Fire Regs for Steel - Fireboard thickness

[Spinny]

Plaster boarding going around a steel. The steel supports a 2.2m opening in the back wall of a 2 storey house.

Wondering whether the fire protection requirement (would it be 30 mins or 1 hour ?) can be met with a 12.5mm fireboard. ?

The problem being that the rest of the wall has already been boarded in 12.5mm, so using 15mm will create a problem with skimming the wall.

 

There is 70mm of rockwool between the 44mm studs in front of the steel and therefore immediately behind the plasterboard.

Edited July 21 by Spinny

[Mr Punter]

Yes, 12.5 will give 30 mins.

[Spinny]

Has got 15mm fireboard underneath. Got a call in with Building Control.

[nod]

As above 2 story =30 minutes