This term is commonly used to designate work that is built out from the constructive members to receive lathing or metal work and sometimes sheathing or finished woodwork. It is also sometimes called " false work," as the surfaces which it forms are hollow and do not indicate the actual construction.
In fireproof buildings all furring should be done in tile or metal, as described in Section 357, Part I., but in all other buildings the cheaper grades of wood are used for the furring and in small pieces, as they generally have to support nothing heavier than lath and plaster.
There is usually but little furring on the outside of buildings; the blocking for the cornice or belts and the furring for metal work or for curved roofs being about all that is generally required. On the inside, however, considerable furring is often required for the lathing in the way of strapping the walls and ceilings, furring out brick and stone walls, and in forming false beams, arches, coves, cornices, etc.
This inside furring is usually done immediately after the roofing is on and while the outside of the building (if of wood) is being finished.
For furring stock cheap grades of pine or spruce are used in the Northern and Western States, pine being preferable because it warps and twists less. The stock may be rough, but where it is used for cross furring, etc., it is better to have it dressed to an even thickness, which adds but little to the cost.
Cross-Furring of Ceilings. - In many sections of the country it is the common custom to "cross-fur" the ceilings or under side of the floor joists with 2 or 2 ½x 7/8inch strips, as shown in Figs. 59 and 60, but this custom is not universal (see Sections 46 and 76), and if the floor beams were all dressed to a pattern there would not be much advan tage in cross-furring. As it is, the principal advantage of cross-furring is that it is more practicable to get a level ceiling by it, and the floor beams may be spaced from 14 to 18 inches apart, while the bearings for the laths may be spaced either 12 or 16 inches, as desired, without much additional cost. Even if the bottom of the beams were all on a level when set, some will bend more than others, and, as the furring is put on some time after the beams are set, this unequal de flection may be in part overcome. On the other hand cross-furring leaves a space between the bottom of the floor joists and the laths sufficient for the passage of vermin and of fire.
When the ceiling is to be cross-furred no particular care is taken to have the floor joists level on the bottom, as any inequality may easily be overcome when putting on the furring strips. This is done by cutting the bottom of the beams that are lower than the average and blocking up those that are high, as shown in Fig. 183. In putting up the furring a strip is first put up at one side or at the centre of the ceiling and carefully leveled from end to end, and the other strips are all leveled from that by means of a long straight-edge and a carpenter's level. The usual size of the strips is 1x2 inches ; if the joists or rafters are more than 18 inches apart the strips should be
1 1/8x2 inches. In all first-class buildings the strips should be spaced 12 inches on centres, although 16 inches is the more common spacing because it is a little cheaper. The strips should be well nailed at every bearing with 10-penny nails (cut nails hold best). Where the under side of the roof forms the attic ceiling the rafters are cross-furred in the same way as the floor joists.