Masonry block chimney
I would like to put up masonry block chimney with a clay liner. Any information on installation from footings to cap.
A check of local fire and building codes in your area should be your first stop. In most areas code requires that masonry chimneys have a minimum cross-sectional area of 50 square inches. Have a minimum clearance of 1 inch from any combustible material. This 1 inch air space must be filled at each penetration of floors or ceiling with a non-combustible material like fiberglass insulation or plaster.
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If your chimney is to be built outside of the house your footing also must be placed below the frost line in your area (normally where frost is a problem this is between 4 and 6 feet down). Your footing should be twice the width of the block you are laying and I recommend 12" thick. Measure 8" or one block from ground or floor level put in a cleanout door next determine what height to place your thimble (where your stove pipe enters the chimney)local codes vary on this also rule of thumb says 18" below ceiling to top of pipe.Once this is determined measure down from the ceiling 18" plus diameter of the stove pipe plus 12" this is where you start your flue liner. The best way to do this is to get some cement brick cut them so when laid they project into the chimney to the inside of the flue liner without leaving too much of a ledge inside. Laying the next chimney block will keep them in place and support the flue.
A second course of brick will offset the joints in the flues and block. Cutting the flue liner is complicated if a pre cut one is available take it. Fire clay for your flues should be an air set type because normal chimney temps won't be high enough to set heat set material. Your flashing should be in two parts one L shape under the shingles and up the sides of the chimney one out of the chimney and down to within 1/2 to 1" of the sub flashing or shingle. The chimney should terminate 2' above the highest point within 10' of the chimney(unless local code says different).There should not be more than 8" of flue exposed above the cap.
When pouring the cap wrap the flue with fiberglass to leave about 1/2" expansion (caulk later with fire proof caulking)and mix the concrete as dry as possible to prevent cracking.
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