Lath, in building, a long, thin, narrow slip of wood, which is nailed on the rafters of a roof, in order to support its covering.

Laths are divided into three classes, according as they consist of different kinds of wood: viz. 1. Such as are formed of heart of oak, and which are used only for tiling; 2. Sap; and3. Deal-laths-, both of which are employed exclusively for ceiling and making partitions. They are farther distinguished, with respect to their length, into,five-feet, four-feet, and three-feet laths, though the statute allows only laths of two lengths, namely, those of five, and three-feet : each of these is directed to be an inch and a half in breadth, and half an inch in thickness.— For an excellent method of laying laths, so as to make them tfireproof the reader will consult p. 281 of our 2d volume.

Laths are sold by the bundle, which is generally called a hundred ; it should be observed, however, that seven score, or 140, are computed in the hundred for three-feet laths; six score, or 120, in such as are four feet in length ; and for those which are denominated five-feet, a full hundred, or fivescore.