This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
While the walls are being built the carpenters have been at work framing the house and are now ready to lay the sills and put on the first floor beams. The preparation of the sill consists in halving and pinning together at the corners (Fig. 18), mortising for the door and window studs, and notching out for each floor joist about two inches down into the top of the sill. The sill should be well painted on the under side as a protection against moisture from the wall, but unpainted elsewhere to allow of drying out, and should be set in a thick bed of mortar. As our sill is to set back two inches from the face of the wall, we shall have a chance to point up with mortar along the outside edge to be sure that there is no chance for cold air to get into the floors at this point.
Fig. 18. Corner of Sill.
Custom allows much variation in the size of the sill, six by six being the more common size. Six by eight is called for in our case and in some cases the sill is made six by the depth of the joist. Where large sizes of timber are easily obtainable, this method is to be commended. In the first place the greater depth of timber will span all openings that are likely to occur in the cellar wall, again, the equal depth of the sill and joists leaves no space connecting the cellar with the vertical wooden wall and prevents circulation of fire or vermin without recourse to brick filling, (Fig. 19.) The sill may be bolted to the wall, but this is not usual except for light framing in exposed situations. After the sills are set, the next timbers to be put on will be the girders which support the inner ends of the floor beams. These are usually 6 X 10 inches or 8 X 10 inches for the floors of a wooden house; in bur case 8 X 10 inches, and they are generally set under the bearing partitions of the house, and supported by brick piers or iron columns in the cellar. These piers or columns are generally not set until after the heavy floor beams have been put on as they would be liable to be knocked over in handling the heavy timbers, so these timbers are usually supported by shores until the piers are built. The piers of the height of an ordinary house cellar should be 12 X 12 inches, spaced, according to the size of the girders, from seven to nine feet apart.
In their vertical position, the girders may be set flush with the floor timbers, in which case each joist is framed into the girder, or they may be dropped to allow the joists to rest on top, usually notched an inch on to the girder. (Fig. 20.) The advantages of the flush framing are that the shrinkage of wood at each end of the joists is equalized, that circulation of fire by means of the interior partitions is prevented, and that the girder does not take head room out of the cellar. The advantages of the dropped girder are that the full strength of the girder is available and that it is possible to run hot air and other pipes up in the partitions without cutting the girder. If flush girders are used the position of mortises, as well as the position of the mortises in the sill should be examined by the superintendent to see that the openings framed for chimneys, stairways, etc., are correctly laid out according to the framing plans. Obvious errors will, of course, be easily detected but it will save much annoyance later if every mortise is verified before the floor is put on. When this is done the floor timbers may be set. These are usually two inches in breadth and in our case are ten inches deep. Upon these joists is invariably laid, in the East, a rough floor of 7/8-inch boards either of spruce or hemlock upon which the workmen can move to carry out all subsequent operations. It has been the custom in the West to omit this under floor, but the saving is very slight and the benefits of the double floor are many. In the first place the under floor stiffens the building perceptibly, is of great convenience to the workmen, and allows the laying of the upper floor to be put off until the very last thing. This is an important consideration in these days of bare floors and has led to the adoption of the rough under floor generally. It is a good plan to lay this floor diagonally with the joists as it greatly stiffens the building and gives a more even surface upon which to lay the upper floor.
Fig. 19. Sill on Wall.
Flush Girder. Fig. 20. Dropped Girder.
Fig. 21. Bridging of Joists.
As soon as the rough floor is laid, and before this, if the boards are to be laid diagonally, the floor beams must be bridged, or trussed, as it is sometimes called. This consists in cutting in diagonally between the joists, strips of wood which are nailed securely top and bottom and cross each other between each timber. (Fig. 21.) Some carpenters reason that a piece of plank cut in vertically between the joists will serve the same purpose, but this is not so. If the floor is laid square across the joists, the usual way is to take up a board along where the bridging will come. The superintendent should look out that the bridging is well fitted and thoroughly nailed, and continuous from side to side.