Preservation by Prevention: Historic Masonry Chimneys

Ca. 1710 Massachusetts house with a central brick chimney with a corbelled cap

Ca. 1710 Massachusetts house with a central brick chimney with a corbelled cap

Now that fall has truly settled into the Washington area, the cool, crisp evenings and weekend afternoons have me hankering for a cheery, wood-burning fire. Luckily, a previous owner added a fireplace and chimney to the house. It’s something we can tell is a later addition because the brick is slightly different from the main body of the house, and none of our neighbors has a similar chimney. The house has a second chimney, which is original, that vents hot gases and exhaust from the mechanical systems.

We had the chimneys inspected for cleanliness and soundness over the summer. The fireplace chimney is clean and in good shape, but the chimney that vents the mechanicals is a different story. We were told that the flue liner in the mechanicals’ chimney had disintegrated, and that the masonry chimney was also losing integrity. It was time for me to learn a bit more about chimneys and their maintenance, and I am now pleased to share my findings with you.

The Getty defines chimneys as “vertical noncombustible structures containing flues for drawing off into the outside air products of combustion from, for example, stoves, fireplaces, and furnaces.” The chimney, then, is the structure and is most commonly constructed of brick or stone. It surrounds a flue or a group of flues that carry exhaust gases up and out of the building. The flue itself is a passage and should be surrounded with a flue liner, which is – like the chimney – constructed of noncombustible and heat resistant materials. To see a Chimney diagram, click here.

Chimney History

Exterior end chimney, Carvill Hall in Kent County, Md., Library of Congress, Prints and Photographs Division, HABS MD,15-FACR,1-3

Exterior end chimney, Carvill Hall in Kent County, Md., Library of Congress, Prints and Photographs Division, HABS MD,15-FACR,1-3

Before the advent of modern methods of heating, whether by furnaces, radiators, or heat pumps, fireplaces and stoves were the primary method of climate control. A chimney’s masonry mass allows it to capture and retain heat effectively. In cold climates, this was a benefit because the chimney helped heat rooms that did not have fireplaces or stoves of their own. In warmer climates, however, chimneys that vented cooking fireplaces radiated unwelcome heat in the summer months. Without air-conditioning there was only one way to combat this unwanted effect.

Historically, builders accommodated the local climate and heating needs with careful placement of the chimney. In New England and other locales with colder climates, chimneys were often located at or near the center of the house, where they could radiate heat in all directions. Many of these original chimneys can still be seen piercing roofs and ridgelines today.

In warmer areas, chimneys were commonly placed in “exterior end” positions, meaning that they abutted the sidewalls but were external to the house, which minimized the heat gain caused by using a fireplace. Another option was to locate a chimney in an “interior end” position, which means that the chimney was contained within the structure’s sidewall. This position moderated the amount of heat radiated to the interior but permitted more heat capture than an exterior chimney.

Chimney Maintenance

To ensure proper chimney maintenance, you should monitor its cleanliness and structural soundness. Have your chimney regularly swept and cleaned by a professional in order to prevent fires caused by creosote buildup. In addition, regular checks and repairs of the chimney’s bricks, mortar, crown, and flashing, as well as installation of a cap, will help ensure that it has a long life. The crown and cap prevent water from entering the top of the chimney, while flashing prevents leaks where it meets the roof. Even with proper maintenance, however, the chimney itself can fail, as can the flue liner.

Ca. 1930 Virginia house with interior end brick chimneys

Ca. 1930 Virginia house with interior end brick chimneys

Chimneys sometimes lean, either along their entire height or just in the portion that extends beyond the roof. If the entire chimney is leaning and pulling away from the building, or the foundation is settling differentially, you should call a professional mason and/or structural engineer to evaluate it. The chimney may have to be entirely rebuilt. If reconstruction is necessary, and it is at all possible to reconstruct the chimney with original bricks, then it is preferable to do so.

If the chimney is only leaning above the roof, and the main shaft of it remains plumb and level, a condition problem caused by exposure to wind, rain, and freeze/thaw cycles is indicated. These forces will deteriorate the mortar, which is softer than the brick, particularly when water has infiltrated an uncapped chimney. When the mortar erodes, it destabilizes the brickwork. Again, you should consult with a professional mason, but it may be possible to repair the chimney by rebuilding only the portion above the roofline.

Not all historic chimneys had liners, and until the turn of the 19th century many, in fact, did not. For those that did, the liners were most commonly made of terra cotta tiles. Unlined chimneys are a fire hazard because the hot gases eventually corrode and destroy masonry and mortar, exposing combustible materials that will burn from constant exposure to extreme heat. If your flue was never lined, or the flue liner has disintegrated, you should have it relined.

The three most common options for flue relining are cast-in-place concrete lining systems, stainless steel, and galvanized or aluminum sleeves. Certain lining materials are only compatible with specific types of fuel, and the liner will need to be sized to the firebox and/or appliances it serves. You should discuss these requirements with your chimney professional before selecting a system.

Once you have had your chimney inspected and cleaned, and repaired any defects, you’ll be ready to light a fire on the next cold night and turn on your furnace with confidence. Just remember to have it checked annually and to stay on top of the necessary repairs and cleaning.

Image used in this newsletter:

Perspective View of North and East Elevations
Photographed by Randolph Langenbach, 1973
Carvill Hall, Fairlee, Kent County, Md.
Library of Congress, Prints and Photographs Division
HABS MD,15-FACR,1-3, Survey Number HABS MD-867

For Additional Information:

The Chimney Safety Institute of America

Disclaimer: This newsletter is intended to provide a non-expert reader with basic information. For professional advice, please consult architects, contractors, and/or engineers. If you own a property encumbered by a historic preservation easement granted to the Trust, we strongly recommend that you discuss any proposed maintenance plans with Trust staff to determine if approval by the Trust is required.