Damp issues in flat – problems with tenants?

You've fixed the cavity bridging issue at your level, but there may be problems above. Damp in walls is carried by gravity until it hits the DPC at the bottom. If the outer leaf of the wall is saturated, the inner leaf can't breathe even if cavity is clear, so all 'environmental' moisture is trapped.
If there was a guttering issue that was fixed, say a year ago, the damp in the wall might have only just reached ground floor. Some brick types soak rain more than others, I sometimes use a silicone based spray treatment for walls (one that still allows the wall to breathe) facing the prevailing weather to reduce how wet the outer leaf gets. Once a property is really damp, the only real fix is to, after addressing the root causes, let it stand empty and well-ventilated through an entire summer.

Reply to the comment left by LMitchell at 20/09/2023 - 09:43
Interested in PIVs dropping EPC ratings. Could you explain why a PIV would drop the EPC rating? What have your surveyors told you? Many thanks.

Anything such as a bed, wardrobe or other clutter touching or near external walls prevents air circulation, so it is out of order for the tenants to persist in doing this, assuming it is the case.
We have a few PIVs and they are successful, as they continuously push air through the property and are more effective than anything else in our experience, so I'm surprised to hear that a professional recommendation was NOT to install them. Ours also have a heater setting for extra cold spells, meaning really cold air is not introduced. The cost is a difficult one, obviously due to the general ban on tenant expenses- for a hard wired unit in this instance.
We are stating in a new AST that we will pay the tenant £60 at the commencement of the contract (which is in excess of the manufacturer's running cost estimate) in return for them agreeing to use the funds to cover that smallish element of the overall electricity bill. We would also explain this requirement to any new tenants when viewing.
Perhaps the reason for possible negative EPC rating for PIVs is the presence of colder air causing thermal inefficiency, but that is crazy, as you are investing in a remedy for the comfort and health of your tenants.

I think you been a responsible landlord and have done all that you can to remedy the situation. It would appear that the cause of the problem are the tenants themselves, sorry Mr Gove.
I would immediately issue an S21 eviction notice whilst you still can. Get them out of there and then reassess any further works. The longer those tenants remain the more damage and stress and expense they will cause.
You can’t fix stupid.

Bathrooms especially use envirovent cylone, through them or buy 1 yrself. Works with the atmosphere so needs no tenant input. They're magic!

Rather than a PIV, have you considered HRV, Heat Recovery Ventilation? This recovers heat to warm the incoming air while removing damp air. I had one on my home for many years and was very happy with it. It also improved my EPC when I came to sell.

I would highly recommend installing Greenwood CV2 extractor fans in the kitchen and bathrooms as well as Passyfier vents in all other rooms you can fit them in.

Both products are absolute games changers when it comes to condensation and mould problems.

Are you keeping in good communication with your tenants? Have you or those who carried out the surveys pointed out to them exactly what is causing condensation and what they can do to remedy it. Eg tumble dryer, drying clothes, failing to heat or ventilate.
I'm surprised there wasn't already an extractor in the bathroom. Do they have an outside space to dry clothes in?

With the mould, I recently met a council/mould expert who said cutting a lemon in half, adding salt and rubbing it on the affected areas kills off the spores (I haven't tried it and have no idea if it works).

If the dehumidifier is collecting water from the walls then it's a different issue, but I would imagine that would have been picked up by the experts.
If there is water on the inside of the window panes, then condensation is the issue, and adequate heating and ventilation is needed.

Reply to the comment left by W Josef at 20/09/2023 - 11:45
This was as a result of my recent EPC. The assessor told me that they 'hammer the EPC' & gave me a low E rating!
I challenged him on it and after a week he revised it up to a D which is inline with my expectation.
The assessor referred to it as a 'mechanical ventilation unit'. After educating him more on a PIV and questioning whether this was the same as a 'mechanical ventilation unit' he then agreed they were different, and upgraded my EPC.
So, long answer, but it may not be true that PIV's reduce the EPC, it may have just been a case of my assessor getting it wrong or not understanding them.

Reply to the comment left by Paul Baker at 23/09/2023 - 12:09
Thank you that's helpful. The tenants in one of my properties is eligible for free external wall insulation under the ECO4 scheme but the property needs to be an E. The last time I had an EPC done it was a D but have since installed a PIV. So hoping the assessor sees it as a negative and pushes it down to an E.