Fix kingspan to kingspan NOT the normal

[aveatry]

I an trying to find a way to screw one piece of kingspan to another to build a insulating air gap in my loft so I can push the fibreglass insulation all the way up to it without compromising the air gap it will be like the photo

but taller and the 3 box sections you see will be 50mm kingspan and the flat bit they are attached to will be 25mm kingspan.
The reason is that I have a 12inch section above the window external wall that is a sloping ceiling, the bedroom sort of gos 12 inch into the loft 1960s house so from the loft there is a 4 inch deep (rafter depth) x 16inch width ceiling joist width sloping area that has no insulation.
My plan is to fabricate a 30inch x 16 inch stand off to push down this gap from the loft, the stand off will keep the 25mm pushed against the plasterboard and also allow me to push the fibreglass up to it without going over the air gap and at the same tinm I will be insulating the hard to reach area with 25mm kingspan.
So with what shall I fix the 50mm kingspan stand off blocks to the 25mm kingspan, I am thinking of some sort of very wide thread screw. Any ideas.

I hope I have explained it well enough

 

[Ian H]

Would it not be better to use 50mm timber for the standoffs?

 

[aveatry]

Would it not be better to use 50mm timber for the standoffs?

Yes that would solve it but I was thinking of something non rotable. And I already have some spare 50mm kingspan
I suppose that the screws only need to hold it all there while I push the contraption down the gap.
What has the widest thread - would it be single thread chipboard screws ?

 

[foxhole]

Expanding foam adhesive, you can also use wire coat hangers , cut and shaped to a large U for mechanical fixing.

 

[aveatry]

Expanding foam adhesive, you can also use wire coat hangers , cut and shaped to a large U for mechanical fixing.

Coat hangers - good idea

 

[aveatry]

Thanks everyone for there help. In the end I used beefy 5x60mm single thread screws, single thread looking a little more chunky.
Here is the whole project https://www.diynot.com/diy/threads/insulate-sloping-ceiling-from-loft.491007/