Insulating a Catnic lintel

[marty3]

I am on a mission to stop draughts and increase efficiency whilst redecorating. I am about to put plasterboard back up over a catnic lintel that looks like this...

I have noticed that you can get catnic lintels that have a polystyrene filling, I was thinking of either stuffing it with rockwool or filling it with expanding foam.

Anyone see any issues with doing that?

 

[^woody^]

Go for it.

 

[siwriderby]

You’d be better off using insulated board around it than insulating inside it. It won’t do any harm putting insulation inside but in reality any heat just travels around the steel and the inside doesn’t provide any benefit; so you’re better off stopping the heat from escaping through the wall to be honest.