Fix for condensation inside single-skin wall house

I have some houses like this. As previously stated, insulation was of key importance. I built a stud internal wall, put a membrane in before adding insulation, then boarded & skimmed. To reduce any potential from other damp ingress, I also sealed the concrete floor with liquid dpm. To add to the belt & braces approach, the plaster was sealed with Zinsser Guardz, before topping it off with a PIV. The result is as I wanted it to be. Its a lot of work, but worth it. Each part does a little. We need to remember that these old houses were built with wooden windows frames, housing single glazing. They had no draught exclusion, no central heating, chimneys that supported use of a fireplace in more than 1 room. The concept of a shower, bath, central heating, inside loo & gas / electric cooking wasn’t even a dream back in the day. We can’t expect an old property to perform to modern standards without modern corrective interventions. Sorry, its a big job, but that’s how you bring old property to meet modern expectations.

Hi John39, I have had similar problems with only the mention of compensation from time to time! My property was built in the 70’s with double glazing, cavity walls with insulation etc etc. I provided a dehumidifier and advise the tenant continuously that ventilation is necessary particularly when a tumble drier is active. There are 3 extraction fans (kitchen and both bathrooms) which are usually switched off and after 1 year he has realized that trickle vents should be kept open. Unfortunately after the first year with mould being allowed to establish I have resigned myself to the fact that the house will need to be redecorated when this tenant moves out.


We had a similar problem in our 30 yr old rented out flat. It arose when there was a family of 4 and I confess I was horrified when I saw that there was mould on a child’s bed. It’s all very well telling them to keep the windows open and the heating on and put the washing outside, but they just don’t; and the root cause is the way the property has been built. We got in Envirovent, they installed a ventilation system, and we’re delighted with the enormous improvement. However I’d think twice about letting this flat to a family again!

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We had mould and condensation issues in our flat (converted from office into what looks like single wall flat). Mould was a pain in the back side despite the opening the windows and heating etc. Bought 1 small electric dehumidifier into each room - problem gone! No scrubbing the walls ever since. Heaven.


Thanks. Dehumidifier seem tot way to go temporarily.


I issue a condensation and mould advice leaflet at start - and if I think needed, a cheap window scoop or window vac, and a dehumidifyer, in addition to bathroom extractor on overrun, plus a washer dryer and sometimes a condensing tumble dryer.

If mold visible on inspection, I then demonstrate how to wipe it away using black mould killer.

I have 1 property fitted ith environment which cured the problem there.

It seems excessive, but I find it helps!..

Asking tenants to have windows open during cold winter months is just unrealistic , you may as well ask them to have cold showers too. Drying clothes outside ? - it it’s too much like hard work to be doing that then constantly looking out of the window for the appearance of dark clouds. Not turning extractor fans off ? Have you heard the noise some of them make just when you are trying to sleep. They can be like having a tractor in your house .I’ve turned some of mine off at home and the others I’ve adjusted to be on for such a short period that they are probably useless anyway.
My advice is forget all this boarding this and insulation that you are just delaying the inevitable so start selling your old properties and buy much newer stock . I’ve just sold an old one for £215k getting £950 pcm and with that money I’ve bought two modern two bed ,2 bath flats ( built just before the crash of 2008 of course) for less than what they were originally bought 14 years ago and they get £1400 between them . EPCs are both mid range of C and it’s the stricter EPC regulations that will be your biggest problem with 100 year old properties not a bit of mould as a rental will need a C rating within a decade .
These modern flats are built to a very high spec and include extractors in the bathrooms that are very quiet and centrally run through a ductal system so can’t be turned off . If they put a clothes airer in a bathroom and shut the door this system dries the clothes very effectively so no need for tenants to drape stuff over heaters or use tumble driers.

Interesting comments, thank you.
Well done on converting to a good deal - £215k for two modern two bed ,2 bath flats £1400. 7.8% Yield is good.
Stay well.

I wish it was such a good yield but with leasehold flats there is the dreaded service charge and ground rent that eats into that yield . It’s usually equivalent to about 2 months rent . The upside though is much less maintenance as all electric so less phone calls on bank holiday weekends and like I said peace of mind about future EPC legislation .


Agree, dreaded amount of service charge and ground rent = about 2 months rent.
And WE get called money hungry Landlords!!!


In some of the places with gated development and all gym facilities etc service charges more than 2months rents.

I was told in past by a few tenants that landlords make money from them do I just said why don’t they become landlords and make money too if it was that easy.

I have already decided to sell as no help or protection for private rental sectors for landlords.


Do the windows have air bleeders? If not, then thats an easy fix and along with internal insulation should resolve it.

A lot on my 100 yr old houses have brick vents at floor level, there to furnish open (coal) fires. A lot of people block them off when centrally heated. I have taken advise from builders on this when blocking off the chimneys etc and researched and its not clear block or no block. The No-blockers say it will cause damp. So, I have blocked chimneys and all bar 1 of vents (under floor) in each and no issues have been had. Ie small unnoticeable ventilation is present through floor out window air vents. I have just bough my own home 1920’s build much extended - and may have to do the same here too - though its much much bigger than my 2 bed terraced BTL’s - and also internally insulate some areas.


U are right about opening windows. Had same problem…family drying clothes inside no windows opened big problem… it took me two week to prove to them payed for them go to laundry .Soaked up the condensation first… open window slightly wen they showered ect . In the two week I did this with them windows stayed dry no mor condensation…


1 read the above esp the damp leaflets
2 make sure you have a 100mm vent for tumble drier
3 insulate inside walls with 50mm polystyrene backed plaster board, done this lots of times it works a treat plus improves epc rating
4 give them squeegees for the shower it saves 1/2 cup water in the room every time
5 get a constant running fan not necessarily envirovent and put it in the bathroom put the isolation switch up high, if its a pull switch leave just two inches dangling
6 get them to ventilate in summer big time
7 emphasize no drying of clothes on radiators
8 check there are no building causes for the damp, gutters, internal pipework leaks, roof compromised
hope this helps

These windows are old factory style crittal windows.
It’s a warehouse conversion and grade 2 listed.
No windows don’t have air breeders.