Most people test for radon once, get a reassuring result, and never think about it again. It's an understandable reaction, but it misses how radon actually works.
Radon is a colourless, odourless gas that seeps continuously from the ground beneath your home. It's the second leading cause of lung cancer in the UK, and for smokers or ex-smokers, that risk is significantly higher. The danger isn't a one-off spike; it's the slow, invisible accumulation over months and years. Levels shift with the seasons, with changes to your home, and with the ground beneath it. A result from a few years ago may not reflect what's happening today.
This article explains how often to retest, when to act sooner, and the practical steps for retesting after mitigation so you can confidently monitor and manage radon in your home.
The short answer: You should test for radon every 2-5 years, depending on your previous result, and within three months of any mitigation work.
The two numbers you need to know: According to UKHSA guidance, the UK Action Level is 200 Bq/m³, remediate if you're above this. The Target Level is 100 Bq/m³, the goal after any mitigation work.
Your Retesting Schedule at a Glance
Your previous test result is the starting point for everything. Use this as your quick reference, then read on for the triggers that mean you should act sooner.
| Previous Result | Action | Retest Frequency |
|---|---|---|
| Below 100 Bq/m³ | No action needed | Every 5 years |
| 100–200 Bq/m³ | Remediation strongly advisable | Every 2 years |
| Above 200 Bq/m³ | Remediate immediately | 3 months post-installation, then annually |
The 100–200 range isn't a safe zone. Cumulative exposure at these levels carries a potential health risk; don't wait until you hit the Action Level.
Watch: How radon testing works - passive vs real-time measurement explained
Retest Sooner If Any of These Apply
Certain changes can shift radon levels regardless of when you last tested:
- Home Improvements: New insulation, double glazing, or central heating changes how air moves through your property
- Major Building Works: Extensions, loft, or basement conversions disturb the ground and can open new entry points
- Moving in: Previous owners' results may be outdated or cover the wrong floor level. It’s wise to retest in your first year. If you're mid-purchase, a real-time survey is often the only practical option, given the time constraints
- New Boiler or Ventilation Changes: Affects internal air pressure and how radon enters the building
- Working From Home or Increased Occupancy: Exposure risk rises even if levels haven't changed
- After Fitting a Mitigation System: See the section below
- Landlords: A change of tenancy is a trigger, too. Every new occupancy is an opportunity, and increasingly a point of legal prudence to verify levels.
When it comes to testing, you have two options: a three-month passive test or a real-time measurement survey.
Post-Mitigation Retesting: The Step Most People Skip
Most homeowners who fit a mitigation system never retest. However, fitting a radon sump or ventilation system does not mean the problem is solved - it means the solution is installed, which is different. At Better Indoors, verification testing is built into our process as Step 4: Assessment, Design, Installation, and then Verification.
- Test Within 3 Months of Installation: The only way to confirm the system is actually working.
- Fans Can Fail Silently: No alarms, no visible signs. Radon doesn't smell. Testing is the only check.
- Test Annually After That: Systems degrade, and soil conditions change over time.
Are levels still elevated after installation? The system likely needs adjustment, not replacement. This is common and why professional follow-up matters
It's also worth knowing that a sump alone isn't always the best solution. In many cases, combining sump extraction with positive pressure ventilation delivers better and more reliable results. A well-specified system from the outset means fewer problems at the verification stage.
Why Levels Change
Radon is produced continuously; there's no fixed supply that runs out. Levels shift with atmospheric pressure, soil moisture, and the seasons. Winter is typically worse, as sealed homes and heating systems create negative pressure that draws radon up through floor joints and service gaps.
The UK Health Security Agency’s interactive map lets you search by postcode using the national database of real measurements. This is worth checking before you do anything else. Note that elevated levels can and do occur outside designated high-risk areas.
Watch: How radon enters your home and what you can do about it
For Landlords and Property Managers
If you're managing multiple properties, retesting can't be something you get around to eventually. The stakes are too high, not only for your tenants' health but your own compliance, so you shouldn’t leave it to chance.
- Any basement occupied for 1+ hour daily should be tested, regardless of whether you're in a radon-affected area like Bath.
- Awaab's Law and increasing regulatory scrutiny around indoor air quality make proactive radon management a legal obligation in the making, not just a health one.
- Make retesting part of your pre-let checklist, as it protects tenants and your legal position.
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Don’t Let Your Test Gather Dust
Radon levels change, and so do the properties we live and work in. A single test isn't a permanent guarantee; treat retesting as routine maintenance, not a one-off task.
For homeowners, staying on top of retesting is one of the most practical things you can do for your family's long-term health.
For landlords, proactive retesting protects your tenants and your compliance position as indoor air quality regulation tightens.
With extensive experience in radon testing, Better Indoors delivers real-time radon measurements across the UK. Schedule your appointment today.
