You could also say "the heck with all this noise" and use 2x8 #1 for the bottom chord, and 2x4 STUD for the webs and have no worries. You can also look up on-line any number of standard, simple, truss designs that will take into account your location. This also has the benefit of letting you know the proper grade of material - I'd think that, if anything, you and I would likely tend to under-spec the bottom chord grade, and over-spec the web grade. Especially if you tell them you want to buy the all the lumber and hardware from them - its not like the truss suppliers and building supply houses are exactly overwhemled with work in SE Michigan these days. 'Collar ties' are defined in the International Residential Code (IRC) in Section R802.4. If you went to a builder's supply place that sells engineered roof trusses, I think that - for a nominal fee - they could get the whole thing designed for you - it would take maybe 30 minutes on the modern design software their truss supplier uses. But in a DIY situation, pounding in large nail plates is a thankless task, so I personally would go with the longer board. Top flange designed to interlock when used in pairs so that rafters maintain correct alignment. Easier and stronger than toenailing or screw fastening. In fact - I can almost guarantee that most of them would default to a spliced bottom chord - 2 8' or one 6' + one 10' - because shorter lumber is cheaper than longer. The RR ridge rafter connector provides a connection between a rafter and the ridge of a roof. In fact, I'd guess the engineering design software would actually come out with 2x4 top chords and 2x3 webs including the weight and snow load issues you correctly pointed out - but your're not about to replace the top chords. In a truss, 2 x 6 top chords and 2圆 bottom chord with 2x4 webs would easily handle a 16' span. You need to consider the weight of the wood and finishing materials being added to your existing rafters with the anticipated snow load the roof may see.All true. 16' is far too great a span for 2 x 6 materials unless the structure is a properly designed truss.
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