In my mind PIV should be illegal and I am going into print on that, not just here - but in a soon to be published book.

The reason is that, yes although it works, cooler, drier air is blown into the home using a fan and warmer damp is expelled through cracks, gaps holes and anything that’s not airtight. The upshot is that the tenant pays for the fan to run as well as for the warm air that is expelled. I feel this is exceedingly unfair as the tenant is paying to warm the planet so that the property is protected.

There is a mention of energy efficiency in the link, I suspect that the writers don’t understand what that means! I would like to have seen it say ‘Energy Use Reduction’

Using PIV increases both ventilation and energy use, We need to decrease energy use

Cheers gents, having read the document more carefully and some of the annexes , it would appear i leapt before looking. Once you get past the politicing in favour of tenants, the guidance is better balanced and the penalties ( as they should) are intended to deal with those who don’t improve properties that are incapable of being warm and dry. So in reality if damp or mould is reported/found , having determined that there are no deffects in the building or its fixtures/ fittings ( and resolving any issues that may be found), it’s down to the landlord to educate the tenant in making the home work as it should and demonstrate that the extraction fans, heating , windows etc work as as intended.

I can sympathise with you to some extent. I have oversight over a Syrian refugee family who were, until very recently, living in a rented 3 bedroom end-of-terrace house probably built in the late 1920's. There were no extractor fans at all and despite my speaking to the landlord about this before they moved in, nothing was done, other than for the latter to suggest that they just "open the windows". This was ok during the summer months but not in the winter of course. The inevitable happened with damp and mould due to condensation forming on the colder surfaces in the house. Eventually the landlord fitted an extractor fan in the bathroom but refused to put one in the kitchen.

The landlord went to the expense of having a damp survey done but then refused to act on most of the recommendations. One of the recommendations was to install a PIV unit which the tenants were willing to use even after being told of the likely financial implications for them, as they were concerned about the health hazards with the current situation (especially for their youngest child who was 5 at the time). The recommendation was rejected on cost grounds.

The surveyor also recommended installing vents with a water vapour permeable membranes in them, (which I had never heard of) but looked like a good idea as none of the uPVC windows had trickle vents. (https://www.permagard.co.uk/perma-vent-standard).These were also rejected on the grounds of cost.

The inevitable result was black mould on the walls behind furniture, on the stairwell ceiling/coving and inside built-in wardrobes on clothes and shoes. There was no question of drying clothes indoors as the mum always used the line when the weather was ok as she was aware of the cost of using the tumble drier but of course she was forced to use the latter on wet days.

The family left the house a few months back as the landlord wanted to sell the house and sent them a Section 21 notice. It was a blessing in disguise. They had lived there for 5 years and took good care of the place, always paid the rent on time and hardly ever complained, despite the mould problem which the mum constantly battled with using bleach. I suspect their energy bills will drop significantly as the new house is smaller, of more modern construction and has PV solar. It also has gas for cooking rather than electric.

I have sympathy for landlords as, IMO, the rights of tenants have swung too far the other way which has prompted the mass sell-off of rental properties and led to large increases in rent due to lack of supply. I would never entertain the idea of becoming a landlord myself unless I was 100% sure that the tenant would take reasonable care of the property and not trash it and then do a runner!

Ventilation in UK house has always been poor - building regs require (noisy) extractor fans which are usually controlled by lights so don't stay on long enough to dry bathrooms even if the residents use them at all. We have widespread use of gas hobs (lots of water vapour) and people don't put lids on pans (more).

We have a climate and small homes with limited outside space which makes it difficult to dry clothes outdoors or have drying rooms that are properly ventilated. So many people are drying clothes on indoor drying racks or hanging on radiators.

Our MVHR is one of the biggest upgrades against previous homes. We're lucky enough to have a laundry/utility room with a 'sheila maid' dryer and the extract from that room to mvhr is overspecced. MVHR has its own humidity sensor and we have them in the bathrooms.

Ideally you'd have heat recovery ventilation/extraction whether single unit or multi room. But failing that if you're using extractors/PIV controlling it using some decent humidity monitors (ie not ones mounted on the extractor fans themselves which have been useless when I've tried them).

How about using some 'home automation' products to better monitor humidity and control extraction? eg https://www.shelly.com/en/products/shop/shelly-plus-h-and-t

If the problem is drying clothes then a heat pump condensing tumble dryer costs more up front but are cheap to run and dry clothes without impacting internal humidity of the house. If there's currently another type of dryer or none at all that might make a big difference

And lastly, what are the running costs and practicalities of Dehumidifiers? https://www.diy.com/departments/vonhaus-12l-day-dehumidifier-24-hr-timer-continuous-drainage-for-damp-condensation-laundry-drying-mould-smell-control/5056115707124_BQ.prd
If you assume the average UK house is leaky enough to for human healthy air changes but not to control humidity from washing etc would they not be a cost effective solution? They're removing the moisture from the air whilst retaining all the heat within the house - they all seem to have a tank but I don't see why they couldn't be plumbed into a drain like an MVHR unit.

I remember as a child my mother doing the family washing in the kitchen with an open tub washing machine with a wringer mounted on the top and a sheila maid dryer mounted on the ceiling to do the drying. (The washing machine might have been a Goblin but I can't remember how the water was heated). All of this was done in the kitchen and I recall lots of condensation on the kitchen walls during and after the washing. I also remember waking up to frost on the INSIDE of the bedroom window. The house was a nothing special South London terraced.

I don't remember there ever being a mould problem anywhere.

So what changed between then and now? Housing fabric, life style or a combination?

I should have mentioned that we bought the family a dehumidifier which they did use regularly but was probably fighting a losing battle in what was quite a large house. There were only 3 bedrooms but 2 reception rooms and all the rooms were large compared to modern standards! You mention overcrowding and this was an argument put forward by the owner. The landlord was aware from the beginning that it was a family of six - two parents plus four children and but argued that the dampness/mould was down to the large number of folk in the house. I am sure this must have contributed to the problem but the lack of ventilation and wall insulation did not help.

The irony was that as an enthusiastic IWI fan I was prepared to carry out some IWI installation myself (my labour would have been free!) but being just a support worker I had no authority to do any such thing. Also SWMBO had vetoed any such activity as it was not my responsibility.

WIA - where do you 10p/kWh from!

ventilation **HEAT** loss

How much do you pay for your heat ?

Mostly heat in homes comes from gas - price cap is currently 6.89p/kWh
Sometimes from oil - 8p/kWh
Sometimes from ASHP - 9p/kWh
Solar gains are free, direct electric more expensive, other options are available..!