Double joists - how to fix together?

[pilsbury]

Putting 8x2 joists in for my flat roof on hangers. I'm doubling up the joists either side of the roof lights (using a double width hanger). How do I secure the joists together? M10 threaded bar, nuts and washers? Spacing? Or just 4" screws? Not going to be a lot of shear stress seeing as they are both supported together?

 

[Doggit]

Either would be fine, but if you use screws, grip them together first so that the screw doesn't push them apart.

 

[^woody^]

M10 bolts, 600mm centres, staggered horizontally at 1/4 depth ( one high, next one low) with a spur washer between the joists.

Or coach bolts, same principle.

The idea is that the load is shared and the joists act as one.

 

[tony1851]

Why is it necessary to double up the roof joists?

 

[pilsbury]

Why is it necessary to double up the roof joists?

They are single joists (400mm centers) throughout except either side of the rooflight which is 70kg and 800mm wide. Extra support for the added weight and "missing" joist

 

[tony1851]

They are single joists (400mm centers) throughout except either side of the rooflight which is 70kg and 800mm wide. Extra support for the added weight and "missing" joist

What's the span of the joists?

 

[pilsbury]

4.4m

 

[tony1851]

4.4m

Oh, double-up it is, then!!