Goal post design.

[G and J]

On the back of our house we will have a 3m single storey bit with a flat roof.  The rear face of this comprises a 4.1m set of patio doors flanked by two little stubs of wall.

 

We've been advised that we need some ‘goalpost’ style steel to provide racking strength, which I can easily understand.  What I can’t work out is if it is better for this steel to be tight to the patio doors, or is it better to have it full width, i.e. into the corners.  
 

 

I can imagine that option 2 is better from a cold bridging point of view but I can also imagine that I’m missing some other fundamental factors.   Comments appreciated.  

[DevilDamo]

If the external returns/corners are big enough, you should not require a goalpost frame but just a beam across the top. The second option will definitely require a goalpost frame but you should also consider how the cavity side walls would meet and integrate with the columns.

[G and J]

1 hour ago, DevilDamo said:

If the external returns/corners are big enough, you should not require a goalpost frame but just a beam across the top. The second option will definitely require a goalpost frame but you should also consider how the cavity side walls would meet and integrate with the columns.

My understanding is that they aren’t big enough, they’re only about 2’ either side, hence steel being unavoidable.  
 

If the goalposts are in the corners, then methinks, I can thicken up the timber frame between the post and the patio door and reduce the effect of the cold bridging?

[Russell griffiths]

I would set the posts100mm back from the opening, you can then screw a stud to the side facing the door, this could be clad in some form of ridgid foam and then the door fitted, it will provide good fixings for the door and isolate the steel from the frame. 

[G and J]

3 minutes ago, Russell griffiths said:

I would set the posts100mm back from the opening, you can then screw a stud to the side facing the door, this could be clad in some form of ridgid foam and then the door fitted, it will provide good fixings for the door and isolate the steel from the frame. 

Like this you mean?

[Russell griffiths]

Sort of, you could bring some insulation down between the door and timber also. 

[G and J]

8 minutes ago, Russell griffiths said:

Sort of, you could bring some insulation down between the door and timber also. 

Good plan.  I assumed I would have to screw the frame straight to the timber.  Ta for that.

[Russell griffiths]

1 hour ago, G and J said:

Good plan.  I assumed I would have to screw the frame straight to the timber.  Ta for that.

Most of the weight goes down, your frame should be fixed with straps, not screwed through the frame

straps come out the back face and to the timber, then cover in insulation and plasterboard 

[Alan Ambrose]

What you don’t want, of course, is the goal posts moving