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.
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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