Cavity wall insulation is it a good idea or bad idea?

[Moon30]

Is it a good idea or a bad idea? I hear mixed opinions.

The house was built roughly 1920's, so may or may not be suitable, until they come and have a look we're just doing some light research.
We already have some damp, mould and condensation issues. We're on the end of a terrace so lots of outside walls, those are the walls were having issues with. Cold spots where condensation lands, turns to mould and also mould on the back of furniture near by, we don't have furniture pushed right up to the walls and we try to keep furniture away from those walls as much as possible but not always possible in the smaller rooms. The house is cold, it doesn't heat up much in winter, which doesn't help matters. the heating has been on most the night tonight and the bedrooms are still only at 14°c. The house very rarely heats up past 16°c in winter, maybe 17° if its milder weather. We use dehumidifiers, open windows etc nothing helps with the mould. Now because of this I thought the cavity wall insulation would be a good idea but apparently I'm being told by family members it's likely to make the mould and condensation issues worse so they're recommending we don't have it done? Is this likely to happen?

Our home is rented so I guess if the landlord wants it doing, we won't have much say but since we're already complaining about the mould and damp issues I'd like to be a bit more knowledgeable before we discuss it further with the landlord.
Thank you 😊

Insulation and vapor barriers are standard in the US.

If you rent then move to a more modern house. 16 deg in winter is taking the piss.

The answer is, it depends.

The material used, the exposure of the environment and the construction of the walls themselves all factor in to whether or not it is a good idea.

Lots of 1920's building are not cavity, but if yours is, it would be best if a proper risk assessment was done so that the various factors could be considered.

A useful tool to aid in the decision as to wether this installation measure would create the desired result or cause unintended consequences is a wufi calculation, see this explanation: https://ggbec.co.uk/expect-good-wufi-report/

If your walks are kept warm in a way which doesn't cause unintended consequences then internal mould and damp would be resolved/reduced.

Finally if it does go ahead, an installer which is part of this association would be a good idea: https://ciga.co.uk/

You would then have a guarantee.

Current building standards in a different country are not especially relevant to the question as to whether or not there are any technical contraindications to a particular retrofit measure of a house dating from 1920's Britain.

Bad idea. We had endless mould issues after putting it in our last house. Friends have said the same of theirs. Houses need to breathe.

To help you begin to have some more understanding of the issues I recommend you spend some time looking at the videos available from this organisation:
https://youtube.com/@cumbriaactionforsustainability?si=2ak1EhrWV8zbbCZT

It is hard to come by objective advice as most contractors have their own agenda or don't have a complete understanding, being skilled at a particular aspect or method/s.
This organisation provide well informed advice and because their agenda is to assist people in Cumbria with improving homes which are old housing stock (lots of that in Cumbria) because that's a good way for people to save energy, they are not pushing a particular product or service, they are trying to educate householders because when you are informed you can make better decisions for a successful project.

We're trying, unfortunately not many houses go up for rent in our area and when they do there's a long list of applications.
We're saving for a deposit to buy our own but due to some unforseen circumstances this year we had to use some of the funds so building it back up again. We did join the local council housing list too, but they also have hundreds of applicants and not enough housing. So for the time being we're stuck here 😔

Thank you, I'll have a look at those links.

Oh that's not good. Did you have the mould issues prior too?

The way the condensation lands on our walls in certain spots at the moment always makes me think that it's like our house is sweating and can't breathe, so maybe cavity wall insulation isn't a good idea then.

I’m following with interest because I’m considering having cavity wall insulation.

However, if you are renting, your landlord has an obligation to ensure the property is not damp and mouldy. If he’s willing to do anything to the house, I would suggest to him getting PIV (positive input ventilation). I had this in my last house, which was 1930s, didn’t have cavity walls and got very cold, especially on the north walls. It solved the condensation problems practically overnight.

If you’re planning to stay there, and the landlord is helpful, that might be a better solution to the mould and condensation. It won’t help with the temperature though!

Thank you, I'll have a look at those videos. It's all very confusing and I've found that there's lots of contradictory advice 😔

It is confusing I agree.

Online you will find oceans of contradictory advice, especially anecdotal because the technical issues are complex so what works for one property can be bad news for another.

Housing physics isn't simple, membranes, brick density, prevailing weather direction, eaves junction details, wall ties and damp bridging... And on and on...

Unfortunately, builders can be the worst people to go to for advice because the issues at play often take a long time to unfold so by the time something that looked great at installation becomes a problem the client is well past the point when they would complain, so builder can be unaware that there's a failure.

Lots of people just jump without looking though, hire someone and dive right in... A suck it and see approach.

But for successful outcomes it is best to have the risks analysed by a professional who is capable of doing the task, to see if it is even a good idea in that property and if so the specification properly designed.

Do not do it.

Filling any cavity leads to thermal and moisture bridging. There have been some advances in the technology where they use the Styrofoam balls instead of expanding foam material but I still would not go near it in a million years.

My uncle had it done and now has damp on his outside walls and coming down through his chimney wall.

If the external walls are suitable go for an external wall insulation, typically called overcladding. My house has this and has benefited enormously.

I have 18 years experience in the construction industry as a QS and there's no amount of discount or government schemes that would entice me to use cavity insulation.

It's actually quite scandalous the government are not banning this. Just Google the spray foam loft insulation to see countless examples of people left with unmortgageable properties after doing g work recommended by green grants and so on.

Do not do it.

The house may not even have a cavity. Can you post a picture of the external end wall? Close enough to see the bricks and mortar, not the whole of the end wall.

Is the outside rendered/ painted? It might have the wrong stuff on, we had this and house was better once we removed it and the bricks could breathe and dry out.

We have 1920s house but solid walls in the original. It is a cold house, we've improved it with 2ft of loft insulation and lots of filling weird holes, redoing windows, super thick curtains but it is limited. Our house also drops to about 14c overnight, some room get to 8c!

The styrene balls were OK for my neighbour.
The stuff that was put in my walls via a government grant caused damp. CIGA paid for it to be removed but refused to pay for the damage caused inside my home. It cost me thousands and the side wall of the house is still not right but no one can find out why.
I wouldn't touch it, especially in an area of higher rainfall.

I’m amazed the house can’t get any warmer. I have an old semi detached house with no cavity wall. If I have my thermostat at 19 I have mould, if I have it at 20 i don’t have mould. I can get my house to 20.

If your house won’t get that warm even though it’s older I’d be wondering if your boiler is too small/faulty or if there aren’t enough radiators, do they need bleeding, are the radiators big enough for the rooms?

you need to heat and ventilate to combat mould.

No not rendered, does have some paint on the front of the house but issues are mainly are on the walls at the side of the house. In my opinion it needs repointing as I can literally scrape away the mortar with my finger nail in most places, so I'm positive that it's soaking water up. I've complained to landlord about it and they did send out their "handyman" who just did small sections, i had him back out twice after to do the rest but he didn't, muttered something about needing scaffolding but he could have atleast finished the lower half of the house 🙄

Windows could also need replacing, we get ALOT of condensation which i have to use the window vac regularl. They're double glazing but not very thick, neighbours house has thicker windows and doesn't have condensation like we do. Air house out regularly too, makes little difference. We do have loft insulation, but its a mess up there, so no idea if it's standard measurements or whatever there's piles of it in some areas 🤷‍♀️

No, no previous mould issues. Was definitely caused by the wall insulation - house had no airbricks and inadequate loft ventilation though, if the other ventilation had been better it might not have been as big an issue. I’d recommend you check out the other ventilation of the house.

I know, it's really strange. We have really high ceilings so that could be a problem? The radiators feel red hot to touch but don't give out much heat into the rooms, I have put those foil things behind the radiators too, they made a small difference.
the only rooms that get warm when the heating is on is the dining room and daughters bedroom, neither have mould or damp issues. Daughters room does have the boiler in and the dining room is directly below. Both are on the outside walls too, so unsure why these rooms are okay 🤷‍♀️

This house doesn't have air bricks, it is something I noticed before as previous home did. I'm not sure about loft ventilation but there's loft insulation in there that looks like it's just been randomly chucked down and thrown into various piles, so it could be possible that there's not much ventilation going on in there 🤔

I can post a photo when I'm home.

The other thing could be penetrating rain causing the brickwork to be damp. Our back wall needs repointing and that is causing a few issues in our bedroom.

it’s odd that the radiators are hot but the room not getting warm. Could be crap windows, the radiator not the right size for the room, not enough loft insulation

There were or are a lot of cowboys doing cavity insulation and a lot of people having to try and get it removed. If it's not done properly it can bridge the cavity and cause damp. I wouldn't do it, too much potential for problems and very expensive to try to remove if something does go wrong.

If you have damp already you need to establish whether it's from the inside (condensation) or the outside faulty damp proof course (rising damp), leaking gutters or downpipes, etc. Get a damp survey done before you do anything else.

Damp bricks conduct heat really well, dry walls conduct heat fairly well, but as in wetness and that great loss will increase a lot... So if your walls are wet they will lose a lot of heat for you.