# Cavity Wall Insulation - how to deal with a botched job



## ronnie (5 Jun 2009)

I'm having a two storey extension done to my house. The builder installed Kingspan board in the new cavity walls. I assumed it was being done correctly but I discovered that large lumps of masonery were left inside the cavity and therefore the insulation board is not sitting flat against the inner wall. In some places there are quite big gaps. In addition, the boards are not fitted together properly in places, and the wall ties are not put in properly in places. The result being that some of the boards are loose. In other places there are no wall ties at all, eg under the window openings, and I have been able to lift out the kingspan boards. There are no doors/windows in the extension yet, which is how I can see into the cavity in some places. The insulation is a total waste of money as it is not installed correctly and is therefore useless. I'm wondering is there anything that can be done to salvage the situation, before the walls are sealed up. I don't want to dry line the walls internally and lose the thermal mass effect of the walls.


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## Towger (5 Jun 2009)

In my non expert opinion this is (all too often) the normal standard of quality used to install this type of insulation, which of course renders it mainly useless.  
Would it be possible to inject (from the bottom of the wall) a closed cell foam into the cavity?


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## aulita (12 Jun 2009)

Towger said:


> In my non expert opinion this is (all too often) the
> Would it be possible to inject (from the bottom of the wall) a closed cell foam into the cavity?


 
No problem! Will have your own mushrooms as well


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## david ross (16 Jun 2009)

ronnie said:


> I'm having a two storey extension done to my house. The builder installed Kingspan board in the new cavity wall insulation. I assumed it was being done correctly but I discovered that large lumps of masonery were left inside the cavity and therefore the insulation board is not sitting flat against the inner wall. In some places there are quite big gaps. In addition, the boards are not fitted together properly in places, and the wall ties are not put in properly in places. The result being that some of the boards are loose. In other places there are no wall ties at all, eg under the window openings, and I have been able to lift out the kingspan boards. There are no doors/windows in the extension yet, which is how I can see into the cavity in some places. The insulation is a total waste of money as it is not installed correctly and is therefore useless. I'm wondering is there anything that can be done to salvage the situation, before the walls are sealed up. I don't want to dry line the walls internally and lose the thermal mass effect of the walls.


*Installing cavity wall insulation*

                      To install cavity wall insulation, your property must have two masonry brick or block walls, with minimum 50mm of space between them. Homes built between 1930 and 1995 are the most commonly requiring cavity wall insulation. If your home was built before this period, the property probably has solid walls. If it was built later, insulation is most likely included within the walls.
                      Many Irish dwellings have cavity walls that could be filled. You can find out if you too have cavity walls by measuring your walls at a door or window for thickness. If the walls are solid, the measurement will be around 23 cm thick, while if a cavity exists, the wall will be around 30 cm thick. You can also contact the SEI  local installer to survey your property in this regard.


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## Eng Car 1 (16 Jun 2009)

Ronnie, Are you supervising the work yourself or is there an Architect or Engineer overseeing construction. I would be worried about your comment that the wall ties are incorrectly located/secured and the structural stability given that its a two storey dwelling. I would advise that if you do not already have an architect or engineer on board you should at least get a Strucural Engineer out to advise you before allowing the builder to continue further.


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## Sconhome (16 Jun 2009)

ronnie said:


> I'm wondering is there anything that can be done to salvage the situation, before the walls are sealed up. I don't want to dry line the walls internally and lose the thermal mass effect of the walls.



Fire your builder and anyone on your design team that has allowed this pathetic situation to occur.

You are going to have a lot of difficulty making something decent out of this mess. The Kingspan should be a complete plane with the cavity fill capable of filling the remaining 45-50mm as a complete unit.

To minimise thermal bridging your insulation should have no breaks or gaps. Partial cavity fill may work at a reduced efficiency. My advice would be to consider external insulation as a sure means of achieving the required thermal rating.

Remind your 'builder' that building regulations are supposed to be complied with, probably best to show him a copy.


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## ronnie (18 Jun 2009)

A structural engineer did the plans and he is supervising the job at certain points but he obviously didn't supervise the installation of the cavity insulation.  I happened to spot the situation because I did a one day course in sustainable energy ireland, on insulation and then went back and checked what the builders had done in my extension.  I have now asked the engineer to have a look but what can he do now.  The walls are up and the roof is on.  Short of knocking the whole thing down and starting again - which I would do if the builder will foot the bill - I can't see what can be done. I'll  wait and see what the engineer says.  I have stopped the work in the meantime. thanks Ronnie


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## ronnie (18 Jun 2009)

Thanks for this advice.  I will consider external insulation.


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## onq (18 Jun 2009)

ronnie said:


> A structural engineer did the plans and he is supervising the job at certain points but he obviously didn't supervise the installation of the cavity insulation.
> <snip>



Its not the engineers job to do that.

This is a simple task to do when done properly, but snots of mortar in the cavity are more usual than large lumps of masonry. There should be two "clean" faces facing each other with the insulation tight to the inner leaf.

Tell the builder you're refusing to pay him until this is sorted. He may suggest a "full fill" type of in-cavity insulation - there are a few around now and some have agrément certificates. This could sort out your problem.

However...

Even in-cavity solutions may leave cold bridges at heads [top], jambs [sides], cills of window opes and thresholds of doors [bottom] if more advanced details aren't used to create thermal breaks.

For example if the inner leaf return to the outer leaf is held back 25-50mm then insulation can be placed at the jambs between the inner leaf return and the outer leaf, placed against a vertical DPC placed against the outer leaf itself. Such details need additional wall ties.

You should also check there is insulation under the floor slab and that he has installed a Radon Gas Barrier and Collecor Box [sounds like the structural bay may be large enough to need it].

FWIW

M.


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