Fixing plasterboard to steel beam- which method pls?

[Safety First]

Hi all,
Old timer builder (no disrespect meant) that installed 5 inch wide steel beam has bolted 2x2"s into voids (of the 'i' shape), then fixed treated battens horizontally to fix plasterboard to.

My issue is that 2x2's plus battens project about 15mm over steel edge. Apart from making steel look even bulkier this means we will have beam stepping over plaster of the nib wall which 'tells' of the beam, unless we want to plaster all the way down both sides of the nib. One side will have to be built out to accommodate cable going over steel edge.

I have heard from a.n.other plasterer that (shallower) battens can be flush to steel and fixed as follows; screw large plasteboard piece to one side battens, score (not cut through) board along inside bottom edge of steel and fold board under (option here to add gripfill to underside of steel) then score again and fold last side of board up and onto other sides battens. Add tape and profile.

Old timer baulking at this suggestion and has no ear for my wish to have narrow(er) finished item. Says anything other than his way will fall off. Said steel sweats etc.

Building control have only specified fixing of 12mm board. Any thoughts please ?

 

[noseall]

Steel beams should be double boarded or fireboarded.

We always take into account that the pillars or nibs will need attention to overcome the added thickness, i.e. remove skirting boards and wall paper etc and make good. Always ensure that the plasterboard carries over vulnerable joints. Try and stagger the plasterboard joints.

Bolting timber into the web is good practice.

 

[Safety First]

Thanks noseall. Double skin was planned until building control said as it's domestic a single skin is fine. How to attach is the issue. If you have experience of the scoring method, have you known it to fail -fall off?