Except in the dry climate of the Rocky Mountain region it is customary to fur all outside brick walls (that are not built hollow) with 1x2-inch strips, nailed to the walls vertically and set 12 or 16 inches on centres. These strips can generally be secured by nailing into the joints of the brickwork, using two nails close together if necessary. Very often thin strips of wood are built into the inside of the wall at intervals of 2 feet to form nailings for the furring. These strips, when used, should not be more than 3/8 of an inch thick, and their use is not desirable and should not be permitted in buildings over two stories in height. (See Section 255, Part I.) Where stone walls are to be furred or " strapped " it is necessary to "plug" the walls to form the nailings. This "plugging " is done by raking out the mortar and driving in wooden plugs about J inch in diameter and 4 or 5 inches long. The plugs should not be more than 2 feet apart in the length of the furring strips.
To plug a wall takes considerable time, and unless the walls are quite high it is usually about as cheap to set 2X4-inch studding inside of the wall, securing it to the floors at top and bottom, although this of course takes up a little more space than the " strapping."
Whichever method is pursued the furring should be put up plumb and true, so that the walls when lathed and plastered will form a true plane. Inside brick or stone walls are better not furred, as the furring necessarily leaves an air space which affords room for the passage of flames and vermin, and the plaster can be applied to brick or stonework as well as to lathing.
Where there are to be inside shutters it is often necessary to " fur out" or thicken the wall to form the pockets. If this increase in thickness is 2 inches or more, the furring should be done by independent studding and should be particularly described in the specifications. All studding for furring should be bridged for stiffness and to keep it in place, as described in Section 69.