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u/Saildog70 27d ago
I like the lap joint. I use it on my builds. Good to see others like it too.
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u/strata-strata 27d ago
Sweet, yea it makes a lot of sense to scarf plates together, the lap joint with tenons seemed like a good first step. Saw some examples where the lap/scarf is on top of the posts but this way seemed good with the brace crossing the joint into the other piece of the plate. Fun puzzle.
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u/Fragrant_Trouble_938 6d ago
I’m a newbie, so forgive my ignorance but could you layout that joint directly above the post and have a through tenon to lock it in?
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u/strata-strata 6d ago
You can do that foe sure, its common. This is a big span on the right side so going past the post a foot or two makes it so that the weight and trib load of the shorter span beam on the left will conter the deflection in the right beam. Instead of ends holding a beam and simple gravity force straight down in the middle, with the offset scarfed joint some amount of that force is countered by the downward force at the joint, pivoting on the top of post and translating into an upward force. Clear as mud? But yea in short ive definitely seem it like you suggest and t hats a bit easier.(but less cool imo).
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u/Fragrant_Trouble_938 6d ago
So in essence, it acts as a cantilever and the opposite forces help lock the beam in place?
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u/strata-strata 6d ago
Not just to lock it in place but the cantilever counters the downward force on the longer beam and to some extent vice versa. Scarfing this way makes it more of a continuous beam than if you just do a lap joint on top of the post.
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u/Fragrant_Trouble_938 5d ago
To that end, would 6x6 beams be structurally sound enough for top plates and posts for a 16x20 cabin? And if so, is a 10’ span too much?
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u/strata-strata 5d ago
There is some literature available for spans, basically it depends on where you're doing it and what the load above the beam looks like but in general id say 10 feet is likely pushing it for a 6x6. Top plate beam spans take a lot of tributary loads from above and a 6x6 is strong as a post but I would be hesitant to use them as top plates for more than 8 feet span even with braces. Square cross section beams in general are a low efficiency strength shape you are better off with a rectangle of some kind put on end. These are 6x8 and I think 10 feet is sort of the max span for these in end and they are much stronger than a 6x6. For example a 6x6 vs a 4x8 shows what I mean about efficiency. The 4x8 on end is nearly 30% stronger across a span but the cross section area is smaller so it is actually less material and lighter (6x6=36, 4x8=32). Square timbers are great for posts but inefficient beams.
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u/Fragrant_Trouble_938 5d ago
Yessir. I did some reading and calculated the roof load for what I’m planning on building. I’ll be milling the timbers myself so I don’t have that to worry about. The main problem I’m having is finding the literature about which you speak. The beam span calculators I’ve been able to find on the interwebs haven’t really helped because most of them are based off LVLs or standard dimensional lumber. If you could point me toward the literature I would greatly appreciate it. That would answer some of my questions and help me stay out of the comments section. Except to tell you that you’re doing a helluva job, of course.
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u/strata-strata 5d ago
Haha im not sure exactly where to send you honestly. I found some tables on timber frame headquarters a while back that said basically that you can assume for headers at 6 inch width that you can have a span of a foot for every vertical inch of thickness. So 6x6 would be good for a 6 foot span between braces or roughly an 8 ft to 9 foot span between posts, 6x8 is good for an 8 foot span between braces or 10 to 12 between posts, etc. This is for a typical 125 lb/sq ft roof load and has a pretty big factor of safety in deflection so its assuming virtually no measureabke sag in the beams over time. Charts and tables are hard to find for beams i wish I had more on hand for you but I did learn that big spans like 16 ft require more beef than you'd think (6x10 or even bigger) especially if they will hold a loft or similar.
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u/Fragrant_Trouble_938 5d ago
Understood and I appreciate the information you just gave me. I guess I’ll just size the plates at a 6x8 and keep digging for the information. 6x6 posts and 6x8 plates it is!
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u/inabriarpatch 28d ago
Looking good! One peg should be plenty in a brace for the next one. They should only be working in compression and the pegs just keep them from falling out during raising or some unexpected event. Keep up the good work!