Part of a renovation I am planning involves removing a partition wall in a single-story ranch with a gable roof (roughly 4/12 pitch, framed with 2×6 Hem-Fir, built 1965) in the northeast with a designated ground snow load of 35 psf.  While the wall is not load bearing (the ceiling joists are single-member), the joists do rest on it, which cuts the span of the ceiling joists so it falls within acceptable limits. Without the wall, the ceiling would sag and potentially put undue stress on connections.

What I’d like to do is essentially support the ceiling joists from the rafters so I do not have to put a beam in. The plan so far is to run (2) 2×6 strongbacks across the center of the span of the ceiling joists that would be connected to the rafters with (4) 5/8in diameter, 11tpi, ASTM A307 Grade A steel threaded rods tied into the rafters with collar ties placed just below the ridge board. Each collar tie would consist of (2) 2×6 doug-fir fastened to each side of the respective rafter. I am also considering adding a couple of 2×4 king posts along the run of the strongback to add some rigidity and compressive strength to the system.  Attached is a drawing (not to scale) of the proposed support system with dimensions and connection details. 

The length of the ceiling joists are 23 ft and the room (running perpendicular to the ceiling joists) is 20.5 ft long. According to my calculations (written out on the attached drawing), the mid-ceiling tributary has a 230 plf load and the total load of the mid-ceiling tributary is 4,715 lbs. The tensile strength of each rod is 13,560 lbs, and all four will have a cumulative tensile strength of 54,240. The double 2×6 strongbacks are capable of carrying 756 plf over a 4 ft span (from each end of the end wall), but will mostly be there for distribution of load across all ceiling joists and to add stiffness. I am aware that I could build a more elaborate and stronger truss system, but I like this system for its simplicity, cost effectiveness, and accessibility (I will be running electric and ducting after installing the system). Plus the threaded rods allow me to easily lift the ceiling joists if need be after removing the partition wall. 

I am confident of the ability of the system to support the ceiling joists, but am a bit unsure about the added load that is being transferred to the rafters. With a rafter span of 11′ 6″, my rafters are slightly undersized by today’s standards (2018 IRC span table prescribes max span of 11′ 1″ – which I know are well on the conservative side ). I could add rafter ties halfway up the height of the roof to counter potential deflection, but would like to avoid that if possible. The older (and wiser) builders I know are not concerned about the additional load on the rafters, and a JLC article about snow loads on roofs (which says that rafter breakage is quite uncommon on pitched roofs, most roof failures from snow loads are caused by connection failures, and that snow design loads are conservative) lessens my concern (but makes me want to take a closer look at the rafter connections!). I wasn’t able to find any examples online of anything like this being done, so I thought I’d put my situation up here and see what people have to say. Thanks in advance for any help!