Doubling up rafters

[HammieUK]

Posted this in 'Floors, Stairs and Lofts' but this is probably a more suitable forum....

I'm planning on installing a couple of roof windows in my loft, since I'm cutting 2 rafters I'll need to double up the side ones, however there's a couple of purlins that prevent me from getting full length rafters in. How would one go about doubling these up? The only way I can think of is to nail it in 3 parts, then nail in another 2 parts across the joints. Any other ideas?

Cheers

 

[catlad]

I have fitted lots of velux and have only doubled the rafters by the side of the window unless I was doing the whole roof and if you put your trimmers in first you can nail through the side of the single rafter with 4"or 5" nails for a good fix

 

[^woody^]

You only need to double the rafter sections between the purlins, not the whole rafter length