Radon for Trades UK 2026 — Risk, Testing & Building Regs Protective Measures

What Radon Actually Is

Radon is a naturally occurring radioactive gas. It's produced by the radioactive decay of uranium, which is present in small amounts in nearly all rocks and soils. As the gas forms underground it seeps upward through cracks and gaps and, outdoors, disperses harmlessly. The problem comes when it enters a building — through floor slabs, service entries, gaps around pipes and cracks in foundations — and builds up indoors where there's nowhere for it to disperse.

It's colourless, odourless and tasteless, so there is no way to detect it without measurement. Levels are highest in basements, cellars and ground-floor rooms because that's where the gas enters and concentrates. The amount of radon in any given building depends heavily on the local geology, which is why it's very much a regional issue.

Higher-risk areas in the UK include parts of the South West (Cornwall and Devon are the best-known), the Pennines, parts of Wales, Northamptonshire, Derbyshire and various parts of Scotland. But radon is found at varying levels across the whole country, and a postcode-level check is the only reliable way to know what you're dealing with on a specific site.

Why It Matters — The Health Risk

Radon is the second-biggest cause of lung cancer in the UK after smoking, and the largest single source of natural radiation exposure for most people. When you breathe in radon, the radioactive decay products can lodge in the lung and the radiation damages lung tissue over time. The risk is dose-related — the higher the concentration and the longer the exposure, the greater the risk.

The UK Health Security Agency (UKHSA) measures radon concentration in becquerels per cubic metre (Bq/m³). It publishes radon-affected-area maps and two key benchmarks for homes: an Action Level of 200 Bq/m³, above which UKHSA strongly recommends remediation, and a lower Target Level of 100 Bq/m³, which is the level people are encouraged to aim for. The risk doesn't suddenly switch on at the Action Level — lower levels still carry some risk — but these figures set the points at which action is advised.

Employer Duties: Radon in the Workplace

If you employ people — or work in premises yourself — radon is a workplace health and safety matter. Under the Health and Safety at Work etc. Act 1974 and the Management of Health and Safety at Work Regulations 1999, you have a general duty to assess risks to health. Where radon could be present at significant levels, that duty extends to assessing radon exposure.

The specific radiation legislation is the Ionising Radiations Regulations 2017 (IRR17). These set a workplace reference level of 300 Bq/m³ averaged over the year. If radon in a workplace exceeds that level, the employer comes within the scope of IRR17 and must take action to reduce exposure, and may have further duties around monitoring and record-keeping.

In practice, the duty bites hardest on below-ground workplaces (basements, cellars, service tunnels) and ground-floor workplaces in radon-affected areas, because those are where levels are most likely to be elevated. The HSE expects employers in affected areas to find out whether they have a problem rather than assume they don't.

How Workplace Testing Works

Radon fluctuates day to day and season to season, so a single spot reading is meaningless. The standard method is to place small passive detectors in the relevant rooms and leave them in place for around three months — typically over the winter heating season when levels tend to be highest. The detectors are then sent to a laboratory which calculates the average annual concentration. UKHSA and a number of accredited providers offer validated workplace measurement schemes.

If the result is below the reference level, you keep the record and you're done. If it's above, you remediate — usually by improving sub-floor ventilation, sealing entry routes or installing active depressurisation — and then re-measure to confirm the fix worked.

Building Regulations: Protective Measures in New Work

This is the part that catches builders out most often. In England and Wales, Approved Document C (site preparation and resistance to contaminants and moisture) requires that buildings be protected against radon where the site is in a radon-affected area. The technical detail sits in the BRE guidance document BR 211, "Radon: guidance on protective measures for new buildings", which building control and designers work from.

The requirement applies not just to new dwellings but to extensions, conversions and certain change-of-use work in affected areas. The level of protection required depends on the radon probability band for the specific site — and that's determined by postcode and a site-specific assessment, not a guess. BR 211 sets out two tiers:

• Basic protection — a continuous radon-proof membrane (barrier) across the whole footprint of the building, with all joints sealed and carefully detailed around service penetrations and at the edges. This is required in lower-probability affected areas.
• Full protection — the radon-proof membrane plus a means of removing radon from beneath the floor. This is usually a sub-floor depressurisation sump (a void or perforated pipework under the slab linked to a vent or a low-energy fan) that lets the gas be drawn off and discharged above the roofline. Full protection is required in higher-probability affected areas.

As the builder you have to establish at design and groundworks stage whether the site is in an affected area and, if so, which level of protection applies — then build it in correctly. Building control will check it. A membrane that's torn during follow-on trades, badly lapped, or poorly detailed around pipes is effectively useless, so the workmanship on the install matters as much as specifying it. Where full protection is needed, the sump and its connection have to be designed so they can be made active later if testing shows it's required.

Checking Whether a Site Is Affected

You don't have to guess. UKHSA, together with the British Geological Survey (BGS), provides radon risk reports by postcode and address. For a small fee you can order a report for a specific property or plot that tells you the estimated probability that the building is, or would be, above the Action Level, and — crucially for new work — the level of protective measures BR 211 requires for that site.

The free online maps are useful for a first look at whether an area is affected at all, but for a build you want the address-specific report on file. It's the document that tells you whether you need none, basic, or full protection, and it's worth keeping in the project record to show building control how you arrived at the specification. For existing properties, the same report tells a homeowner whether they should test.

Remediation in Existing Homes

If an existing home tests above the Action Level, there are several remediation options, and they're worth knowing so you can advise customers sensibly:

• Sealing gaps, cracks and service entries in the ground floor. On its own this is rarely enough, but it supports the other methods by reducing the easy entry routes.
• Positive-pressure ventilation — a unit, often loft-mounted, gently pressurises the house with filtered air so radon is pushed back out rather than drawn in. Effective for moderate levels and relatively unobtrusive.
• Radon sump (active soil depressurisation) — the most effective method. A small void is formed below the floor slab and connected to a fan that continuously draws radon-laden air from under the building and vents it safely above the roof. This is the go-to fix for higher levels and the most reliable way to bring a home well below the Action Level.

Whatever method is used, the property should be re-tested afterwards to confirm the level has come down. A sump that isn't pulling properly, or a ventilation unit that's switched off, gives a false sense of security.

Quick Reference: Radon Requirements by Scenario

Why This Matters for Your Trade

There are four good reasons to take radon seriously. First, it's a legal duty: as an employer you have to assess workplace radon in affected areas, and as a builder you have to meet the Building Regulations on new work. Second, it's a genuine health issue — for you, your team and the people who'll live or work in what you build. Third, it's about building control sign-off: get the protective measures wrong on a new build and you risk failing inspection.

Fourth, and often overlooked, is the ability to advise customers properly. A builder who can explain why a plot needs a radon membrane, or who spots that a cellar conversion in Cornwall ought to be tested, looks like a professional. Getting it wrong is expensive: retrofitting a radon barrier or sump into a finished building costs far more than designing it in from the start, and a membrane damaged by follow-on trades may mean lifting a floor that's already down.

England, Wales, Scotland & Northern Ireland

The Approved Document C and BR 211 framework described here applies to England and Wales. Scotland and Northern Ireland have equivalent arrangements under their own building standards — Scotland addresses radon through the Scottish Building Standards technical handbooks, and Northern Ireland through its Building Regulations technical booklets — but the underlying principle is the same: in affected areas, new buildings need radon protective measures appropriate to the site's risk band. Workplace duties under the Ionising Radiations Regulations 2017 apply UK-wide. Wherever you work, check the rules and the radon map for that specific nation and postcode.

Keeping Track of the Work You Win

Specialist compliance work — radon surveys, sump installs, membrane jobs — often comes in through word of mouth, your website, or a local search. It's worth knowing which of those channels actually brings in paid jobs so you can put your effort where it pays. Keeping a simple record of where each enquiry came from, which Trade2Base is built to help with, makes it much easier to see what's growing your business and what isn't.