Beam for load relief - which dimension?

[lano]

I have a similar problem myself. I need a beam right under the trusses on the lower floor to support the dead load from the upper floor (because surely, snow load etc. are taken up by the outer walls). To the question; what load should one account for and how much deflection can be tolerated (construction-wise - not aesthetically)?

The distance between the outer walls is 9.6m, and the clear span is 6m with columns and 8m without. What dimensions do you think are needed, and what do you think about placing two beams next to each other?

 

[Magnus_Redin]

I have a similar problem myself. I need a beam right under the rafters on the lower floor to take up the dead load from the upper floor (because surely the snow load etc. is taken up by the outer walls).

If there are interior walls that can transfer load from rafters to the upper floor, they will transfer load even if both rafters and outer walls would suffice if the interior walls were not present.

 

[lano]

There is an internal wall above (at least 4 meters). Is it possible to make the wall on the upper floor load-bearing in some way, i.e., that it "supports" the underside of the roof truss (the floor joist)?
Are there any "rules of thumb" for the loads that should be considered?