I have a residential remodeling client that wants to modify existing conventional 2x4 hem-fir triangular shaped trusses to scissors style trusses to create a vaulted ceiling. They do not want to remove the existing roof deck/roofing to install new trusses due to cost and weather. Is it practical or cost effective to modify these trusses to include new bottom chords and diagonal bracing along with gussets to create the scissors style truss? Or is it more practical and cost effective to design a conventional rafter system with or without a center bearing wall? Here is some existing data and a photo is attached:
Truss horiz. span to bearing walls = 26 feet
Truss vert. height at center = 46 inches
Code live (snow) load is 40PSF above 7000 ft. elevation
Code dead load is 15PSF
Truss members are 2x4 hem-fir, 1968 construction, good condition.
an interior bearing wall (bearing on a slab on grade) is possible below the truss centerline since it is consistent with the proposed floor plan and would be perpendicular to the roof framing.
I've done a search function and found some similar discussion, but the result was to remove most of the roof decking, except near the bearing walls to allow installation of new engineered scissors trusses from the exterior.