To be able to handle live loads, we recently reinforced the 2x6 joists in our attic by sistering them with 2x8s. To achieve level, the 2x8s are not flush with the 2x6s on the bottom; they range anywhere from 1/2 inch to 1 1/2 inch higher.
The question is then how to apply the guidelines for drilling electrical holes. When they say to stay "2 inches away from the top and bottom" does that apply to both boards individually or just 2 inches away from the bottom of the 2x6 and 2 inches away from the top of the 2x8?
Here's a cross-sectional view of the worst case scenario:
Holes are for wiring only; so 3/4" - 1" in size is all that's needed.
So the question is: How far down from the top of the 2x8 should I drill a 1" hole?
If I drill the hole so it starts at 4 1/4" down, this leaves 2" of 2x8 below the hole, but only 1" above the hole on the 2x6.