but unavoidable planning consequence. If a building is remediated in May, the effect can be confirmed at the earliest after the turn of the year. There is no way to shorten it, which is why the investigation step is worth the time — a wrong remedy costs not only the money but a whole year.

How quickly must we remediate?

There is no statutory deadline. The deadline is set in practice by the environmental committee in its order, and depends on how high the level is, what kind of space it is, and how extensive the remedy is. The committee may allow anything from a few months to a couple of years for a structural measure.

What you control is the starting position. A portfolio that volunteers a remediation plan with prioritised buildings and dates generally receives a deadline built on that plan. A portfolio that does not respond receives one built on the committee's own judgement.

What residents can do — and what that means for you

A tenant or co-operative member who suspects elevated radon can approach the municipal environmental committee, which may then open a supervision case against you as owner. In a rental property the owner is responsible for measurement and remediation, and in a co-operative the association — never the resident.

Practical consequence: keep residents informed of what the measurement showed and what you intend to do. A supervision case that starts with a complaint takes more time than one you drive yourself.

Read on: radon measurement — requirements, reference level and responsibility for how measurement is done, and radon in workplaces if the portfolio contains commercial premises.