# cavity wall insulation



## seantheman (6 Sep 2009)

I live in a dormer bungalow built 2000. it has 100mm cavity with 60mm aeroboard cavity board. was thinking about filling the cavity with blown rockwool/fibre.Anyone on here done something similar? Any advise pro or con this idea welcomed, especially peoples own experiences.


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## onq (6 Sep 2009)

I have little direct experience of these products.
The one installation I have seen was a form of pellet, not fibres at all.
Problems are the usual when filling a space you cannot see into:

Is the existing insulation sitting flush against the outer face of the inner leaf.
How do you ensure full fill occurs at opes - under sills, over heads. at thresholds.
If the fill goes below DPC, what stops the damp rising.
How do you fill to the top of the cavity?
How do you prevent a cold bridge at the top of the cavity if there's a brick closer.

See? All the usual little problems 

Only use Cavity Fill insulation if it is has an Agrément Certificate.
Ask to see buildings insulated using the product.
Ask to check and see the product installed
Install it strictly per the terms of the Certificate.
Strongly advise to use a registered installer and get a guarantee.
Check what the guarantee excludes.

ONQ.


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## Peter C (7 Sep 2009)

We were in a similar situation, decided against rockwool heard it has problem slumping into the cavity, went with beads checked agrement cert and installers other jobs, have to say we are very happy with the result, one north facing room was difficult to heat now its much better.


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## seantheman (7 Sep 2009)

Thanks for the input guy's. onq the reservations you have are exactly in line with my own, which is why i was looking for feedback from people who have had this carried out.Correct me if i'm wrong but i thought that with aeroboard cavity insulation that the board went tight to the inner leaf with toggle on wall tie. This, if tight should leave 40mm gap between aeroboard and outer leaf, which is the area i'd like to have filled.Peter it's reassuaring to know that you are benefitting from this procedure


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## Charlie 07 (8 Sep 2009)

looking at doing the same-beads/foam/fibres?!?
would also like to know how people got on? Good/bad stories!!!!


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## onq (10 Sep 2009)

seantheman said:


> Correct me if i'm wrong but i thought that with aeroboard cavity insulation that the board went tight to the inner leaf with toggle on wall tie. This, if tight should leave 40mm gap between aeroboard and outer leaf, which is the area i'd like to have filled.



The "toggle" I think you are referring to may serve two functions.

#1. The earliest designs of cavity wall ties, either twist or butterfly, has a point in the middle to allow water to drip from in order to prevent migration of moisture from the wet outer leaf to the dry inner leaf.
"Snots" of mortar landing on the wall tie often caused spots of damp on otherwise perfect niner leaves.

#2. As the depth of insulation became deeper, going from 40mm to 60mm, the toggles started appearing, and to me some of the designs seemed to sacrifice their "drip" function for use as a restraint to keep teh cavity insulation pressed against the inner leaf.

In relation to the volume you hope to insualte, bear this in mind:
You need to check whether this combined insulation will cause problems.
The cavity fill insulation may be designed to work alone and bond to form a mass in the cavity that prevents teh passage of moisture.

Its important to understand how this works and back to the agrément certificate you go 



If in doubt, contact the manufacturer and ask him for a list of buildings using his product.
Visit the buildings and ask the users thereof how the product holds up in use.
Ask them if there are any dark patches on walls suggesting mould at cold bridges where the cavity isn't filled properly.
Ask them if there aer any damp patches on the plaster or any unusual smells, suggesting water may be migrating across.

There is no easy way to do this, BTW.
You need to do research specific to the product you hope to use.
Do not accept comments at face value which may be about generic but not exactly similar products.
You'd be surprised how much time can go into product research on a new build or refurbishment if you're using new products.

HTH

ONQ.


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## Peter C (11 Sep 2009)

Many moons ago brother in law had his house done, at the time they were using loose polystyrene beads which were a major headache when he was getting the windows replaced as the beads flowed out, today that system would not be used. I reckon a lot of research has been carried out since the first products were used and a lot of the earlier mistakes corrected. 20 years later and the brother in law still reckons he got great value.


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