It is frequently necessary to afford buildings temporary support in consequence of the instability of the walling, caused either by the removal of adjacent houses, by faults in construction, or by defective foundations.
This support is obtained by propping up such walls as are likely to be unstable with balks of timber called "shores."
Shores may be used singly, as shown at A, Fig. 386, or arranged in groups of two or three, according to the height of the wall to be supported.
The arrangement at B is a double shore adapted for walls of moderate height. Three shores are used at C, where the wall is higher.
Another combination of those shores, shown at D, is adapted for cases in which long timbers are scarce.
In all these cases the shores are placed in an inclined position, their feet are fixed firmly on the ground - or, if that be soft, are made to abut on blocks or thick planks called "footing pieces," buried in the ground; these distribute the pressure, and prevent the shore from being forced into the soil.
When two or three shores are combined they are secured together by means of cross pieces of plank, a a, nailed on each side of the balks; the feet are strongly bound together with hoop iron, h h.
The upper end of the shore abuts against a thick plank placed against the wall extending over the height required to be supported, and secured as follows (see Fig. 387) : -
Holes from 4 to 6 inches square are cut through the plank and into the wall behind it; through these are passed pieces of scantling, N, called "needles," which, being about a foot long, enter the wall some 4 or 5 inches and project about the same distance from the outside of the plank, thus forming an abutment on the top of the shore S, wedges, w w, being inserted so as to make up for any opening or inequality in the joint. Wooden cleats, C, are generally nailed above the needles so as to give them additional strength.
In cases where one or two houses are taken out of a row the external party walls of those remaining are supported by horizontal shores of different forms, such as those shown in Fig. 388.
If the opening be narrow and the height to be supported moderate, as at A, Fig. 388, the shore may consist simply of a horizontal balk connected with struts abutting against planks, which serve to distribute the support over a greater height of wall, and may be secured to it by needles as above described. When the walling to be supported is higher, a combination of two such shores may be made, as shown at B, Fig. 388.
If the opening be of considerable extent the shoring may be of a more elaborate character, forming deep trusses, as at C, Fig. 388, placed at intervals of a few feet throughout the depth of the buildings.
When a passage is formed between two houses and they have to be strutted apart permanently, the shores may be of iron, such as old rails, bent and secured in a form similar to A, Fig. 388. •