Orientation of Floor Joists

[m63]

Hi,
Is there a role of thumb for orientation of wood joists in tree storey building? I am thinking that floor joists oriented parallel with roof trusses makes sense from a lateral load resisting point and this orientation usually requires less load bearing walls but usually see them oriented perpendicular to orientation of roof trusses and with more load bearing walls. Should this be just joist span/depth economic consideration or there are other - structural things to consider?
Thenks.

 

[FalsePrecision]

The former premise is not true. The orientation of any framing is primarily for economy-the long joist, short header/girder philosophy.
However, in some cases, a value engineering can include other factors, such as orienting the framing in a way to drastically reduce shear wall holdowns due to increased dead load on a shear wall.

 

[RockEngineer]

Sometimes if you orient the joists and roof trusses in the same direction you will overload the bearing wall and foundation in framed construction. Having the joists run opposite the roof trusses distributes the load more evenly on the foundation. Whether this is economical depends on the geometry of the structure.

 

[FalsePrecision]

When you are using sawn lumber joists such as 2x10, it makes sense to frame the joists in the direction which has consistently shorter spans. When you are using a pre-manufactured floor truss or composite joist(plywood web and laminated lumber flange), and have liberal allowance for maximum depth of floor truss/joist, it is much more economical to frame in the direction that has the longer spans.
The load on bearing walls is usually not critical. You can alwaysspace studs closer than the usual 16" o.c if needed by calculation.

 

[m63]

Thank you all for your input. Seems there is no widely accepted role for floor joist orientation.