=Supporting the Chimney= Stable foundations, preferably of concrete, should be provided, at least 6 inches wider all around than the chimney and 8 inches thick for one-story and 12 inches thick for two-story houses. When there is no basement or cellar (fig. 7, _A_), start the foundation of an exterior chimney well below the frost line; otherwise, extend the base to the same level as the bottom of the foundation of the building. Foundations for tall, heavy chimneys require special consideration. Where the wall of the house is of solid masonry 12 inches or more thick, the chimney may be offset and carried on corbels or masonry brackets instead of being carried down to the ground. The offset should not extend more than 8 inches from the face of the wall, each course projecting not more than 1 inch, and should not be less than 12 inches high. Often the corbeling is started at the second- or third-floor level so that the chimney is only one or two stories high. [Illustration: Figure 8.--For structural safety the amount of offset must be limited so that the center line, XY, of the upper flue will not fall beyond the center of the wall of the lower flue. _A_, Offsetting of the left wall of an unlined flue is started two brick courses higher than on the right wall so that the area of the sloping section will not be reduced after plastering; _B_, a lined flue showing the method of cutting the tile.] Chimneys in frame buildings should be built from the ground up or should rest on the foundation or basement walls if of solid masonry 12 inches or more thick. A chimney resting on or carried by wooden floors, beams, or brackets or hung from wooden rafters (fig. 7, _B_) is a fire hazard. Wood framing shrinks, and beams supporting heavy loads deflect in time. Sagging beams injure the walls and ceilings of the house and are apt to crack the chimney, rendering it dangerous. =Flue Linings= Although, to save expense, chimneys are built without flue lining, those with linings are more efficient. When the flue is not lined, the mortar and bricks directly exposed to the action of fuel gases disintegrate. This disintegration and that occurring from changes in temperature frequently cause cracks in the masonry, thereby reducing the draft. An unlined chimney is best if not plastered except at the sloped section (fig. 8, _A_). However, the vertical and horizontal joints should be filled with mortar and struck smooth and flush with the wall. Offsets or bends in flues (fig. 8) should not be greater than 30° with the vertical. This slope can be obtained by offsetting or corbeling each brick course only 1 inch.