The concept of runnning the joists over the tie is a no-brainer--
a good solution especially in an outbuilding. Kind of like the old dutch barn style temporary loft joists-- they just threw up some poles over the anchor beam to add seasonal hay storage.
I suppose you could make this work in a house frame as well.
I personally like dovetail lap tenons, but think making every joist or purlin tenon a dovetail is unnecessary. I usually make 2 of them dovetails-- spaced 1/4 in from either side. Overkill for sure-- nails and subfloor will tie everything together way more than the dovetail tenons will, but I like that there is some joinery performing that function for the long run. Basically I look at it as a nice touch that doesn't really take that much more time.
Wedging seems to work best with pine joists-- they squish and I imagine the squished part doesn't continue to shrink. I also cut frames seasonally in the outdoors-- it takes a couple of months to cut and raise, normally in the summer, so things have a chance to dry quite a bit.
I'm no hemlock hater myself. Shake and splinters aside, its cheap and versatile. Looks beautiful planed in my opinion. Pine works much more nicely, but hemlock has that sort of satisfying crunch when you chisel it. Every wood has its virtues and vices. Hemlock is the wood of choice around here for boarding, strapping, and studding. Its pretty much the only choice for local studs. Put 'em up green though, or not at all.
