Your chimney doesn’t hold your house up. In fact, when your house was built, a hole had to be built in the roof and floors because the chimney was in the way. If anything, the chimney makes your house weaker. The roof and floors are not held up by the chimney. You can remove your chimney, and your house will stand up just fine. You might just want to plug the hole though, so rain and birds don’t come inside:)
Brick is not a structural building material. Brick is merely a veneer. It’s a siding. The walls of your home or even high rise buildings are not held up by brick these days. Almost always, there’s a wood stud wall in brick homes that is the actual structure. Instead of nailing wood siding to that wood stud wall, brick was used as the siding instead. Brick is really no different than wood siding: both are just a nonstructural veneer. It’s just there to protect the real structure from the weather.
Brick facades are spaced about an inch away from the actual structural wall, so any moisture that makes its way through the brick has a way of draining down to the ground. This space is called a “drain plane.” At the bottom of a brick wall, you will often see little tubes, screens, or gaps where any water that found its way through a brick wall can escape. These are called “weep holes.” Since you just learned a new word, here’s another brick-related word: wythe. A wythe is a stack of bricks forming a wall. It’s an old English word.
Back in medieval times, bricks did used to be structural, and a single wythe wall meant there was a single layer of brick between the inside and the outside of a house. Since brick and the mortar that holds it all together is somewhat porous, a single wythe wall was not very luxurious. Water could seep through, and there is no way to insulate a solid brick wall. A double-wythe wall means there are two layers of brick with an air gap between those layers. This gap provides a place for moisture to drain and likely not leak through the second, interior wall. It also provides a place for insulation to go.
Brick walls were structural when our limited engineering knowledge was as basic as: just stack things up and hope they stay. As buildings got higher over the years, the bricks got bigger, and/or the walls got thicker to provide a more sturdy base. Think about it: the pyramids were built of giant stone blocks just stacked on top of one another. Gravity pulls down, so a massive brick base can resist that force. That was the limit of structural knowledge back then.
Something that brick doesn’t support well is side-to-side motion from earthquakes and wind (lateral forces). When a brick building moves sideways, there’s nothing to stop the forces (like the ground works to resist the effects of gravity pulling downward). As brick moves sideways, each one starts to individually separate, and you can see this sort of structural failure when there’s a staggered separation in the mortar joints of bricks that looks like stair-step shaped cracks as it works its way across a building facade. This is sure-sign evidence of lateral failure (which means side-to-side movement).
Notice the two areas with thicker white mortar “repairs” that creates the telltale stair-step patterns of lateral failure where the unreinforced brick has separated over time.
To help to resist this sideways force, braces that look sort of like ladders made of metal bars are laid horizontally within the mortar “glue” between the layers of brick to help to join several bricks together since they are all “glued” to the same metal “ladder.” This is known as metal reinforcing. Brick facades without these metal reinforcing ladders are known as URM (unreinforced masonry).
Before metal was readily used or available, a row of bricks would be oriented on end with their short side facing out, so they could span to connect each wythe of a double wythe wall to unify each wall together to act as one. This was an early form of reinforcing. When you see a brick building that has a different orientation of bricks every ten courses (rows) or so, this is a sure bet that the building does NOT have metal reinforcing. You should stay away from these buildings during earthquakes.
Look closely! Notice the row of narrower bricks that are about 8 rows apart from each other. This is how they used to “reinforce” brick walls before metal braces were used.
This image also shows the row of narrower bricks spaced every 8 courses to act as reinforcing.
When these sorts of buildings are remodeled, it is common that building departments will require the building to be “seismically braced.” This means a steel frame needs to be erected within the brick facade, so the steel does the job of holding up the brick (properly). Needless to say, adding steel frames within existing buildings is VERY expensive. Tearing the building down to rebuild would be much cheaper, but often, old brick buildings are preserved because they are deemed “historically relevant.” Consequently, owners of old brick buildings face really expensive retrofit costs if they ever want to remodel their building. These are often project-stoppers. Even though everyone has good intentions when they want to historically preserve a brick building and make it more sturdy, the cost of doing so is rarely feasible for most people.
So, if you like brick, know that it’s just a facade in modern architecture. In historic architecture, it’s a beautiful burden because it’s not as strong as the three little pigs have made everyone think. The 2nd pig’s flexible house of sticks would actually resist the forces of an earthquake quite well:)
If you’d like to learn more about our design process, visit www.josharch.com/process, and if you’d like to get us started on your project with a feasibility report, please visit www.josharch.com/help
