Cavity wall advice please help

[Downcast]

Is 100mm loft roll ok to use as insulation in a 100mm masonry cavity wall? It’s a small extension on back of garage 5mx3m single storey.
My builder says it’s fine to use and no need for the more expensive slab insulation which you are supposed to use as you build up walls.
Any advice would be appreciated

 

[stuart45]

No, it's not the correct insulation to use in a wall. It can allow moisture through.

 

[Downcast]

Hi I didn’t think he was correct he is old school, and says this has been used for years previously. I am going to get him to remove it and then I will have to get an insulation contractor for wool or bead blown in type not sure which is best?

 

[stuart45]

Has the Building inspector seen it?

 

[^woody^]

old school

I think he played truant a lot.

 

[JP_]

and then I will have to get an insulation contractor for wool or bead blown

the problem with that is that all the cost is on you - I guess it will waste a lot of money.
Surely, the builder should just build to current standards using the correct materials.
Using loft insulation in a wall - doesn't take a genius to realise that this might not be the best idea. Besides, surely it was much harder for the builder to do this? How did he roll it out on a wall and keep it in place?

 

[Downcast]

No, our plans stated we would use rock wool 100mm insulation, however the builder decided to get earthwool loft roll as he said his building merchant said this is perfectly fine to use in such a small extension.
BC are coming to check after roof is constructed. I have asked him to remove it and will instead go for the only option now of blown in insulation, but not sure what is best?

 

[Downcast]

The wall ties I think kept it relatively upright. We cannot put in the slabs as wall are built up to 2.6m high and ties don’t look exactly uniForm in order to slide them in. I know it’s a disaster but thinking rather get this stuff out than have problems in future

 

[dontbelieveawordofit]

polystyrene beads are the least trouble.
who puts wool in a wall?

 

[Downcast]

I thought mineral wool or rock wool could be blown in as well as poly beads?

 

[AS-Kent]

polystyrene beads are the least trouble.

Agreed - easy to order and put in yourself, no need for a specialist if you can still see the top of the cavity. I did this for an elderly neighbour when I discovered their 'Pro' installed insulation beads (many years ago) were about 2-3ft short of the top of the bungalow cavity. Just cut the bags and pour it in...or you could probably rig something up to blow them in. Can't vouch for this insulation being as good as the proper built-in stuff of course.

 

[^woody^]

Arhh yes, but does blown fibre (or beads) achieve the required 0.18 W/m²K performance?

You will need additional insulation on the inner face.

 

[frutbunn]

Hi I didn’t think he was correct he is old school, and says this has been used for years previously. I am going to get him to remove it and then I will have to get an insulation contractor for wool or bead blown in type not sure which is best?

Well I've got to say I have only seen it used once since insulation became more common following the first amendment in '82ish of the B Regs 1976. I made him take the wall down and rebuild with the correct insulation. I very much doubt he's been using it for years, no BCO would allow it, he's talking complete crap. Just out of curiosity where does he tie up his horse when he arrives on a morning?

 

[JP_]

does sound like he thought he'd try to save some money, thinking you would not notice and question it.
Get the building inspector out, if they reject it then he will have to rebuild it properly. Sounds like the alternative is have a smaller room?

 

[Celeronmanuk]

I made our bricklayers take a wall down when they left out the insulation as they'd run out. They tried to argue it was better without insulation. Sacked the builder shortly afterwards.