Cavity wall insulation vs insulating plasterboard

[spoonbed]

We have one room in particular in our 1940’s built house that is very cold. Have had an insulation company out today to survey, and a camera revealed that the cavity has no insulation whatsoever, just air. We discussed getting the external walls of this room injected with cavity wall insulation, and also the option of fitting battens and insulated plasterboard to the inside.
The plasterboard option is around 3x the price, so ideally I’d like to go with the cheaper option, but only if it works!
Any thoughts please?

 

[^woody^]

One is not better than the other.

Internal insulation involves much more work along with a higher material price.

However you'll need to know the actual product and material type before you can compare efficiency.

Factor in greater disruption during the work and reduced room size afterwards.

 

[spoonbed]

Thanks for the reply. I guess the question is if the internal works are going to be worth the extra expense and disruption compared to CWI?

 

[mrrusty]

Don't fill the cavity! It will most likely be vented (are there airbricks just in to the cavity that don't go through in to the house?) These help to dry the cavity if/as/when water penetrates the outer brick skin (as it is designed to do - why we fit cavity trays, weep points, drip points on cavity ties etc.).

A ventilated cavity will help to keep your house dry. If the house was designed to have this, I would think very carefully about filling it.

If you can internally insulate using either insulation backed PB or separate battens, insulation and PB then go for it. A much better solution that maintains the cavity.

 

[veedee]

I would not insulate the cavity. Too many horror stories.

Personally, I would go for IWI. I recently installed this (albeit on a solid wall) and I am very happy with the outcome.

The only downsides are the slightly reduced room size. Fixing to dot and dab wall can be annoying and IWI costs more.

 

[robinbanks]

why we fit cavity trays, weep points, drip points on cavity ties etc

In the 1940s?

Too many horror stories

Millions of homes have CWI (gov estimates 9 million). The horror stories, which are the only things you'll ever read because good news isn't reported, come from a tiny small percentage of those. It should also be borne in mind that the stories are just that - hearsay, effectively, unless there is a repository of properly analysed installs that went wrong for a specific reason and the CWI was permanently removed again?

Fully filling a cavity wall is an accepted method of insulation that is even practiced on new builds today

and a camera revealed that the cavity has no insulation whatsoever, just air

but all the other rooms in the house, which are warm, do have CWI?

 

[spoonbed]

In the 1940s?


Millions of homes have CWI (gov estimates 9 million). The horror stories, which are the only things you'll ever read because good news isn't reported, come from a very small percentage of those

Fully filling a cavity wall is an accepted method of insultation that is even practiced on new builds

but all the other rooms in the house, which are warm, do have CWI?

There’s a mixture of rooms where we have managed to insulate during refurb, and rooms where cwi has been installed (by previous owners).
The main cold issue is just in this one room, and it also has a couple of damp spots also

 

[mrrusty]

In the 1940s?

My 1902 with 2" cavities definitely has (lead) cavity trays

It also has IWI with no issues (whereas our good friends with a 1930's with CWI have damp issues after having it done......)

Fully filling a cavity wall is an accepted method of insultation that is even practiced on new builds

It's so successful that there is a huge industry that has sprung up taking it out - do a quick google for "remove cavity wall insulation". If it was so good, this wouldn't exist......

 

[jeds]

There's nothing wrong with cavity insulation, done properly. My question would be if your cavities are suitable, which is highly unlikely in a 1940s house? Also, even if your cavity was suitable, the benefit of CWI provided by a small cavity is negligible in modern terms. Might have been OK 20 years ago, but not today.

My advice is internal wall insulation.

 

[^woody^]

Thanks for the reply. I guess the question is if the internal works are going to be worth the extra expense and disruption compared to CWI?

The question should be what product are they insulating with. If you are going for the internal disruption then you may as well ensure that the product is the most efficient type and of the greatest thickness that cost and practicalities allow.

Again you need to know the products and the installer should be able to work out a payback period over 15 years or so - ie how much you will save compared to how much it costs.

Then you (and only you) will know if it's worth the disruption and cost.

 

[noseall]

A ventilated cavity will help to keep your house dry.

And cold.

 

[mrrusty]

And cold.

not with internal wall insulation wot we have.

 

[davidm1969]

"The main cold issue is just in this one room, and it also has a couple of damp spots also"

I was looking into this myself [cavity wall vs IWI] and in at least a couple of places it reminded me that damp insulation is no insulation....so sort out the cause of your damp spots first..... if insulation in the cavity gets wet, or the insulation in the IWI does, you will have caused yourself an expensive headache, and no warmer a room, by all accounts.

For cavity wall insulation there are some options see https://www.cse.org.uk/advice/cavity-wall-insulation/ which also gives info on guarantees - if I was choosing this I was thinking of beads rather than expanding foam, and using one of the companies that removes as well as installs it....as they will know what goes wrong and will maybe be less likely to do a dodgy install.

IWI will be cheaper if you can just attach insulation boards-depends on the walls [see https://energysavingtrust.org.uk/si...s/Solid wall - internal wall insulation_0.pdf ]

For both options get at least 3 quotes


Good luck