Cavity wall insulation question.

We moved into our 1970's built bungalow about 18 months ago.
As a result of a kitchen /diner extension build I was wondering ....

The structure of the bungalow is ..
Outer brick skin
40mm air gap
Building paper
12mm Ply
4” stud walls with polystyrene infills
Foil membrane
Plaster board and plaster.

Would it make sense to have the 40mm air gap filled with an injected insulation material i.e. loose fill/foam ? I know that this is a narrow gap but I believe that there are modern infills that can now be used in such spaces.
What about damp bridging the gap ? There are endless horror stories about this so how can it be prevented
OR
should I just leave things as they are ?

Part of the reason for asking is that our heat source for C/H is an air to water heat pump and every thing I read about this is that insulation is the key.
If it is a good idea to insulate the cavity (first time we will have ever done anything like this) then what do I need to look for when googling local installers and any tips/advice ?

Many thanks
Brian.

Brian Lacey said:

our heat source for C/H is an air to water heat

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I didn't think they were suitable for properties of that age. How many kw is it? Impressed if it's coping... I might consider one myself.

garyo said:

I didn't think they were suitable for properties of that age. How many kw is it? Impressed if it's coping... I might consider one myself.

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It was already installed when we bought the place. Unit is about 6 yrs old (Altherma LT), feeds 11 rads and 2 towel rails, Works perfectly OK. No idea what KH it is.
Cheers
Brian.

I would say definitely not, you would effectively be changing the wall construction which could lead to condensation risk. A pain in an all masonry cavity wall, but disastrous in a combined brick and timber frame construction.

I would suggest 50mm celetex on the coldest external walls, 50 x 25mm battens laid flat over then plasterboard. Or insulated plasterboard. I know its a pain, meaning radiators, skirting etc being moved but the safest solution. Thats assuming your walls need improving more than other areas like loft, draughts etc.

Many thanks for the advice. All noted.
Cheers
Brian.

A timber frame needs a ventilated air cavity.

Thank You, will not do it !
Cheers
Brian.

Brian Lacey said:

No idea what KH it is.

Brian.

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There is a data tag on the outdoor unit that shows it's KWs.

No tag that I could see but original paperwork from 2009 installation says 11.2KW. I assume it's the same.