Hello Norseman,
I just now finishing a project that would lend itself to you current poarch project parameters, has been PE approved twice, and I also teach timber framing along with other traditional skills. Feel free to send me an email, and we can go into more details of your project, goals in further learning timber framing, and more specifics of your project.
Now, to your current questions:
I will be using timbers we have sawn ourselves (woodmizer bandsaw mill) (spruce)
More than acceptable for a small porch project.
Keep the slope low ish (I'm thinking 5/12)
I work in "Asian design" parameters typically so 3/10 to 5/10 pitch is a normal range for "Engawa" and related veranda/porch profiles. 4/10 (22°) is my preferred on most of this type, and almost exactly the same as a 5/12 pitched roof.
Display as much timber as possible.
Keep the room free of obstructions (no knee braces protruding into the room.
Even today, in most Chinese, Korean and Japanese frame modalities the frame is often exposed inside and out, especially in the roof systems. This being a porch, the frame will be completely exposed for viewing. Further, there is not "oblique bracing" in Asian designs, except for some of the "bracketing techniques" in the roof systems, and a few esoteric methods of "oblique bracing" found with "stitch beams," related corbel braces, "horizontal obliques" in the roof and foundation framing (these are always out of the way for normal ingress/egress patters of use) and other unusual methods.
95% or more of the pricing is achieved through proper and specific joinery and "horizontal modalities" such as "Nuki beams." All of this lends itself well to many "modern aesthetics" and not having to contend with "triangles" that can obstruct views, movement, and fenestration withing wall systems.
I am currently away from my computer and typing this on my phone. Once I get to my computer I will post a link to my sketchup design and post snow load info for the area.
If you could send that in your email, it would be helpful.
The structure is to be 28'8" by 16" with the trusses spanning the 28'8". I have 3 trusses spaced 8' apart.
That can get extended to 4 to 5 meter (I work in metric) instead of 2.4 meter (~8") if the design is modified accordingly.
We plan on using either 2x12 or 12"tgi joists 2' on center for the purlins.
I would wait to see your Sketchup CAD before going into detail on this aspect. I would add here that "2x" stock is not part of typical timber framing for most designs accept perhaps in some of the "Nuki beam" frame work. Most stock ranges from 75 mm x 75mm and goes up from there. The mean average in size is 150 to 200 mm square (~ 6" to 8".)
The roofing hasn't been decided yet but I'm guessing metal. I currently have the 2 end trusses designed as a simple kingpost with webs. The center truss they wanted more height to mount a light or fan from so I made it a scissor truss with an arch cUT inot thw bottoman chord. Both truss types have 8x10 top and bottom chord with 6x6 king post and webs.
I am using 10x10 posts and beams in the walls. 3 posts on each end under each truss. I plan on using standard framed walls to in fill between the posts.
The post size is rather large and I would only go that big if that is the "aesthetic" one cares for. The "cord" assemblies appear over built as well, unless the lumber is of much lower grade than typically yielded by spruce ssp.
1. Are my trusses good enough
2. Will the plywood on the infill be sufficient lateral wall bracing.
3. What is the r value of 8" and 10" of timber. (Wondering if I can display the timber inside and out, or if I need to inset and cover with some type of insulation).
4. Will drilling a 1" hole vertical through the center of the ridge and king post affect the structure of the scissor truss.
5 I'm sure as this design/discussion/build goes on I'll have many more questions.
I would have to see the CAD model to address specifics further.
I am sure you will also get much more wonderful feedback here from the collection of members.
Warm Regards and again Welcome to the TFG forum,
j
