In message , GB
writes
On 7/23/2016 3:50 PM, 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?

That must be correct, unless the walls below are not fully in contact
with the truss, or at least not taking much weight. As Harry says, one
way to achieve that is to fully load the truss before building the
studwork partition walls. I suppose the real question is what's under
the partition walls, and can that take part of the roof load?

Surely the roof load is carried by the outer walls and simply
stretches/spreads the floor component.

Houses are generally built with so much reserve strength that you can
get away with all sorts of mess-ups like this.

It is a bit academic anyway as the thickness turns out to be the same as
was used when the rest of the house was build in 1995.



--
Tim Lamb