Splines and corner joints

[Was_Yeah]

Hi everyone,

I'm a beginner working on a small project, a playhouse on stilts for my kids, similar to this.  



I'm not using that plan, but it's the gist of what I'd like to build.  The reason I link to it is that the way I'm thinking of joining the tie beams that define the floor of the "loft" portion is the same as the plan. It's appealing to have the tops of the (tie?) beams all be coplanar, like the plan does, so I could lay down plank flooring wall-to-wall:



Now my questions: the plan appears to use a spline to join one of the beams coming into each post, and a "regular" tenon to join the other beam.  It looks like you could use a tenon to join both, or at least, I don't see what extra the spline gives you, since it doesn't extend past the bottom of the beam, and the amount of material removed from the post seems the same wither way.

What's the advantage of a spline here?  When would one choose a spline vs a tenon in a context like this?  Is this a reasonable way to join these beams to each post, or would one of you recommend a different way?

Thanks in advance, it's been fun to lurk here for a few years.

[Don P]

I don't get the spline either ???.

Look at the roof support beam. The rafters rest on an unnotched beam. 
Then look at the floor beam. It isn't a good idea to notch it if possible... or it needs to get bigger somewhere.

How about dropping the front and rear beams below the joists with them resting on the lowered beam. There can be a notched rim capping the joists. The load bearing beam carrying the joists is unnotched, it just has end tenons and rest on a ~1" table.

 The joinery in the posts is then offset, win/win, somewhat. Technically (grading rules say "defects" within 6" of one another is the same combined defect.) It is better from that standpoint though.

[Was_Yeah]

Thanks Don!  I'm glad to get your confirmation about the splines, as I don't know what I don't know a lot of the time.

And I appreciate the suggestion about offsetting the floor/loft beams and resting the joists on them without notches.  Are there any special considerations there?  How do people typically fasten the joists to the beams, or do they at all?  (Searching for "joists" here got me a lot about joist pockets and other things, but not much about this apparently-simpler case.)

[Don P]

I guess these would be offset, haunched, tabled, beams. Just the way I'm envisioning it. The post would be stronger if the tenons did not project through the far side. I've carved out an angled (haunched) table about an inch wide for the beam to sit on so that the load is on that whole beam width. Notice I just said a 1 deep able. Code states that minimum bearing on wood is 1-1/2". TF'er's traditionally make tables 1" and preserve more post. An engineer would quantify load and check bearing area on that shelf and modify if needed. Anyway, I'm trying to spread the damage to the post out over more area.


 

 Hangers are not the enemy. Simpson makes heavy beam hangers that would work here and because of less damage from screws mounting the hangers. Heavy hangers can put beams at the same level without compromising the post. You can hang joists on a beam without notching and weakening the beam. At this point I'm making the rim joist non load bearing, it can be a notched heavy timber, blocking, or a nailed on 2x rim joist. It is providing lateral stability to the joist ends, bending is handled by the beam under the joists.

[Don P]

I sketched in the rim joist, one of the joists, and an empty joist pocket. That can be moved inboard for insulation outside the rim. The rim or blocking is simply roll prevention for the joists so anything that does that, not a real high calling. Doing it this way doubles the shrinkage induced floor settlement, look at that stack of horizontal timber. Use the driest material you can.



 

[Was_Yeah]

Thanks Don!  I can visualize things a lot better now.