Fix for condensation inside single-skin wall house

Hi fellow Landlords.
We have typical 100 yrs old 2 up, 2 down, 100 yrs old terraced-cottage house in home-counties-market town setting. Done out modern/tasteful…you get the picture. But ultimately still single skin wall house.
We have had a family rent for a year, perfect in every way, rent paid on time, etc. But we have condensation problems. I have told them to keep double glazing windows very slight open, but No, they believe open windows give children pneumonia.
I do not want to ask them to find somewhere else, ultimately they are nice folks, he religiously whips down condensation/mould every Sunday, etc.

Has anyone got any practical solutions or fixs please.

I would advise dealing with structural issues, ensure adequate radiators in each room and humidity sensor fans in kitchen and bathroom. We have provided a PIV unit but if the tenant fails to heat the house or doesn’t follow lifestyle advice you will always get mould ( doesn’t matter what the companies say)
The local authority are very helpful if your tenants don’t listen

There may be cold spots in the room. Ventilation is essential and it’s not an option for him to refuse. Windows could be opened during the day when children are not in there. How do they dry their clothes?

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You need insulated walls… A humidity sensitive fan that automatically comes on and is not controlled by the tenant… Ventilation is Essential


when you say single skin house you probably mean double layer brickwork ,but with no cavity ? A single skin is only 110 mm thick Many houses are solid walls, if older stock. .Thus a cold wall promotes condensation , esp. bathrooms and kitchens. Even a cavity wall without insulation can be a problem

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Old properties don’t usually have enough space for cavity wall insulation.
I would advise against external wall insulation if the external construction is engineering brick as the property needs to breath. Our LA have removed it off properties that were old terraces as it exacerbated the mould problem
I have not used internal insulation on old terraces as I have found (and heard the same from others) that the smell of mould does not disappear.
Regarding insulating the roof be careful if you have old bitumen felt as this is non breathable and you will end up with condensation in the loft space. You will need vent tiles in the roof ( you can get leaks with those though).
Check that the pointing does not need addressing.
Check the silicone around windows has not degraded or shrunk and does not need replacing.
Make sure you don’t have any roof leaks or rising damp. The moisture from rising damp contributes significantly to condensation. I use Rentokil for surveys.
The LA are happy to advise you if things need doing.

I mean insulate the walls INSIDE. I have done this on some of my places and got a great EPC. I would NEVER insulate a house on the outside. It does not have to be 100 mm PIR it can be 25mm PIR with plasterboard glued to it. It works… with humidity fan. Took a lot of effort, but no probs. Do not dry clothes indoors

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A family in what sounds like a small house is generating a lot of condensation.
We had tenants fill a bathroom with mould simply because they were not heating and ventilating the place. (no mould caused by previous tenants) We put in an EnviroVent fan, which I believe does the same job as a PIV unit.
It’s hard wired into the electrical system so they can’t turn it off. I think there was also the option of having a larger unit in the loft which was meant to serve the whole house.
However, they do still need to open windows in addition to anything else.
Our tenant sent photos of the fan dripping with water as still she refused to let air in so there’s only so much it can do.


when a fan is fitted it has to have an isolating switch/ fuse nearby. So they can turn it off.! Stupid regulation. !!

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The fan extracts moisture. It does not ventilate like a PIV unit.
We have installed both and still have tenants report the water dripping off the fan.
I called out Envirovent. It was because the internal house temperature in the house was 3 degrees C!! It was 4 degreed C outside.
They did not heat the house and so when the tenants showered it could not keep up with the moisture (and that was in the presence of a PIV ad trickle vents on all the windows).
It’s worth calling them out as they will write a report and it will cover you.
I will not use Envirovent again as despite installing the products (they guaranteed mould free whatever the tenants did) we ended up with mould. Their products require regular maintenance. PIV filter washing circa yearly or bathroom fan requires washing every three months. I would not leave that to the tenants as it is too expensive a product and I don’t need the headache of the maintenance regimen. I was fed up of the overpromise of the product. They don’t honour their guarantee. I reported them to Trading Standards.
Greenwood have a range of humidity sensor fans that are cheaper and don’t require regular maintenance.
Sounds like the tenants are not adequately heating the house.
Take photos of rooms (distance of furniture from walls, clothes on radiators, temperature of house)

Mould is a complicated issue and I have learnt to deal with the structural issues as my priority before I blame the tenant. Often it reduces the problem.
But the tenant lifestyle is important. We have a lengthy section in the contract with clauses referring to those in our LA leaflet. How to heat the house using the room thermostat rather than the timer, location of furniture, drying clothes etc

We had trouble with EnviroVent too. Ended up getting it half price but they said a load of rubbish. Anything to sell something.
They told us to install their device first which would stop the mould growing and diminish it then remove it with a solution.
This didn’t work (of course!) as no device can clean off mould already present. But anything to get the sale through as quickly as possible.

We were going to take legal action as we spent £10K about 10 years ago across the portfolio. When we spoke to trading standards we were told that although we had all the evidence there was no guarantee if we went to court ( judges are unpredictable) so I was advised against it. In one property we changed the cartridge every 3 months. Nothing ever lasted. There sales pitch was Bravo Sierra.
We spent six months communicating with the MD of Envirovent (he was useless) we posted every day on social media just to get someone out to the properties). We recorded the conversations and the chap they sent out admitted surveys were wrong installations were wrong. They always blamed the tenants.
However I note that their sales manager and our area franchise manager no longer work for them. They allegedly left ( sure, whatever…). They also deleted my posts on social media.

I have not given them a washing machine, not a drier. So assume the dry the clothes in doors on a clothes horse of similar.
Of course adding to the humidity.

Enviromental Health our way are useless, they are only interested in successful easy prosecutions. if you refuse to roll over, they go away.

I have been renting out a terraced house for 20 years. I have found you get condensation/mould with some tenants, but not with others. It all depends on the tenants lifestyle. They should always open the windows at some time during the day summer and winter, and not dry clothes on the radiators during the winter.

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Thank you Roger4, sensible suggestions. But short of moving in :-(, cannot see being able to enforce this.

As others have said, you could explain to them the seriousness of mould to your property and their health of course, and point out it wasn’t there before. Get a leaflet from the Council.
They should at least have a dehumidifier but again, hard to enforce.

I have one single skinned walled room in the house - a utility room that in the 1950s might have been for coal storage, connected by an unheated corridor to an unheated kitchen (which is OK as it gets warmth from adjacent rooms).

A couple of years ago, since we were using the room for the attached loo and ironing, we decided to improve it. It was perishing cold in Winter, only a couple of degrees above outdoor temperature. We decided on a bit of a makeover.

We had the walls insulated internally with Kingspan panels. Each panel comprises 2 heat-reflective sides and a highly insulating centre.

The new internal insulation is about 1.5" thick with new plasterboard and plaster on top of it.
So we lost 3" on the width & breadth of the room. There is now a rather low powered radiator in that room, due to the microbore piping.

What we got was, the temp can drop to +10 deg C if it is -3 outside of a night, while the main house is at say, 18 overnight.

Zero condensation now, while in the past this little used room had mould in its extremities at ground level and really bad mould in the cavity behind fitted cupboards.

Were this main living space, it probably still would not comply with some Whitehall-directed EPC thing for buy to lets. But it transformed our utility space for sure and is an indicator of what’s possible without actually building a brick inner skin to a building.



Definitely doable but you’d probably want to do some rewiring and plumbing at the same time, near impossible while there’s someone using the rooms being worked on. If done professionally you’re looking at £3k-£5k per room depending on where in the UK.