Elements of Stone Masonry

Chapter 5: Thickness of Walls

Foundation Walls  - A very good rule to fix the thickness of rubble-stone foundation walls is, that they shall be at least 8 inches thicker than the wall next above them, for a depth of 12 feet below grade or curb level; and they should be increased 4 inches in thickness below that point, for every additional 10 feet or less in depth. Thus, if the first story walls are 12 inches thick, the stone foundation walls would have to be 20 inches thick for 12 feet in depth, and 24 inches thick below that point for 10 feet or less. Rubble-stone foundations walls are seldom made less than 18 inches in thickness. A wall 18 inches thick is not always needed to carry the superimposed weight, but smaller walls are more expensive to build consequently are seldom constructed.

The thickness of foundation walls in all the large cities is controlled by the building laws. Where there are no existing laws, Table 1 will serve as a guide.

Stone Walls - The laws regarding the thickness of stone walls differ in the various cities, and no uniform rules can be given. For ashlar work, the New York law states that "where walls or piers are built of coursed stones, with dressed level beds and vertical joints the Department of Buildings shall have the right to allow such walls or piers to be built of less thickness than specified for brickwork, but in no case shall said walls or piers be less than three-quarters of the thickness provided fro brickwork."

The following regulations apply to the District of Columbia for rubblework: "Walls laid with rubblework shall be one fourth thicker than required for brick walls, but never less than 18 inches thick; they must be constructed with flat stone, sound and durable, laid on their natural beds, and brought to a level every 3 feet in height. They must be built between two lines, shall have bond stone or headers extending through the thickness of the walls at intervals not exceeding 3 feet, and shall be laid in cement mortar composed of 2 parts sand and 1 part of cement. No rubble wall shall be located as a party wall unless the written consent of the adjoining owner shall first be filed in the office of the Inspector of Buildings. The restriction as to location of the party wall above mentioned shall not apply to stone foundation walls which support brick walls."

For ashlar facing, the requirements for the District of Columbia are as follows: " Thin ashlar facing shall not be counted in determining the thickness of walls. If stone facing is used with bond courses alternately, not less than 8 inches thick, on the beds, the n such facing shall be counted as forming part of the wall, and the total thickness of the wall and facing shall not be required to be more than that herein specified for walls (meaning brick) but never less than 13 inches thick."