Valley rafter installation height?

[Digmixfill]

Merry Christmas everyone.

 

I have two roofs at the same pitch and height that join with a pair of valleys that will have valley tiles. Common and jack rafters are 44mm wide, and valley rafters are doubled up.

 

I'm looking at valley rafter installations, and I see some valley rafters set at the same height as the commons and jacks. I see some where the jacks are slightly higher than the valley rafter, so I assume the valley rafter is set lower than the commons in this case? What I have failed to find is any information giving an indication why either variant is used. Is there a reasoning behind the choice?

 

 

[Oz07]

It's just because the valleys are on a lower pitch so the plumb cut is higher on the main plane of the roof.

[Digmixfill]

My common rafters are at 35 degrees, and I expect my valley to be somewhere near 26 degrees.  Are you saying that if I cut the heel height of the bird's mouth the same on the commons and the valley rafter, the valley will naturally be lower than the main plane of the roof?

 

 

 

[Oz07]

In this case I doubt it will be noticeable. It normally happens more when you have a bastard valley. The ones you see are not purposely setting it lower they are just keeping the internal line set flush to the rafters

 

Think of it if you cut a 6x2 at 10 deg it will be near enough 6" across the cut, cut it at 45 degrees and will be a lot longer. 

[Digmixfill]

If I'm going to screw up anywhere with the roof it will be the valley rafter. If the height difference to the main plane is in the hardly noticeable class for my particular case, I'll cut the bird's mouth as the other rafters and adjust if necessary. 

 

Thanks Oz

[Oz07]

Research height above plate. That's what you're trying to match if you want to keep everything in plane up top.