Article and photos by Gregory Havel
Most firefighters correctly assume that a fire built in a masonry fireplace will stay inside the fireplace unless the fireplace has not been maintained, has not been cleaned regularly, or was not built properly. Other reasons for a fire include deliberate or accidental human activities like using the wrong type of fuel, failure to close the fireplace screen, and placement of furnishings and decorations too close to the radiant heat.
Photo 1 shows a masonry fireplace constructed in 2007. It is on the first floor of a two-story lake cottage of lightweight wood-frame (wood I-beam) construction. The weight of the masonry fireplace, hearth, and chimney is carried by masonry foundation walls in the basement that rest on the building’s footings, not by wood framing or structural members. The wood framing and structural members are separated from the fireplace and chimney by the distances required by National Fire Protection Association (NFPA) 211, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 ed., incorporated into the state building and fire codes.
The fireplace in Photo 1 is nearly complete. A brick hearth separates the fireplace from the hardwood floor boards. Brick masonry on the front separates the firebox from the drywall board, wood mantelpiece, and wood trim to be installed later. Part of the steel framing that supports the brick arch is visible on either side of the fireplace. The firebrick in the firebox has been laid in a running bond on the bottom and sides and in a herringbone pattern in the back. The natural-gas igniter for the wood fuel has already been installed.
Photo 2 shows this same fireplace earlier during construction. The firebrick has already been completed to the bottom of the clay tile flue liner. One of the corrugated galvanized steel masonry ties (visible at the left of the photo), is used to connect the firebrick to the decorative brick masonry at the front. Note that the horizontal steel tension member supporting the ends of the brick arch is enclosed by brick masonry to protect it from radiant heat. Also note the steel lintel supporting the firebrick behind the brick arch. The plywood form for the brick arch and the wood spacers between the bricks will be removed after the mortar sets and cures, and any defects will be patched with more mortar.
Photo 3 shows three sections of the clay tile liner used inside the masonry chimney, to protect the concrete masonry units (CMUs, concrete blocks) and bricks from the heat. These sections of liner are available in dimensions for most sizes of chimney. Lengths may vary, depending on the size of the liner and its weight. Usually, the mason sets the liner sections so that the joints between liner sections will not align with the mortar joints in the concrete block.
For detailed requirements on the construction of masonry fireplaces and chimneys, see NFPA 211, especially Chapters 7 and 11. Chapters 13 and 14 cover inspection and maintenance requirements.
The most common problems firefighters encounter with fireplaces and their chimneys include the following:
- Deteriorated masonry chimneys.
- Masonry chimneys built without clay tile liners.
- Wood framing and other combustible materials installed too close to the outside of the masonry fireplace or chimney.
- Ignition of creosote and other combustible deposits inside chimneys and flue liners.
Books on the construction of masonry fireplaces are available from several publishers. Many contain good information and proven formulas and dimensions for safe and efficient fireplace and chimney construction. However, most of them are not updated as regularly as the NFPA and other codes and standards. As a result, masonry fireplace and chimney construction require careful coordination of proven designs with current building and fire code requirements and careful inspection during construction.
The condition and maintenance of masonry fireplaces in public buildings should be added to the fire inspector’s checklist; and are public fire education topics for homeowners.
