I don't have any picture to help you guys so ill do my best to explain it. I'm building a cabin next summer(30'X24'). Its a hewn log cabin, with a knee wall on the second floor. My question is about the joint i should do to connect my 2nd floor joist to my summer beam(center beam) and the hewn logs. I have a 12"x12"x30' summer beam supported by two 8"x"8 post at the distance of the 10 and 20 feet mark on my summer beam. My joist are 6"x10". The joint i was thinking doing is a "L" shape mortise and tenon with a shoulder.
l------5"-------l
l----3.5"--l
___________________ ________________
l l
6" l l
l l
l l
l l
_______l l Summer beam
JOIST l _______l
4" l l
l l
___________l l
____l
l
2" l
l_________________________
So it would be a tenon of 3.5" long with a shoulder of 1.5" for a total length of 5". The tenon would be 6" high and the bottom part of the joist that sitting on the shoulder is 4" high. So basically with both joist on each side it leave a 2" untouched in the center of the summer beam. What do you guys think of that joint length? The joist doesn't really need to be flush with the summer beam it could be higher but i don't want it on top of it either. Do you guys think I'm taking too much out of the beam. Do you think that whats left under the shoulder (2") is not enough? (cause i think so)
And the joint on the hewn log would be a basic 4" deep pocket(the hewn log is 8" thick) to sit the joist in.
The 2nd floor will be 2"x4" and 2"X6" tongue and groove.
the summer beam is white pine and the joist are red pine.
I hope you guys understand what I'm saying!!!!!! :o
Thanks!!!!!!!
From what an engineering professor tested and presented on at a TF Guild conference last year, the effective beam left is a 2x12. The untouched width X the depth
Don, if the joist tenon was 6"x6"x6", with a diagonal from the 6" to the 10" dimension, that would still give you just about full strength on the joist, correct? This is the standard joist layout that I've encountered. A shorter joist tenon, say 5", would give you still more of your summer beam left. You would loose your housing, however.
Dave
Hey! Check out the wording on this post ::). Are you trying to get the feds to watch this site? ;D Some stoner just did a search on google on how to roll a joint and ended up at the forestryforum. Maybe we'll get some new members.... :D
First of all you're talking about a drop in floor joist to connect the hew summer beam to an outside wall plate.
If the first joint selected will compromise the strength of the summer beam then that may not be the best joint to use.
Is it possible to assemble the cabin with a tenon joint on the end of the joist going into the summer beam and a drop in joint on the other end?
If this would work you would cut a horizontal mortise in the summer beam to support the joint on that end with a housing if wanted, and then the other end could have a drop in standard floor joist joint.
Cutting a horizontal mortise into the summer beam to connect the floor joist makes the summer beam stronger has the top surface isn't cut, and therefore the cross section is not reduced to a point where the beam may fail.
In my gallery, I found this example of a floor joist with tenon:
(https://forestryforum.com/gallery/albums/userpics/10095/Tying%20joist%20tenon%20drawing-with%20dimensions.JPG)
And there are other pictures there of tusk tenons that could be used.
Jim Rogers
Jim Rogers, so if the horizontal tenon is 2.5 or 3" thick by 6" wide do you think that is strong enough to support a 2nd floor?
Don't know without running all the numbers, for joist spacing and span and floor loads.
A lot goes into the joint design.
The above example was just to show you that tenon can be made instead of drop in joists.....