Should there be a lintle?

[Andy198587]

Hi, we've removed a balanced flue gas fire, and want to keep the hole in case we put it back at a later date. My question is should there be a lintle above the opening? It was a new build house, and they have just chiselled the thermalite blocks and then made the flue hole in the outer wall. We are just going to use some plasterboard and vent it to seal it up, please see attached pics. 2nd pic shows the top of the opening behind the plasterboard. Thanks Andy

 

[snowhead]

Yes there should have been, but it may be higher up and that's just a block to fill the gap.

No surprise if it's one of the large House Builders

 

[Andy198587]

Yes there should have been, but it may be higher up and that's just a block to fill the gap.

No surprise if it's one of the large House Builders

Thanks for that had a reach up behind in the cavity, once I got all the insulation out( now looks like it snowed in here) I can only feel breeze block joins at least another row up so I'm assuming there probably isn't one there.
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I'm now thinking it will be easier to just brick up outer skin and use some bricks to fill the hole on the indide, would this be deemed as an acceptable way to close the hole up?