Additional Loads
Question:
I am a structural engineer designing pool cage structures that are typically attached to the house at the fascia board. Sometimes, the structure is attached where trusses are behind the fascia board and other times there is a framed gable end overhang. Do you know of any information concerning this additional load on the trusses or overhang under design wind loads? Is there a limiting distance on the amount of overhang? I know trusses are designed for certain uplift and the pool cage will add to this uplift at design load, but what about the gable end overhangs? Are there any calculations regarding the amount of uplift they can take?
Answer:
Assumptions cannot be made regarding loading and uplift without knowing the original design and the assumptions on which it was based. Most truss design software does account for wind uplift at overhangs and cantilevers, per specifications – but only when wind loading is specified by the building designer. We contacted an engineer of one of the plate manufacturers and he stated that he does not know of any standard limits governing overhang or cantilever length beyond those limits resulting from standard structural design procedures (strength and deflection limitations). Regardless of the overhang or cantilever distance, the truss or the element of the truss that the fascia board is attached to, the uplift connectors fastening the truss to its supports, or anything else in the load path could be at its maximum allowable limit prior to any further application of load from a pool cage structure. The only way to be certain that you are not over-stressing the truss is to find the original truss and building design or repeat those design calculations.