The connnection of the floor joists to the sill should be such that the sill will support the joist and without weakening the latter more than absolutely necessary; then if the foundation wall settles the joists will not move unless the sill does.
The ideal connection of joists and sill is by hanging the joists in a Goetz or Duplex Hanger, as shown in Fig. 24. This retains the full strength of the joist and suspends it securely from the sill.
The next best method, and the one more generally employed, is shown in Fig. 25. In cheap buildings, where only 4x6 sills are used, the floor joists are often cut as at a, Fig. 26, and the sill is not mortised. This is very poor construction, as it greatly weakens the beam, so that comparatively light loads will produce cracks as shown at b. A floor joist cut as at a, Fig. 26, and supported as at a, Fig. 27, will sustain less than half of the load it would carry if reversed and supported as at b.
The outer ends of the second floor joists are merely sized to a uniform depth and spiked to the top of the girt if a solid girt is used. Where a false girt is used the joist should have a notch about \ inch deep cut in the bottom to fit over the top of the girt, as shown in Fig. 18. Wherever practicable the joists should be placed so as to come against the sides of the studding and the two spiked together. The outer ends of the attic joists, if they rest on the plate, are merely spiked to it; if they rest on a false girt they are notched the same as shown for the second floor joists and spiked to the studding.
Framing of Joist to Girder. - When the inner ends of the joists are supported on a wooden girder it is cheaper and stronger to let the joists rest on top of the girder, but this often interferes with the headroom in the cellar and it permits of more settlement from shrinkage than if a flush girder were used. If the joists are framed flush into the girder, as in Fig. 28, they must be of ample size, and the girder must have sufficient width to offset the weakening effect of the mortise holes. The end of the joists should be cut as shown at a and a spike driven down through the top of the girder into the tenon. These proportions (which are in terms of the depth) give the greatest strength for both the beam and girder. Any cutting into a beam or girder should always be as near the centre line or neutral axis as possible, as the nearer the cut is to the edge of the beam, and particularly the lower edge, the greater is its weakening effect on the beam. Joist hangers such as are shown in Fig. 43 would, of course, be preferable to the mortise joint, but they are not often used in frame buildings. In those of the better class, however, it would be well to specify them, as they make much stronger construction, and the saving in labor largely offsets the cost of the hangers.
Fig. 29 shows the girder dropped 2 inches, thereby affording greater strength in the beam, but with the disadvantage of projecting below the ceiling; A shows the proper proportions for framing the end of the beam.