best options for cavity wall insulation?

I am just about to build a new house and it is with interest I read all the various options, like an earlier post I am lost as to the best foot forward. I was planning to go with Xatherm or Kingspan 60mm cavity with the joints taped and have a 62mm internal/external wall, so I was quite happy until i was then told all of these options....

150mm bead filled cavity
150mm cavity 60mm hard and the remainder bead filled.

I seem to agree with ONQ that for years we have talked about this cavity and stopping damp and thermal bridging and now it is all ok. i find it impossible to great real advice as most BER assessors ( I stress most and not all) only got into this game a few years ago and have some basic knowledge but no more. My real question is despite all the posts here I am still confused as to what is the best option I want to achieve as high a rating as is practicable...
 
The point made by Birds is an interesting one, and I would like to provide some historical context to the situation which we now find ourselves in.
Before WW2 in the UK, the function of an external wall was twofold, these being:
1. to provide structural support and
2. to offer resistance to moisture penetration.
Such walls were generally constructed in solid concrete or masonry, and were typically quite think. Their thickness was dictated mainly by the depth required to avoid moisture penetration through the wall to the interior of the dwelling.
During the rebuilding effort which was required after the war, a drive to reduce the amount of material required in the walls of dwellings led to the development of the cavity wall, with the cavity taking the place of material in the role of stopping moisture ingress. These early cavities were quite narrow (40-50mm being typical) but fulfilled their stated role.
In the late 1940s and early 50s, the introduction of insulation in external walls was phased-in in order to reduce the costs of heating for working class families. The obvious location for the insulation at this stage was in the cavity, where it would be protected from both the weather and from the occupants’ use of the house internally.
The oil crises in the 1970s resulted in further insulation being incorporated into the cavity, thus resulting in ever widening cavities.
With current and proposed levels of insulation getting ever higher (with ‘passive’ and ‘carbon neutral’ standards around the corner), the width of cavity currently which will be required in the near future (150-225mm) is in my opinion becoming impracticable.
 
Looks like someone's been on the RIAI Conservation Course threebedsemi - most impressive :)

Birds,

Its sounds like you've been talking to a beads salesman.
One way to have your cake and eat it is to externally insulate.

One concern will be security and structural sound deadening as well as the cold bridges at threshold/ground floor and at eaves.
Structurally the house might be built using; -

  • 225mm solids and hollow blocks with
  • precast or cast in situ floors if required
  • resting on a ring beam

- all to your structural engineers sepification.

External insulation, with open cill and threshold details from an approved supplier can be considered.
All of this method needs careful detailing, but it seems to be gaining popularity, even if it does seems to rest on the render for its water tightness.

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
 
Onq
haven't done the course, but I do seem to have more time on my hands to read lately for some reason...

In relation to your suggestion, I have recently used exactly this wall build up on a dwelling house, and I was very impressed with it. It deals with cold bridges at most junctions a good deal better than traditional cavity wall construction, allows you basically unlimited depth of insulation, and has in my opinion a clear advantage that all the insulation is in the same location. I have some concerns about the 'cavity insulation and drylining' systems currently being used, as they can have surprising results with regard to interstitial condensation within the structure.

Any external insulation system should have at least BBA certification (British Board of Agrement) if not the more expensive Irish Agrement certification, and that the fitter be approved and trained by the system supplier. Ideally meet with both the fitter and the technical advice guy from the suppliers company on site at the start of the project.

My only other reservation would be that you wouldn't want your aspiring Henry Shefflin practicing penalties up against the wall.
 
Onq, yeah a beads man as well as kingspan, builders, geothermal: everyone has a different view point, finally decided that i am going with 150mm blown cavity and then as the house is a dormer I am going to use the spray insulation for the upstairs as I can get the best result for airtightness with this method. Have investigated using other methods to and this appears to be the easiest and most straight forward.

Has anyone done this up stairs???
 
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