Sagging cavity wall insulation: what to do?

[abernabei]

Hi everyone.

 

we're in the middle of refurbishing a mid-60s ex-council maisonette.

 

The property has insulated cavity wall, with a cotton-like material which I guess is mineral wool.

 

We bought K118 insulated plasterboard (50mm phenolic board + 12.5mm plasterboard) to increase insulation and also to hide radiator pipes.

 

However, after removing the window sills we have realised the cavity insulation has sagged in at least one of the walls (it hasn't in other likely-less-exposed-to-rain walls), leaving most of the first floor wall uninsulated.

 

My first thought was to call someone in to top the cavity insulation up and resume our plan.

However, after doing a bit of research it turns out there are a few schools of thought out there:

- those who think cavity wall insulation without external wall insulation causes damp and should be removed, not topped up

- those who think you should remove the old insulation and install new one

 

Do you have any advice?

 

What should we do?

 

I have attached a pic of the view from one of the window sills on first floor, and another one of the section of the wall next to the window, which shows that section of the wall is now uninsulated.

Edited October 30, 2023 by abernabei

[markc]

The dreaded ‘sponge’ insulation so many got suckered into. Get it removed and replaced.

[abernabei]

thanks Mark. What kind of insulation should I aim for?

[markc]

2 minutes ago, abernabei said:

thanks Mark. What kind of insulation should I aim for?

I would go for blown bead eps, interesting to see what others would opt for

[abernabei]

thanks, will keep that in mind.

It will be interesting to see how they can remove and replace insulation without affecting the neighbouring (adjacent) flats above and next to us.

I am not sure there's any separation in the cavities between the flats.

[nod]

You will find it very difficult and expensive to remove You May find your only practical option is to top up 

[Andehh]

Have you ever experienced internal damp? any evidence of it anywhere?

 

If the answer to both is 'no' (especially over such a long time period) then top up and move on!

[abernabei]

We haven't moved into the property yet so it's difficult to say.

 

After we removed the wallpaper a few of the first floor walls (i.e. those which are not insulated) were partially covered in black mould. Not all of the uninsulated ones though.

 

The wall that had the most was next to the bathroom (not sharing wall surface with the bathroom, but next to it along the same side), and there was evidence of a previous bathroom leak, which I guess must have caused that.

 

That first floor wall is actually still insulated, we believe.

The first floor walls which are definitely not insulated (anymore) did not have signs of black mould, but it is also true that they were originally not covered in wallpaper, so it's hard to know whether that black mould was a consequence of the insulation, or the bathroom leak, or the wallpaper plus the wardrobes standing in front of it, or all of that together.

 

There was only little mould growth on the exterior walls on ground floor, which are the walls where the insulation has now squeezed into, except in the kitchen area...there's so much black mould behind the kitchen units it's unbelievable.

 

In other words, it's difficult to say whether the insulation is/was causing damp

 

56 minutes ago, nod said:

You will find it very difficult and expensive to remove You May find your only practical option is to top up 

why is that, out of interest?

 

Can they not remove it with some kind of hoover through external holes and from the currently exposed window sills?

They have easy access to the cavity.

Edited October 31, 2023 by abernabei

[markc]

Damp further up is probably condensation related, damp at the bottom often needs the wet soggy insulation removing. Took a couple of us a day to clear out a 3 bed semi, 6 or 7 places we took out 4 bricks to allow access for a vacuum hose and also removed internal window sills etc to get in that way. The stuff we removed was horrible (luckily we hired an industrial vac) wet and it stunk

[abernabei]

ouch.

I wonder how they can remove and install new one without affecting neighbouring flats, which are likely part of the same cavity and will not want to do the same works (they are renting).

[markc]

22 minutes ago, abernabei said:

ouch.

I wonder how they can remove and install new one without affecting neighbouring flats, which are likely part of the same cavity and will not want to do the same works (they are renting).

The adjoining cavity would just benefit from you blowing beads in to fill their voids, you can’t separate so they just blow more beads in to fill any voids, not ideal but needs must.

[Gone West]

4 hours ago, abernabei said:

ouch.

I wonder how they can remove and install new one without affecting neighbouring flats, which are likely part of the same cavity and will not want to do the same works (they are renting).

A cavity brush is usually used to keep the insulation your side.

 

https://speedybrush.com/cavity-insulation/

 

 

[abernabei]

thanks everyone. We have verified the concrete slabs in the ceiling separate the insulation of each floor, so at least vertically we are separated from the neighbours.

Horizontal separation TBC.

 

We got a quote from a company to remove current insulation and blow new mineral wool for 3500£ under CIGA.

They say mineral wool is still their preference over EPS beads.

 

The product is Provincial Seals CWI18 White Wool insulation.

 

 

[IGP]

EPS beads every time over blown in wool. 

[abernabei]

The company that is proposing mineral wool handed over a BBA certificate for its wool products and said they considered EPS beads but found mineral wool to be superior when it comes to failure rates.

They said the reason why other installers use EPS beads is it takes half the time to install so they can do more jobs in the same amount of time.

Edited November 4, 2023 by abernabei

[IGP]

I’ve no doubt about the BBA certification for their wool installation. The problem I see with all blown wool insulation is that the wool will snag on the rough surface inside the cavity and wall ties with mortar snots and create voids on the lea side from where it is blown. This could create cold spots leading to all sorts of problems. 
 

Blown EPS beads on the other hand don’t do this and also don’t have capillary action to retain water, unlike wool and therefore can never get soaked themselves. 
 

Cavity batts for full-fill during construction however I can see could be superior to EPS for u-values, but that’s a different question. 

[RobLe]

Our home was built in 1963, brick outer block work inner with a cavity.  Went with glass wool instead of eps due to mains cable wiring found routed in the cavity.  Eps may slowly leach out the plasticiser in pvc cables leaving them brittle - it’s why cables come wrapped in plastic if they are near polystyrene packaging.

This was 20 years ago; now we’ve got EWI as well, which is excellent!  When the house was being EWI’d I found (and fixed) CWI was missing in a few places - under windowsills, tops of cavities, behind upvc cladding (there’s still a cavity wall behind there).