"Norminn" wrote in message
m...

I'm not a roofer or carpenter, but have one thought aboutt this.
Skylights often leak, so the reasoning
may be that if there is a leak and rot later on, doubling up will help
ensure strength and support of the
roof.

Skylights leak, simply because they're not installed properly. I had one
architect tell me all skylights leak, he wondered why I looked at him like
he had 4 heads. Then I explained about installation.

Doubling up rafters offers nothing. If this were the case, every
penetration would need doubled up rafters. Such as vents, soil stacks,
chimney flues, etc. Take a peek in your attic, you'll not see a doubled up
rafter at any penetration, unless you have an over-sized chimney spanning
several rafters.

When installing skylights, you do need to put blocking between the 2
rafters.

People tend to think because the sheathing ends at a skylight, you need
double rafters. If this were the case, you would need double rafters on the
entire structure, since sheathing starts at the eave & ends at the ridge.
In other words, it has to start somewhere, and end somewhere, and there's
no blocking at the eave or ridge.