Tim Lamb wrote:
One for the structural engineers...

The architect has specified manufactured dormer trusses. When I asked
him to supply a drawing for the manufacturers, showing the two
studwork partition walls which are below the new timber (90deg.
roughly midway), he said it was not necessary as they are not load
bearing.
Now I was only ever electrical but they still made us do applied
mechanics. A simple beam carrying a load has to deflect whether the
load is distributed or not. Any deflection must cause some of the
load to be carried by the walls below?

Nope, it's all carried by the exterior walls, including the pre-calculated
deflection.
When we put trusses up on newbuild houses (big 5 or 6 bedroom houses) they
go on before any internal walls, or even floors are in place.

The truss manufacturers will build them based on the measurements of the
exterior walls and what's going on top, tiles, slates etc