Safeguards Against Hazards in Chimney Construction
THIS subject has had but very little attention, but is of considerable importance in the prevention of fires. Many houses have been destroyed through the improper construction of chimneys, some through someone’s desire to save a little money, or skimp the work; some from lack of experience, but all through carelessness.
Chimneys when not built in the outer walls of masonry buildings, should be placed on a solid foundation of rubble stone or concrete in the ground below the frost line. The stack should be built of masonry, the surrounding walls never less than four inches thick, and where the area of the flue exceeds 300 square inches, the walls should be at least H inches thick.
Where flues are built in the outer wall? of masonry buildings, if chimney does not start at the ground, it should never be built with corbels extending out more than 8 inches from the wall line.
Never let the chimney support any part of the struc ture, such as joists, beams or girders. This practice frequently causes cracks due to the uneven settlement between the different parts of the building; and wood work very often becomes ignited when resting on or coming in contact with the chimney walls. Joists should be framed out around chimneys and kept at least 2 inches from masonry, and for open fire places should have a clearance of 20 inches. Many fires are due to the use of disintegrated mortar causing cracks. Never rest a chimney on wooden brackets, wood floors or posts, as wood shrinks, which also produces cracks, and woodwork may ignite.
Paper presented at Convention of Illinois State Firemen’s Association, Jan. 11-13, 1921.
A well constructed chimney should have fire tile flue lining which may be had in all standard sizes for smaller chimneys, and should be at least ¾ inches thick, be placed in the entire flue from a point below the lowest thimble hole to the very top of the chimney and laid in cement mortar. The smoother and straighter the flue, the better the draft. Some chimney builders put in the top length of flue lining and let it stick out a few inches. That’s “skinning.” All chimneys should be carried up from 3 to 5 feet above the highest point of the roof, and for larger heating plants 10 or 12 feet above the roof.
The following formula is often used for heights of chimneys: Divide the greatest inside diameter of the flue in inches by 4; then call the result feet and add 5 feet additional, which should give the required height of chimney above roof.
It is not good practice to plaster chimneys on tfte inside, as it falls off in time. Place thimble holes at least 12 inches away from wood lath and plaster ceilings and partitions; and for smoke pipes of a larger diameter than 6 inches, the same should be further away. When you do your spring housecleaning, don’t paper over the thimble holes without providing a suitable metal thimble hole cover so as to prevent a fire occurring from the heat from stove or heating device attached at some other part of the flue. See that smoke pipes fit tight into thimble holes and provide a good metal collar around same to avoid the emission of burning soot and sparks.
Wood furring and lath should be eliminated on chimneys; plastering may be done on the brick where the joints may be left in a rough state and with the use of good, hard plaster will make a durable job.
Avoid the makeshift type of chimney, such as sewer pipe, metal smoke pipe or other discarded scrap. Good chimneys will save many dollars, many buildings and many lives.
All of the above is intended to apply to chimneys for domestic use and for small heating plants where engineers and architects are not employed.