Thanks marcel.
I agree with Marcel that it’s really not about area. In practical terms it’s really limited to buildings about 35 feet wide (40 foot max, but that requires other than typical materials), with conventional framing and connections, that are not irregular in shape or in a high wind/seismic zone.
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Wow… old thread. Here’s one where I get to answer me… six years later!
If it looks like somone has tried to copy manufactured trusses, using 2x4 or 2x6 and plywood or OSB gussets, recommend an engineer.
Post and beam trusses are often assembled onsite to drawings supplied by an architect.
FYI
My dad and I built a garage back in the mid seventies exactly as you describe from drawings provided by the package provider.
They were very similar to the photos here and the plans specified how many nails held the gussets in place.
I probably would not call for a structural engineer without evidence of a problem after several decades.
If I called for an engineer every time I inspected stick built roofing frames, trusses they would not be able to keep up with the work load. I would guess roughly half the homes here particularly down town and East Hill area are 50 yrs and older. Most have survived dozens of major hurricanes and severe tropical storms over those years and show no signs of going quietly. Tight as a drum and not a hurricane clip in sight. Most are made from old heart pine and cypress. Some of the beams and timbers are as straight as a rifle shot and the quality of the workmen in those days still shows through. I did a house over 100 yrs old last year down in the historical district with 6 x 6 beams underneath where they did not use any fasteners. All mortise and tendons with the sharpest joinery you ever saw. No bowing, cracks, checking or even blemishes. I approach each house individually, try not to assume anything about it and just report in as simple terms as I can what I observe. I never editorialize the report findings. I have found many new homes with engineered trusses that needed to be bulldozed and started over. I have found trusses that may have been engineered but the quality of the wood was so inferior it should never have been used for anything except for firewood. Just my two cents.
Roof framing! Just one more system in which it’s difficult to say anything generic that’s true everywhere. I don’t see that many site built trusses here and the ones I do see are often pretty bad.
Some of the old homes here (100 yrs or so) have great work and some don’t.
I think if you are in an area where there were good craftsmen, people who did shoddy work had trouble finding work. I’m guessing it’s truer in the
Eastern US in which “old” is a lot older than places farther west. 100 years ago there weren’t any 100 year-old homes in Colorado, but a lot in cities on the east coast.
I really like looking at the older stuff because you have to get into the mind of the builder and see how they made decisions and solved problems. I took a course in CO called “Stepping into in the Boots of the Builder” about assessment and stabilization of historic wood structures. Out here, it was barns. Along the edge of the plains, every 30 miles or so there was another sawmill and local builders who worked their area. You can recognize individual building methods and tool marks if you get to see anough places.
Nice break from the same old thing.
Doug, are these conventionally-framed roofs built using 2x4 (common here too) or attempts to build roof trusses onsite?
Heavens no! These old conventionally built roofs, frames and such hardly ever have a 2x4 in any of it and for that matter no nominal sized lumber. At one time Pensacola was a major export port of lumber (lots of old growth pine, etc.). They shipped lumber all over the world out of here. Now days, only wood grown locally is for paper. Shame too. There were some massive logs brought down the rivers from the northern parts of the counties. There are a few guys that still harvest some of the old logs out of the rivers and bayous. The smallest I think I have ever seen is true 2 x 6s but most are larger beams and timbers. That old wood is almost black from age and hard as iron. You can not pull a nail out of it with a crowbar, you just end up giving yourself a charliehorse or a hernia.
The building code does not specifically forbid the use of site built trusses provided that they are designed by accepted engineering practice and a design drawing meeting the the 18 requirements of IRC chapter 8 section 802.10.1 is submitted too, and approved by the Building official prior to installation. With that said here in Florida by State statute the design must be approved by the engineer of record before submitting to the Building Official
King post truss field built.
Not to old, cause the plywood gussets are nailed with an air nailer.
King post trusses were limited to 16’ span, first thing to check is bearing under the king post. It might have been built like this for erection only.
Gussets in the late sixties and early 70’s would have been 5/8" plywood and not 1/2 like appears to be here.
Nails would have been 8 penny and clinched.
Also the picture shows very poor attempt on the rafter tail extensions.
What is the age of the building?
Ken
Here is an example of an attempt to build a home made truss. One of the key concepts is the arrangement of the web members should form triangles. If you look down the truss you see a vertical web all by itself. This truss went out over a porch and that vertical web member rested on the exterior wall of the house. The typical triangle pattern truss web members make stiffens the entire truss by distributing the forces. If you interrupt this triangle pattern by a poor design or a broken member forces are not distributed properly and #$@! happens like this photo.
That’s a good picture and example Randy of a framer not knowing the design concept of a wood truss design nor how it reacts.
Chord placement are totally wrong and rafter should have been a 2x6 if in a snow load area.
That’s the worst attempt at truss design I’ve ever seen, Randy! 
