This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The term "partition" is applied in carpentry to the frameworks of wood, with their coverings of lath and plaster or their filling of brick or concrete, which are used for dividing up floors into rooms, when no solid bearing occurs upon which to erect brick walls, or when brick walls would be unnecessarily strong and expensive.
There are two kinds of timber partitions - 1. Common Partitions. 2. Trussed Partitions.
The sills and heads are generally made of 4 by 3-inch or 4 by 4-inch timbers. The studs are of 4 by 2-inch quarters, spaced at intervals of from 12 to 18 inches, according to the strength of the laths, and stub tenoned to the sill and head.
Nogging pieces 4 by 2 inches are cut to fit tightly between the studs, to which they are spiked in a horizontal position at intervals of from 3 to 4 feet. Nogging strips 2 by 3/4 inch, let into and spiked to the studs in pairs as shown at A, are sometimes used instead of nogging pieces.
The door studs are made 4 by 3 inches or 4 by 4 inches, greater strength being required to resist the slamming of the door, and to form a suitable fixing for the joinery work.
When the partition is at right angles to the floor joists beneath them the sill must be cut clear of the opening, the two parts of the sill being halved and spiked to the feet of the door studs.
Door openings are spanned by a 4 by 3-inch or a 4 by 4-inch head, housed and tenoned to the door studs, as shown at B, Fig. 274.
It should be noticed that all the timbers are of such a size that when framed together they all have a common face.
When a partition is parallel to the floor joists it should if possible rest directly upon one of them, which should be proportioned to bear the additional load. In no case should partitions rest upon the floor boards, as in the event of the floor being taken up for repairs the partition would fall. If a partition necessarily occurs between joists it should be carried on short pieces of timber or bearers framed between them.
The joists of the floor above a common partition should be given ample clearance of the head, so that in the event of the floor sagging no pressure may come upon the partition.
2. Trussed Partitions are of two kinds -
(a) Self-supporting Partitions.
(b) Partitions supporting Floors.
When the floors to be divided up cannot conveniently be made strong enough to resist the additional load from a common partition, self-supporting partitions entirely independent of the floor are erected. As beams, unless made excessively large, deflect under the influence of an ordinary load, and as deflection in the head and sill of a partition would cause the plaster to crack, these self-supporting partitions are trussed, - that is to say, the timbers are so disposed and jointed that the vertical loads are diverted to the abutments. In Fig. 275 it will be seen that the pressure upon the head comes partly upon its abutments and partly upon the tops of the posts and braces, whence it is diverted along the braces to the abutments of the sill. The load on the sill is partly transmitted to the posts from which it is suspended, and these posts in their turn divert the pressure down the braces to the sill abutments. By dividing a framework up in this manner into a series of triangles it is possible to carry considerable loads across large spans, and a little practice will enable anyone to overcome the difficulty of diverting forces over doors occurring in all sorts of awkward positions.
In designing trussed frameworks, care should be taken to so dispose the timbers that they may be subjected to either a direct tension or compression and not to a bending stress, otherwise they are very liable to fail.
When the partition is parallel to the floor joists the head and sill should be placed between them, and of course should each be in one piece; but if it be at right angles to the floor joists the sill must be kept well above them and made in two pieces, so as not to obstruct the door openings.
When floors have to be supported on partitions the framing is the same as in self-supporting partitions, save that the timbers must be larger and the braces more numerous to meet the greater load, as shown in Figs. 276 and 277. Horizontal timbers called interties are usually placed above the door openings, so that the loads may be more readily directed past the door openings and distributed more evenly over the supporting walls.
In all trussed partitions the head acts as a straining beam for the braces, while it forms a fixing for the posts and studs. In partitions supporting floors the joists are notched or cogged over their heads. The heads should rest at either end upon stone templates bedded in the walls at the bottom of a ventilated pocket, thus distributing the pressure over the wall and preserving the timber from decay.
Interties are used, as already explained, to facilitate the bracing, to distribute the load more thoroughly over the walls, to tie in the feet of the upper series of struts, and, when the partition passes through two floors, to support the joists of the middle floor, as shown in Fig. 277.