This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
149. When adjoining buildings have been built originally with party walls, or walls supporting the floorbeams of two buildings, and one of these buildings is to be torn down, the adjacent walls should be prevented from falling by spreading braces or inclined shores. When there are buildings on each side of the lot on which the new building is to be erected, the walls of these structures may be supported by spreading braces.
150. When the distance is not more than 25 feet, the braces may be arranged as shown in Fig. 58. At a are 6"xl2" uprights against the walls d, to distribute the bearing of the braces; at b are the spreaders, and at c the angle braces, all of which may be 8" x 8" timbers.
When the old buildings are from 40 to 50 feet apart, the spreading braces should be trussed, as shown in Fig. 59.
The 6"x12" uprights are shown at a against the walls e; the 10"xl0" spreaders at b; the 8"x8" struts and braces at c; and the vertical iron or steel ties at d. It is preferable to use iron or steel rods for these vertical ties, as they can be readily screwed up, and thus overcome any sagging that may occur in the joints of the truss. One truss should always be placed in the front, another in the rear of the building; and an intermediate one every 25 feet between will generally be found sufficient.
When there is no wall opposite the building to be braced, inclined shores or spur braces may be arranged as shown in Fig. 56, but with a greater inclination. Iron or oak wedges should be used at the lower ends of the braces, to give them a proper bearing. These spreading braces are usually built by the carpenter, but it is essential for the architect to know how they should be constructed.