Best/easiest method for sistering/doubling up rafters/joists

[Cory H]

For doubling up rafters/joists to make a trimmer or header for a stairs/roof window, I see a few ways recommended in the forums:
- Bolting with M10/M12 at 600 centres with a toothed timber connector between members
- 10d nails at 100 centres
- Grade 6 100mm screws at 150 centres
If the timbers are also glued together, are bolts overkill and manual nailing unnecessary (as there will be little shear). Am I right then thinking that screws at 150 centres (alternating between top and bottom thirds of the joists/rafters) are the best option or am I missing something? Thanks

 

[tony1851]

Screws would be perfectly OK spaced as you suggested. (Consider 80mm screws as 100mm will poke through and result in blood everywhere).
No need to glue (glue and screws have different characteristics and don't 'work together') though it certainly won't do any harm - just a bit messy.