The base of my workshop is constructed with mortise and tenon, and rabbet joints.

The mortise and tenon (left) ensures the base stays completely rigid without the need to secure it to a foundation. In this particular build I used a method called "draw pegging" which was necessary because the beams are not dry. A problem with using this joint on wet or "green" lumber is when the lumber dries, it shrinks, and eventually the joint becomes loose. Draw pegging is where holes are drilled into the tenon one-sixteenth to one-eighth of an inch (1.5 to 3 mm) short of the holes in the mortise. When the pegs are driven in, the offset holes will draw the joint together extremely tight and allow for shrinking. As a bit of an aside, regardless of what type of wood is used (spruce and poplar in my case) the dowels are always made out of a hardwood, most commonly oak.

The rabbet joint (right) is simply a pocket for a beam to sit in. I have not found any literature on a dimension ratio between pocket and beam size, but what works for me is to cut the pocket height half of what the beam height is, and then then cut the depth the same dimension. In this case, a four by six inch (102mm by 153mm) beam will have a pocket cut four inches wide by three inches deep and three inches high. Lastly, a shoulder is cut so the beam fits in the pocket. No fastening is required because this beam supports the floor, and the weight of the floor is plenty enough to hold it in place.

Both joints roughed out with a chainsaw and finished with a chisel.