Municipal building codes are more strictly enforced as they relate to fireplaces than they are for many other decorative additions in a house. The codes require the utmost in safety considerations because even when a fireplace is built exactly to code, it represents one of the biggest dangers inside a residential building. Always check with your specific municipal codes to make sure that you are not going to be in violation, whether you are installing a new fireplace or replacing one.
A minimum of 50 square inches is usually required for the diameter inside the chimney and flue liner and cross-sectional area of the fireplace. A metal stovepipe that is 8 inches in diameter will meet this code requirement.
Masonry Fireplace Inlet Thimble
Masonry chimneys must be equipped with inlets that have a thimble to prevent the connector from either pulling out or extending beyond the liner. The only exception to this regulation is flues serving fireplaces.
Walls made of brick chimney are required to be at least 4 inches thick. Chimney walls made of concrete block must be 12 inches thick.
Gas Shut-off Valves
Gas shut-off valves must not be located in concealed locations or a furnace plenum. The gas shut-off valve should be on the supply side of every gas meter and needs to be adequately protected from damage while still offering access for operation.
The height of the chimney will be dictated by specific local building codes, but typically chimneys are required to terminate at least 2 feet above the highest point of the building. This point must occur within 10 feet of the chimney in any direction outward from it.
Regulations prohibit two appliances from being vented into the same chimney. This means the addition of a fireplace cannot share the pre-existing chimney with a gas-burning stove.
Combustible Material Clearance
There should be at least 2 inches of clearance between the exterior of the chimney and any combustible material. In practice, this means that the chimney should be freestanding, with no wood framing attached to it. The gap between the roof and the chimney typically is required to be filled with a nonflammable plaster and should also be protected by metal flashing.
Combustible Material Surrounding Opening
Combustible materials that surround a fireplace opening are required to allow 1 inch of clearance for each 1/8-inch projection outward from the face of the fireplace. This regulation extends to any projection out to a distance of 12 inches. Wood molding 1.5 inches thick may not be any closer to the fireplace opening than 1 foot.