Insulating knock through cavity

Quick question,

When knocking doorways through cavity walls I.e. extensions, do you insulate the exposed cavity? There is currently no insulation in the cavity.

If the cavity was uniform and large enough I would put a cavity closer in but its not straight or wide (almost touching in places)

I have offcuts of celotes and loft roll?

Thanks

J

 

A bit of celotex/expanding foam then normally dab board over

 

There's no point insulating it, after all the extension and the main house are both going to be the same temperature.

Is the top of the cavity insulated over? If it were open at the top, which isn't unheard of, then it would allow heat to dribble into the cavity and escape into the world. The floor would too but I'm guessing it'd be negligible.

 

Yes you should its more about preventing a cold bridge/condensation/mould etc than heat loss. In any case the cost and effort to fit it is negligible.

 

Thanks for replies.

As I said I will struggle to get anything substantial in the cavity.

I might just push some celotex in and foam it up.

Many thanks

 

Thats all it needs to prevent cold bridging.

 

If the wall being knocked through is an internal wall, the reveal does not need insulating.

If the wall remains an external wall, it needs a vertical DPC and then some ridgid insulation of any sort, expanding foam, or quilt and then gobbed up with mortar or plaster.