Cavity wall insulation

[Benzowner]

Not all cavity insulation is bad. You can install DriTherm mass filled in a new build and it does a fab job because it is non absorbent. Used properly it wouldn’t cause any issues whatsoever.

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Dritherm many moons ago was a Pilkington fibreglass product, how times have changed I guess Knauf took over from Pilkington. Used to be 50mm thick when I sold insulation, but even back then they sold a partial fill cavity system.

Its a good product because the fibres run longitudinally so preventing moisture from bridging the cavity, when full fill cavity is pumped in, they have no control over whether a moisture bridge is formed or not.

 

[PXW]

Thank all for your comments - really helpful. I've been doing a fair amount of research as you have given thoughts and feedback, and I think I have come to the following:

1. It looks as though it is the Urea Formaldehyde product. I'm not worried about fumes etc - reports I have found suggest that the fumes issue is very temporary; we've been in the house for 10 years and best guess is that the stuff has probably been in there for at least 25-30 years before that.
2. The sample I managed to extract seems OK - it's not robust, but nor has it crumbled to dust. I wouldn't have installed it, but where it is not causing a problem, I'm disinclined to spend a lot of money having it all extracted. I did wet a sample, and once it dried out it was pretty much as it was at the start.
3. Where there is damp coming through we may need to do more. There's a possible dpc bridge at that place, so the plan of action is to deal with that (which requires rebuilding an external staircase) and then see whether it dries out sufficiently. If it doesn't, then I'd look to do a more localised removal.
4. I did consider Ant's gold standard solution of removing it all, then externally insulating and then rendering on top. I did a quick on-line search on that, and I would be looking at something approaching £40k for our house. Mrs PXW gave me one of "those looks"....you guys will know what I mean!

Thanks again all - I feel a lot more comfortable that I know what I'm doing now!

 

[Petrol Pete]

OP , have you tried setting light to the sample you have ? Just for research purposes natch'

 

[PXW]

OP , have you tried setting light to the sample you have ? Just for research purposes natch'

Hadn't occurred to me...but I just tried it! Very disappointing - it didn't burn independently, but readily turned into a tiny quantity of black ash when held in the flame....

(I'm sure someone with a scientific background will tell me that is self contradictory, but that's what I observed )

 

[m80]

OP , have you tried setting light to the sample you have ? Just for research purposes natch'

That seems like an extreme method to get rid of what's in the cavity.

 

[m80]

I did wet a sample, and once it dried out

Did it hold water?

I've seen so much debris at the bottom of a cavity when I chose to replace sodden bricks with engineering bricks (longish story but a labourer blew the backs out of a whole house drilling for injection and didn't tell me till he'd finished drilling the backs out of the lot).

Removal of that lot was beneficial.

 

[PXW]

Did it hold water?

Yes, in a spongy sort of way. Dried out in a few hours though, and didn't degrade or fall apart.

 

[mioba]

5cm thick foam boards surface layered with foil is what they use nowadays

 

[Deleted member 113659]

……and I would be looking at something approaching £40k for our house.

I didn’t charge anything like that.

Shame I don’t live nearby as I’d be happy to help out.

 

[Deleted member 113659]

Yes, in a spongy sort of way. Dried out in a few hours though, and didn't degrade or fall apart.

The problem is that it NEVER has chance to dry in the cavity.

 

[Athey]

You could put wall weeps in to give the moisture a way out.

 

[Piff]

One for the builders on here. I'm revisiting energy efficiency at PXW Towers. The house was built mid-late 70's and I started to wonder about any cavity wall insulation. So - I raked out a joint in the brickwork and found this stuff inside. It's white, fluffy-foamy, very delicate and very light - can anyone tell me exactly what material it is? I know that there are some cavity insulation materials that are not now considered safe/effective...and I'd like to know whether this is one of the problem ones! From some desktop research, it looks like it could cost a substantial sum to have it removed and replaced if it's a problem...

I'm partly investigating because a few places around the ground floor have suspicious possible damp areas - some are likely connected to dodgy sealing around doors/windows, but one is not near any obvious source, which made me wonder about possible collapsed insulation, which could form a damp bridge.

Any thoughts or comments very welcome!

TIA

Peter

I had that stuff installed in a previous bungalow. IIRC it was free or very low cost with a grant from energy company.
I did other works which involved exposing the cavity in a couple of locations.
The first was replacing a window & the internal cill board. Looking down the cavity there was little insulation as it had been held back by cavity wall ties.
In another area I cut in an electric meter cabinet. There was little insulation there either, it had been held back bu a couple of electric cables which were dangling in the cavity.
Both suggested that the installer hadn’t drilled enough injection holes. I tried contacting them to complain but they weren’t e interested.
In another location (a low corner on a north facing wall) we suffered with condensation & then black mould. I was fairly certain that there was no insulation at that location causing a cold spot.

 

[190]

.....To my untrained brain a small 'free breathing' space between external and internal walls has got to be better than filling it up completely.

I have that and in theory I'm sure it should be good. Brick/cavity/block with 50mm of bonded polystyrene/ dry lined plasterboard. In practice though it doesn't work because it relies on ensuring the cold air from the cavity doesn't filter through small gaps in the mortar to get behind the plaster board. I'm convinced that's what happens in my bungalow and it would be more comfortable with traditional solid plaster. I've considered a full cavity fill as an improvement but I'm concerned about damp penetration particularly as the outer wall is relatively porous reclaimed Cheshire brick and we are in a elevated position.

I had the cavity filled with that white foam insulation in my previous bunglaw and had no problems at all for 10 years but that was better quality brick and very sheltered position.

 

[mattc]

Is external wall insulation and a render cost an option for you PXW?

 

[PXW]

Is external wall insulation and a render cost an option for you PXW?

Don't think so - looking at online calculators, it's a £40k job and would never pay its way. There are also some physical complications in doing it (house is upside down and built into a hill, so has external stairs which make it difficult to clad). It would also be the only rendered house on the street which would look odd - could be done, but to work aesthetically I'd probably have to do the whole slate roof/grey windows/white render thing, which would add another easy £50k to the bill!

I am looking at trying to fix the cold bridge which seems to be causing the problem, and if necessary will do an internal tanking to a couple of walls and fix the issue that way - even if I lose a couple of inches off one or two rooms internally, it will be way more cost effective.