Plasterboarding RSJ

[AverageDIYerEssex]

Hi all.
I have just had a hole made in the back of my house, RSJ fitted and bifolds installed. I was going to stick some batons to the underside of the RSJ and then fix plasterboard to that (as I needed to fill a 2inch gap at the top. However, I am now looking at fitting blinds so need that 2 inch of height so the blinds aren't too low and don't sit too much in front of the top of the doors.

I wondered what your thoughts are of adhering the plasterboard directly to the underside of the RSJ (inside obviously).
My initial concerns are is the RSJ will get so cold (as it obviously runs through to the outside of the house, albeit the edge covered with render) but if it will get so cold that it would generate moisture inside which will effect the plasterboard stuck to it. I don't want to do it all and then start getting damp in.

what are your thoughts?

 

[DAZB]

Cut timbers, say 4 X 2's or 6 X 2's to the height of the web plus the bottom flange of the steel and notch them so they house over the bottom flange so effectively sitting flush to the base of the RSJ but wedged into the steel. You then have fixing points for using plasterboards to fix to and remember it ought to be double skinned fire resistant plasterboards. This video shows the method...

 

[AverageDIYerEssex]

Nice one thank you. I saw that a while ago but forgot about it. I'll do that.

What's your thoughts on the RSJ getting cold and getting wet and transferring to the plasterboard? Is it something that happens?

 

[DAZB]

There could be some aspect of thermal bridging but it should not be wet. If you can get even an inch of insulation below it then do so otherwise you can get the super thin wall insulation on a roll which will be minimal but is at least something.

 

[AverageDIYerEssex]

There could be some aspect of thermal bridging but it should not be wet. If you can get even an inch of insulation below it then do so otherwise you can get the super thin wall insulation on a roll which will be minimal but is at least something.

'thermal bridging'... just by saying this phrase I know you know your stuff lol.

thank you.

 

[cdbe]

and remember it ought to be double skinned fire resistant plasterboards.

Can you clarify the requirement for double skinned fire resistant plasterboard? Personally I was under the impression that the requirement is 30 minutes, achieved by standard 12.5mm plus skim

 

[DAZB]

From memory and also checked on my current spec from my architect with my own ongoing home renovation which states ....
"• Steel beams to have 50 x 50mm cradles and two layers of 12.5mm fireline plasterboard lining with 5mm gypsum plaster finish."