Difficult to heat room - PIV? Internal wall insulation?

sjb266

Hi everyone,
I have a ground floor flat which is part of a set of four - two ground floor, two first floor. I have problems with condensation and mould in the second bedroom, due in part to the room being difficult to heat to the same temperature as the rest of the house and also to lodgers living badly in it. I'm wondering about getting internal insulation for it, and have also been advised to get PIV instead. The room currently has an extractor fan fitted three years ago under professional advice. It is a cavity wall construction.

I'm sorry this is a bit of a long story!
The layout is: my front door on the west facing wall with lounge to the left and the lodgers' bedroom to the right. The bathroom is straight ahead with my bedroom to its left and the kitchen to the right. Between the kitchen and the right-hand bedroom is a set of stairs leading from the outside to the flat above.
The lounge and my bedroom are attached to the adjacent property. The lodgers' bedroom therefore has two external walls facing west and south, whilst the internal walls are adjacent to my hall and the stairs for the upstairs flat. The upstairs neighbor often has his front door open, though much less so in this cold weather. It has always been harder to heat that room than the rest of the house, as it's often a couple of degrees colder. This makes it really hard to heat the whole house nicely as either that room is too cold or the rest of the house heats in fits and starts, getting too hot and then too cold.

I originally had a problem with the room back in autumn 2018. My lodger and I had moved in in July 2018. By the end of autumn, there was mould on the external walls behind the furniture, and on the chipboard backs of the furniture.
I got rid of the affected furniture and got a couple of specialists to look at the room. They said that whilst it would be a harder room to heat given its location in the property, the fundamental problem was lifestyle - my lodger drying her clothes in the room, and inadequate ventilation as she kept the door closed. It was recommended to fit an extractor fan to remove the moisture from the room. I also fitted thermaskirt to help the room heat more evenly and more easily, and keep the walls warmer.
My lodger never complained but when she left it became apparent that the room was still a bit cold and some mould had recurred. However, she did have a tray of what looked like dried meat on top of the wardrobe... and also kept her bath towel in that room.
That lodger left in Feb 2021 and new lodgers moved in in mid Sep. They are a couple. By the start of December both external walls had mould, with the south facing wall especially bad and all-but completely black. All the furniture had mould, including varnished surfaces. It turned out that when I took my lodgers' washing out of the machine in order to do my own washing, and put theirs into a bag outside their door for them to hang out to dry, they hadn't done so. So there were several bags of damp washing in the room, plus a soaked mouldy towel that they'd used to try to wash off the mould. The room was also a mess and they never opened the curtains and they also kept the door closed and rarely went out. However, until shortly before I discovered the mould they had often had the window open as well as the extractor fan being present.
I sorted out all their stuff and tidied the room and cleaned the walls. I had to keep the windows open to ventilate whilst I cleaned so whilst I was in there the room was always cold. I checked that the thermaskirt was on max and also turned up the boiler from 45 degrees Celsius to 65 (I much prefer long gentle heat, and have always been able to heat the rest of the house beautifully like that) With the room tidy, another professional came to look at it. He said the walls were warm enough but that having an extractor fan was crazy and instead I should put in PIV. He had a device that measured humidity which gave a reading of 95% but I don't know if he was measuring moisture on/in the walls or in the air in the room. I brought the dehumidifier back in, and it didn't show anything like 95% when I turned it on. Maybe 80%+, but quickly dropped to the 60s.

I am shocked that the room managed to get so mouldy so quickly, and so was the professional.
My lodgers have been given notice to leave by 15th January and at that point I will have more freedom to investigate how best to heat the whole house. Currently, the thermostat is in the lodgers' room to make sure it is warm enough, as, whilst initially they told me the room was warm enough, after I discovered the mould they told me it had been cold.
With the boiler set to 65, the result is that the rest of the house heats in fits and starts, and gets cold in between. But there's no point turning up the radiators in the rest of the house if the boiler isn't on because the lodgers' room is warm enough; and if I turn them down because they're unpleasantly hot and I dislike the feeling of being blasted with heat, then of course the rooms will cool down even quicker when the boiler does turn off.

When I booked the professional to come, the suggestion over the phone was that internal insulation could be beneficial. Then a different person viewed the property and suggested PIV.

My personal preference is thin internal wall insulation like aerogel or corksol on the two external walls but I'm very worried about whether mould might get trapped behind it, or whether it's suitable for a cavity wall, and the likelihood of mould growing back on top anyway. I'm also concerned about the implications for the flat above or any other junctions between TIWI and walls that don't have it.

But in general I like the idea of that room having a little extra protection to counter the fact that it has two external walls and isn't easily able to absorb heat from the rest of the flat due to bring separated by halls or stairs.

Does anyone have any thoughts? I'm struggling to understand some of the advice on the internet and am also concerned that I'm receiving conflicting advice about what to do with the room and what the problem is.
Should I be treating the heating of the room as a separate issue from condensation/mould/ventilation? So TIWI could help me ensure that room feels warm and I can heat the whole house evenly and gently to a suitable temperature; but I'd still need to do something like PIV to help with ventilation?

I appreciate it may be difficult to advise until my lodgers are out and I can play around a bit more with my heating, but perhaps there are others here who've put TIWI into individual rooms and can advise on the risk of mould or of creating problems elsewhere?
Also I've heard bad things about PIV as a solution.

Thanks to anyone who has any similar experiences or an advice to share.

Doozergirl

I agree that an extractor fan was a ridiculous idea.  It's too much ventilation and no one is realistically going to turn it on in a room that they live in.   

Do you have a thermostat and TRVs on the radiators?  Is it a decent/correctly sized radiator in that room?    It seems to me that you want to be able to balance the radiators in the other rooms so that they run cooler than the one in this room.  

Having south and west walls doesn't strike me as a room that should be hard to heat or be particularly susceptible to mould.  

Yes, you want the house evenly heated so that the walls are warm and not cold to the point that water is capable of condensing on it, and yes you want decent background ventilation and air movement so that the room isn't excessively humid.  

What is around the room outside?  Where does the mould appear?  It's possible that there is some damp getting in.   Also do you have trickle vents on windows?  Double glazing?  How old is the house?  

PIV isn't a bad solution, it's
just often cheaper to maintain the balance in a more conventional way - warmth and background ventilation.  In our first flat we solved the problem entirely by opening up the fireplace that had been closed off.  Having a traditional fire was a more attractive solution for us as well.  

tacpot12

PIV systems can be very useful with eliminating condensation, but you need to know that they can be perceived as producing cold drafts. While you can get heaters to fit them, tenants may try to disable the PIV if they are worried that it will cost them money. Ideally the heater should be thermostatically controlled so that it only introduces air that is warmer than that already in the flat. PIV systems also need vents so that the moisture-laden air can be forced out.

FreeBear

Having done internal wall insulation on one room (north facing, two exterior solid brick walls), it has made a huge difference - Can now heat the room up with a small radiator, and no longer have condensation on the walls. I've lost about 75mm on floor space, but that is a small price to pay.

Have also had a pair of lodgers that spent most of their time hidden away in one room - High humidity and mold was a constant issue. Coupled with other reasons, I wouldn't have another pair. Just the one lodger, preferably in employment or a student. Much easier to keep on top of humidity levels.

As for insulation materials, Aerogel is hideously expensive, a very good insulator though.

Just had a quick look at corksol - Plenty of warm & fuzzy platitudes extolling the virtues of the product, but zero technical information. On that basis, I'm highly sceptical of their claims.... That said, cork is a good insulator with a r-value of 0.038-0.040 W/mK, but not the top performer. Compared with Aerogel (0.014 to 0.015W/mK), Celotex/Kingspan (0.022 to 0.025 W/mK), or fibreglass (0.035 W/mK), I don't see how a 6mm coating is going to do much. If you are spending money on insulating a wall, you may as well use a proven product and base your decision on real world data - For my money, I'd go for 65mm insulated (PUR/PIR) plasterboard and put 25mm or so around the window reveals.

If you really want a thin internal wall insulation at an affordable price, you may as well slap on a sheet or two of Wallrock - Whilst it may reduce the problem of mold, it isn't going to do much to make the room easier to heat (nor will 6mm of cork).

Edit to add - The r-value mentioned above, is a measure of thermal conductivity. The lower the number, the better. You will often come across the use of u-value - This is a measure of thermal resistance which is a product of thermal conductivity (the r-value) and the thickness of the material. So, for a given thickness of material, something with a lower r-value is going to perform much better than a higher r-value.

[Deleted User]

Short hijack here, apologies OP

 @FreeBear did you also have cavity wall insulation there too ?

FreeBear

Catsacor said:

Short hijack here, apologies OP

 @FreeBear did you also have cavity wall insulation there too ?

On the lower half, yes. And to be honest, it has made zero difference in helping to keep the heat in.

Why just the lower half ? - This property was built on the cusp of cavity walls being standard. As a result, the ground floor is cavity, and the upper half, solid 9" (230mm) brick & render.

sjb266

Thanks everyone, that's all really helpful.

@FreeBear, I agree that two people shutting themselves in a room is a terrible idea. That's partly why I've given them notice to leave - I don't want to continue with two lodgers and will only have individuals in the future; preferably ones who will be out part of the day rather than constantly in.
I'm looking at Thin internal wall insulation options because with the room having thermaskirt and one of the external walls having a chimney breast, it could actually end up quite a bit of work to remove the thermaskirt and shorten six individual ends of thermaskirt. Also, the room is only about 3.2x3.2m so already feels a little small. And any option that can be put in by a competent DIY-er (AKA my dad) is a good option, and more so if skirting, plug sockets, light switches etc don't have to be taken off and then put back on.
The Wallrock option looks good. The room doesn't necessarily need much insulation; just a little bit might be enough to make it easier to heat. Another option is to save up money over a few years and then put aerogel in - I don't need a lodger in terms of income; I just want to use the room to help people who can't afford a decent place otherwise if e.g. they're on sickness benefits. Unfortunately it turned out that two such people didn't work, and not just because of the mould in that room. So it might be that I wait a bit before taking in any new lodger.

@Doozergirl the issue is more that there are two external walls for that room, as opposed to their specific aspect. Also, the internal walls of the problematic room are next to a hall and a stairway so aren't quite as 'internal' as e.g. the wall between my lounge and my bedroom.
The extractor fan was certainly on permanently with my previous (single) lodger and the room did get a bit of mould, but I don't think she had a window open and the door certainly wasn't open, so there wasn't much airflow opportunity. When I discovered the mould this time, the extractor fan was on, so I think the lodgers did have it on all the time. It just wasn't enough to combat the level of moisture they managed to produce. But then if you're going to have multiple bags of damp washing plus two people who almost never leave the room (one is on sickness benefits; the other a student but hasn't being going in due to MH issues).
I have been advised to have the fan removed and blocked up as otherwise it's like having a window constantly open. It will also let in my neighbour's smoke and general noise from the outside, which won't be much fun for anyone using that room.

@tacpot12 a cold draft doesn't sound much fun! I might ignore the PIV suggestion on that basis. It's only a small flat and I don't have problems with the other rooms - just with lodgers who shut themselves away and don't come out all day!

markin

I would not block up the hole, just change it to a heat recovery vent, you can't trust people not to close window vents or turn off a dehumidifier. With the use of wago connectors it's a lot easier to extend sockets and switches now safely.