Most small business owners treat mould as a bit of an eyesore. A dark patch in the corner of a store room, a musty smell in the back office, something to sort out when there’s a spare afternoon.
The real cost shows up later, and it’s rarely just the price of a tin of paint. Follow along to see where the bill actually lands, what the law now expects of you and when it’s time to stop reaching for the spray bottle.
Why Mould Eats Into Your Profit Before You Notice
The trouble with mould is that it doesn’t stay still. It spreads through plasterboard, carpets and ventilation, and the people working near it start to feel the effects long before anyone picks up the phone to a contractor.
The CIPD’s 2025 Health and Wellbeing at Work report found UK staff took an average of 9.4 days off sick in the past year, the highest level since the CIPD started tracking absence in 2010. If a damp office pushes even two of your team past that average, you’re paying wages for work that isn’t getting done. The NHS links damp and mould to respiratory infections, allergies and asthma flare-ups, with the effects worst on staff who already have a chronic condition.
There’s also the quieter cost of presenteeism, where people turn up but work at half pace because they feel rough. You won’t see that on a spreadsheet, but you’ll notice it in missed deadlines and slower output.
The Legal Risk Landlords Can’t Brush Off
If you let out residential property as a side income, the rules have tightened. Under the Homes (Fitness for Human Habitation) Act 2018, a rented home has to stay free from serious hazards like damp and mould throughout a tenancy, and a tenant can take a landlord to court if it doesn’t. The Act only covers residential lets, so if you’re a business tenant in a damp commercial unit your route runs through your lease and the Landlord and Tenant Act 1985 instead.
Awaab’s Law goes further. Since 27 October 2025 it has forced social landlords to investigate damp and mould within fixed timescales, and the Renters’ Rights Act 2025 will extend the same regime to private landlords, with implementation expected from 2027 once the consultation on timeframes closes. The window for fixing a known problem is about to get a lot shorter.
When DIY Stops Being Enough
A bottle of spray and an open window will handle a small patch of surface mould in a bathroom. Once it keeps coming back, or it’s creeping across a whole wall, the problem is usually moisture getting in somewhere you can’t see.
Once you’re past that point, it’s worth bringing in a specialist who treats the cause rather than what’s on show. An expert cleaning firm like ICE Cleaning will start with the moisture and work back from there, not the stain on the wall. A specialist mould survey isn’t the same as the general building survey you’d get when buying a property. A building survey gives a broad overview of the structure, while a mould survey digs into the damp itself. A specialist contractor will usually:
- Map moisture across walls and floors to pinpoint where water is getting in
- Take air samples to measure the spore levels your staff are breathing
- Trace the root cause, whether that’s a hidden leak, poor ventilation or rising damp
Once they know what’s driving the damp, the remediation holds instead of returning a few weeks later.
How a Minor Patch Becomes a Five-Figure Problem
Picture a small office with eight staff and a slow leak behind a kitchen unit that goes unnoticed for months. By the time the smell gets bad, the mould has spread into the surrounding walls.
Stripping back, drying out and reinstating that section might run to a few thousand pounds on its own. Add a couple of staff taking extra time off, a damp-related claim that nudges your insurance premium up at renewal, and the lost productivity while the work goes on. If you’re also the landlord and a tenant brings a claim, legal costs land on top. A patch that would have cost a few hundred to fix early can easily tip past £10,000 once it’s left to grow.
A Quick Compliance Check for Landlords and SME Tenants
Before the next round of regulations lands, it’s worth running through the basics:
- Log every damp or mould report from a tenant or member of staff with a date and a photo
- Set an internal target for investigating reports, with 24 hours a sensible benchmark for anything urgent
- Keep records of surveys, air samples and remediation work for at least six years
- Check your insurance schedule for damp-related exclusions before renewal
- If you let residential property, diarise the 2027 window for Awaab’s Law in the private sector
Deal With Damp While It’s Still Cheap
Mould is one of those problems where the bill grows the longer you ignore it. Catching it early keeps it a maintenance task. Leaving it turns it into a health issue, a legal issue and a productivity issue all at once.
If a patch keeps coming back or you can smell damp without seeing the source, treat that as your signal to get a proper survey done. Finding the cause now is far cheaper than dealing with the fallout later, and it keeps your team healthy and your books clean while you’re at it.
