How can I prevent mould in my ex-local authority flats?

It’s most likely a combination of the two, lifestyle and problems with the building.

Old-style bitumen roofing felt often fails near the eaves (water gathers and the felt rots). Eaves protectors can be fitted, preferably before it fails, to ensure any water runs into the gutter).

When the felt fails, rainwater can get into the cavity wall, making any cavity wall insulation wet. Once it’s wet, it stays wet and act water penetrates the internal walls and the wet insulation acts as a cold bridge, transferring coldness from outside to the inner walls.

Condensation forms on cold surface.

Also, poorly installed loft insulation can block the eaves making the loft ‘sweat’. Condensation forms on the underside of the felt and runs down to the eaves. Again, it can get into the cavity. Eaves vents can ensure the loft insulation doesn’t block the eaves thereby ensuring the loft is properly ventilated.

Also, failed pointing can allow the cavity wall insulation to get wet, with the same results.

Of course, we tend to use showers these days. Often twice per day. Showers create much more moisture than a once a week bath created. PIVs, dehumidifiers and bathroom extractor fans (preferably controlled by a humidistat) can help to remove moisture from the air.

So, in summary, damp and mould is caused by many reasons. It’s more often likely to be a combination of lifestyle and building fabric.

New EPC rules will exacerbate the problem as cowboys insulation installers rush to take advantage of unsuspecting homeowners.

In my opinion a great deal can be done by the tenant. In one room I had a tenant, despite explaining the issues to her I had to thoroughly clean the room and paint it twice inside 12 month period. She left. The next tenant came in and I explained the issues to him and he was there two years without any mould whatsoever. Sadly, the building itself is prone to mould but an enormous amount can be done by the tenant.

‘The windows are relatively new’. That could be directly related. Draughts (or at least some air flow) are brilliant for helping to reduce condensation which is needed to cause mould formation.

I believe the regs changed not long back to make some form of air flow mandatory in new window installations. When I replaced windows, the trickle vents were usually optional extras at cost.

I owned similar Victorian terraceds as student HMOs, some with original sash windows and some that had been replaced with non trickle vent uPVC double glazing. There were never any significant mould issues in the properties with the sash windows. In one property that had DG with trickle vents that could be opened and shut, I removed the internal plate from the vents so they couldn’t be closed off.

Also if you have replaced single panes with double glazing, you have lost the obvious cold spot in the room where moisture could condense relatively harmlessly and be wiped in the morning or just left to evaporate over the day and reform on the pane overnight. Then the cold spots become parts of the walls and ceilings - especially corners and behind furniture pushed close to external walls.

That’s not to say there may be another cause/s of course - but from very long experience with many Victorian houses a change of windows can change the whole dynamic of the formation of condensation in those areas; loss of air flow and where the condensation forms.

Also with ex-local London properties we've had patches that attract mold.

As above I suspect a combination of lifestyle and problems with the building structure.

It seems to have become worse with the addition of double-glazing to originally single-glazed windows.

Anyhow, to solutions. It's not a perfect solution but the best we've found so far Glixtone Funghishield https://www.selcobw.com/catalogsearch/results/shop-by/?q=glixtone

But its white or magnolia only

To a lesser extent, mold resistant bathroom paint if you need more colour options

https://www.diy.com/search?term=dulux%20%20bathroom

Both have something in their formula to stop mold growing.

Get some anti-mold spray and teach your tenants to use it. In any case you need to clean the mold off areas before painting the new stuff

I have London property; I can guess the build type you have. I haven't discovered a silver bullet to the mould issue yet, but a few practical steps we take: quality anti-mould paint to window recesses and whole of bathroom; trickle vents kept open; tumble dryer installed; programming central heating to come on each day; vents to external in bathroom and kitchen; eliminating any mould at end of a tenancy (ideally before if possible). And "educating" new tenants about ventilation. On a cold north wall with damp we fitted quality insulation board with membrane and replastered and this made a massive improvement to that property.
Despite all the above, some tenants will seal a property up, air dry clothes, leave bathroom door open etc. etc. and the black stuff soon appears anyway.

Reply to the comment left by Ross Tulloch at 11/02/2025 - 10:00
You illustrate what I found to be true, having Victorian properties let to students over many years with obvious frequent tenancy changes it was a proven fact that groups of four young adults could live in them without any significant condensation or mould issues. But every so often there would be a significant problem in houses which were perhaps at the margin of tipping into problems if lifestyle issues were in play (HMOs with high occupancy rates generally falling into that category).

Mostly, issues were resolved with advice to the tenant/s and some HG Mould spray and new paint. The problem is the odd stroppy parent who would get involved because their little darling couldn’t possibly be part of the problem will be given the final say the way things are heading with the idiotic - landlord as villain, tenant as victim political stance and the replacement of experienced council housing standards officers with those who (from personal experience) seem much less informed on practical matters.

What I find frightening, I have enough knowledge should I wish to do it, to select a perfectly decent home and turn it into black mould central after a couple of months - whilst avoiding leaving any evidence and knowing how to answer any lifestyle questions that would give the game away. It seems very much that if it is impossible to actually prove tenant lifestyle issues (which is very difficult as they are obviously 100% in control behind a locked front door) then the default will be 100% liability upon the landlord. Add in the presence of no win no fee outfits and this will become a serious risk for landlords to consider.

I managed an ex local authority property for a friend who moved away but kept the flat. Mercifully , that flat was repossessed by the council for demolition , so Im no longer in charge of it. He had lived in the flat for a number of years before moving out and in the first five or six years of renting , we had no mould issues whatsoever.
Then almost overnight, we had some quite bad problems. Of course , we put it down to the tenants usage, and brought in the dehumidifiers and educated them. But even our 2 German tenants (who were exemplary in their care of the flat) told us they had a very difficult time keeping on top of it. In the three years they were there, things got worse and even they couldn't keep on top of it by the end.
With subsequent tenancies , it was an absolute nightmare.
I was baffled but then I noticed that the council were keeping the outside of the building beautifully painted and every few years would paint the outside of the building. I had the strong feeling that it was the paint they were using that created mould inside the flat. And that's because there had been no problems for so many years previously; nothing else made sense.
(A darker view is that due to the compulsory purchase , they decided to mould everybody out!)

There was a time when Local Authority homes were well maintained by dedicated teams of in-house staff.

Nowadays, they tend to employ fly by night co tractors that care little about their work.

New windows may well have been incorrectly fitted. That uPVC trim covers a multitude of sins.