Mould after grant funded insulation?

Unless there is a radiator nearby providing a heat source then bay windows in older houses typically solid 9inch walled Victorian houses will condensate. Firstly establish if the outer or inner walls have been insulated. If they have then possibly there is water ingress from poor sealing around windows, compounded by a lack of heat and ventilation. The challenge with older properties is that they were designed to 'breath' through the chimneys, timber sash windows etc, and when we seal them up with good intentions, moisture cannot escape and the excess condenses out on the cooler external walls.. My tenants always assure me they are heating and ventilating however I usually find that thermostats are set to low, it's clear windows haven't been opened in a while, and the radiators are loaded with laundry and so a little re-education is required sometimes to change habits.. A good local builder will be able to help and check for water ingress, but in the first instance though I would contact the insurance provider if you have a 25yr policy...

If your late mum said mould would periodically return, that suggests that this is an ongoing issue and not just caused by the insulation. Mould is caused by poor ventilation/heating. It may be the insulation has aggravated it, but you are clutching at straws if you think the warranty will cover this.

From the images and your description that despite painting over the mould using antimould paint it returns, you are just spreading it about and making it worse by simply painting over it. You need to treat (ie kill) the mould first before you paint over the stains, otherwise it will return and get worse.

The current tenants may ventilate the place, but probably keep the heating on low. Give them a condenser tumble dryer to dry their clothes.

With the recent hike in energy prices, your problem will only get worse. You need to grab the bull by the horn, treat the mould properly, heat the rooms and ventilate thoroughly.

Hello there,

I have a better idea. How about you sell me that property and any other problem ones you have?

Rain is getting in around window ? I would check this out.

Hello Sam. There are several possibilities, I see that you have had replacement windows, it could be to do with those - particularly frame or cill where they meet the masonry, it could be condensation on a solid [cold] wall. If the walls are cavity construction - a little bit early, cavity construction did not appear generally until after the first world war, then the cavity has been bridged - quite a favorite situation when installing any form of cavity fill. I think first step see what type of construction the brickwork to the bay window is, measure the depth of the reveals [the side part of the windows] 9" = solid construction without a cavity.11" = cavity construction and 13.5" is usually a solid wall again. There are other sizes and situations but those are the principal ones. If this seems a bit daunting ask a local builder - who you trust for advice. Depending where it is it could even be rising damp from outside - if for example the flower bed has been raised, or blocked rain water gully. As you can see there are quite a few options but compared with some I have come across it does not look too bad/expensive to sort out..

As mentioned above, houses were built to breath, and modern efforts to plug every draft, and seal every nook and cranny only opens up other cans of worms, and condensation and mould is the result. Looks like it could also be rising damp - given the house is 1890s this may also be the source. Remove the electric socket and if the screws or back box is rusty, then youve got rising damp which will need specialist treatment. If on the other hand is ventilation and cold walls, line them with Wallrock KV600 Thermal Liner. I had a cold corner in one of the bedrooms and since Ive had this installed, Ive never had any mould at all because the wall doesn't get cold. Good luck

What happened to the air bricks when the cavities were filled? These were put in for a reason and there perhaps should have been a vent left in place? Long curtains, not opening windows, drying washing indoors all lead to problems. Even, as daft as it sounds, I am sure that underlay and fitted carpets on wooden floors block off ventilation

Most of the options have been covered in previous posts. You should be aware that the damp proof course on a building of that age is probably a line of slate and these can crack/break and allow rising damp.

I have been pointed to a very effective way of dealing with humidity inspired damp and mould. There is a product called "Passyfier Vents", these come in varying sizes and are not powered in any way. Yet they can 'extract' upto 1.5+ litres of air moisture from a room in 24 hours, (depending on size). They have a membrane in their design so do not cause drafts etc.

Having had major mould issues, from clothes drying, in both a 1970's maisonette and a 1880 mid terrace, I was recommended to fit them, in conjunction with new extractor fans in the kitchen and bathroom. Todate I have found them highly effective and all mould has been eradicated.

I would have thought nothin* to do with the insulation.
For it to have got so bad your tenants are not wiping away with a proprietary anti mould remover; are not ventilating the property; drying washing on radiators or airers; not wiping the condensation from windows in the mornings.
I had this problem caused by my tenants “lifestyle” to the extent they reported me to environmental healthcare. I begged EH to come and inspect the property and they said I had done everything I could, even installed passive air vents in rooms without eco thermostat extraction is kitchen and bathroom (which the tenants turned off) br />
Tenants were not pleased that they were found responsible for the mould and resultant damage.

Meant to add to initial post-when (not if! lol) I have condensation problems I refer my tenants to the links below-handy for all LL'ds....
https://www.yumpu.com/en/document/read/50203638/reducing-condensation-in-your-home-reading-borough-council
https://www.reading.gov.uk/housing/private-renting/repairs-and-maintenance/damp-and-mould/

When info comes from an official body tenants tend to take note rather than when it's me as LLd telling them to heat and ventilate more....