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 does not create water and cannot cause damp.

In rare cases, walls get wet from the outside from spilling gutters or leaking downpipes, or defective brickwork or window frames. The company quoting for CWI will look for such defects, and refuse to install until they are rectified, as they may be liable for rectification costs themselves if damp is caused by filling the cavity in a wet wall.

In UK homes, the most common cause of condensation, damp and mould is excess water delivered to the house by draping wet washing around the house or over radiators. In bathrooms it is steamy showers with inadequate extraction.

Sometimes water from a roof leak runs down a wall or chimney.

Rarely, there is an unseen water leak, perhaps behind a sink or bath, or under a floor, or a broken drain making the subfloor wet.

(In some districts, persistent or driving rain can cause walls to be wet, and CWI is not recommended. That said, I live in a coastal area and suffer stormy rain blasting against my house and running down the exposed side. CWI has not made my house damp. My brickwork and pointing are in good condition.)

It depends on the type of insulation. Spray foam will not let the walls breathe, but blown in cellulose will. I assume you are talking about not deconstructing the walls but just pumping insulation in through holes. Is that correct? Blown in cellulose would be your best bet.
However, if you have a condensation and mold problem, you need a dehumidifier regardless of what you do to the walls. Make sure your bath fan and over the range fan are adequate as well.

Are you drying clothes inside?
Lots of long showers with no fa on or no window open?
No lids on pans?

We have condensation.
I think ours os most likely high flow on the shower its at least double.

Humidity in the house doesnt go below 67 % or so. Even if use a dehumidifier etc
We do also have a hill/slope at the front and house is low down
We do have CWI but the issues have been ever since we bought the house so before having windows done and CWI .

Do you use gas hobs or fire?

We don't dry clothes by hanging in the house, we do use a heat pump tumble dryer though, but it's at the back of the house in the extension. The drawer collects quite a bit of water.

There's no extractor fan in the bathroom upstairs, we open the window when bath is being used and keep it open for a good hour or more after, we keep the bathroom door shut too so the air is going out of the window rather than into the house. There's a shower downstairs, not quite an extractor fan but does have a crappy vent in the wall above the shower, it doesn't look like it would do a great deal, so always make sure DS opens the window when he's showering, window is also inside the shower so right next to the shower head. DS does spend far too long in the shower though which I'm sure will contribute to the condensation in the house, and despite our protests he does not listen 🙄

Always cook with lids on the pans, it's a gas hob. Oven is currently broken so we use the airfryer mainly but always have window open when cooking otherwise window steams up quickly.

We have a large dehumidifier upstairs, it's in the main bedroom, collects alot of water daily. And we have a medium dehumidifier in DS bedroom and a smallish one in DD bedroom. I should invest in a dehumidifier for the back of the house/ kitchen i think as that's also where the shower room is. Other DD bedroom is fine with no issues, but she does suffer from rhinitis, so I'm considering buying a air purifier for her room instead

There's also no proper extractor fan above the cooker? Just one of those plastic vent things that doesn't seem like it would be very useful. It's in the ceiling and there is like a vent with a flap thing on the wall outside but the flap never opens so I don't think any air would actually be escaping through it

I think a powerful extractor for the shower rooms is your vital next step. Builders often fit low cost 4 inch fans with a throughput around 80 cubic metres per hour, but this is not enough for a shower room, which needs around 250. I strongly recommend one that is wired to come on with the light switch, and has a timed overrun to clear the room after use.
Example https://www.tlc-direct.co.uk/Products/SLS300CRZ.html

You can get a good 6 inch through the wall fan, or, a ducted inline fan where you can extract through the ceiling and run a duct out through the nearest wall. This is often convenient in a loft and is even quieter. They are relatively big.
Example https://www.tlc-direct.co.uk/Products/SLTD250SILENTslashT.html

I am very impressed with the low noise and high build quality of Soler & Palau "Silent" extractor fans, which have a ball-bearing motor on rubber mounts. They are also sold under the Envirovent brand name (same company). They are so quiet that they will not disturb people at night.

I have no connection or trade gain from these companies.

You definitely need a proper extractor there.

I haven't read the full thread yet but the timing is perfect as I got in touch with my HA this morning asking them to have a look at my external walls because they are so cold.
The main problem is the kitchen which has two external walls.
It's that bad that there is a draught coming through the plug sockets and under the cupboards .

The cupboards are so cold that I can ( and do ) use them to store butter cheese yoghurt milk , pate and such like.

Edited to say I dont have any damp problems.

Honestly @Moon30 this sounds like substandard housing. You should not need to run dehumidifiers in a rented property, they cost a lot to run, and the landlord should have replaced the fecking broken oven in a week.
You need to move out, or get a discount for the inconvenience of living in such a property.
And don’t forget to post that external wall photo please!

Sounds like a lot of your damp problem is from internally generated moisture which isn't being effectively extracted - makes a massive difference!
Breathing, cooking, washing, laundry... Literally litres and litres a week of generated moisture with nowhere to go.

So the free goverment energy saving funding is a scam then? 😔

We had someone round to do a survey yesterday, all went great. He said rather then doing cavity wall insulation they would place boards on the inside external walls of our home and place insulation behind, then plaster over. I thought this would be great, and it would be less likely to make the damp worse and we'd be warmer but today I've had an email to say they would need a contribution of £2,900 towards the cost of the work being carried out.

I was under the impression it would be free, as we qualified with low income, there was no mention of any additional costs.
It was our landlord that informed us of the scheme to begin with.

Why they would think we would want to pay all that out for a rented property is mind boggling.

Nevermind we'll just continue to be cold while we look for elsewhere to live 😔

@Moon30

A scam?

The government scheme, probably not.

Have you tried it?

https://www.gov.uk/green-deal-energy-saving-measures

The one that we've just had around was part of a government scheme?

I've just looked into the green deal one and it looks like it's for a loan? I'm private renting so won't be in a position to do this and i can't see the landlord paying either 😏

In rented properties the landlord is supposed to contribute to government schemes, even if the tenants qualify - because ultimately their asset is getting government investment.

We have cavity wall insulation - I think cellulose from the photos online (done before we bought). Has airbricks so presumably decent ventilation. No damp. Have just had trickle vents fitted along with increased loft and under floor insulation as part of a government scheme, and no damp during winter.

Your landlord shouldn't be expecting you to fork.out.

If somebody says "I'm part of a government subsidy scheme and you have to pay me thousands of pounds"

Go and look at the government scheme yourself,

When we had a gas cooker and hob we had loads of condensation in the kitchen because it produces water vapour to burn, we changed to electric and there is a huge difference, hardly any condensation.

Wouldn't go near cavity wall insulation again. We had to pay a fortune to have it removed from one wall where a mystery damp patch had appeared. Originally had it put in as part of government scheme. By the time we developed issues with it, the installation company had gone out of business and CIGA refused to cover the removal under the Guarantee. We paid to have it removed, wall dried up, and - surprise surprise - the room with damp patch that had always felt cold is now a normal temp when the radiators are on.