wall insulation in new extension

[ssharrow]

Dear All, we are doing a ground floor extension on the house (side and rear) next year. I wanted to ask what the norm is when insulating cavity wall (brick outside and block inside). The cavity is 100mm - is it normal to fill the cavity completely with insulation? architect is specifying full fill cavity 100mm dritherm 32. I have read (online, books, etc.) that it might be better to have 50mm insulation for example and leave a gap in the cavity in case water were to penetrate the outerleaf of the cavity wall. I just want to make sure that the specs are all in line with what the normal approach to doing a standard home extension is. Many thanks in advance for any replies and advice.

 

[stuart45]

You can use full fill if you like. The batts are designed with the fibres going one way to stop moisture penetration. Some builders prefer part fill, so it's a matter of personel choice.

 

[freddiemercurystwin]

Nowt wrong with your architects spec. As mentioned you can do either provided the right insulation for each scenario is specified, which has in your case.

 

[ssharrow]

Aah OK, many thanks for your reply. When a builder does go part fill, I guess they still need to ensure that the insulation effectiveness is still the same as a 100mm batt right? Is the insulation something that I can rely on bulding control to check (to make sure builder is using correct spec of part fill insulation)? Thanks

 

[stuart45]

Check it yourself. Part fill will be insulation boards. Building Control can miss stuff. You might not see the BCO too often.

 

[ssharrow]

thanks, so what u value or specification is required to be compliant with today's building standards? (so I can check whether the insulation being used is not inferior to the insulation provided by a 100mm batt. Many thanks

 

[tony1851]

A 50mm board, such as Kingspan or Celotex will be roughly equivalent to the fullfill batts in terms of insulation performance.
Personally I would use full-fill; as Stuart has advised, they are designed to repel water.
Rigid boards have to be carefully fitted to be effective and they are less forgiving of indifferent workmanship.

 

[ssharrow]

Thanks All for your input, we'll use full fill then - seems like the standard thing to do.