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Buttressing: Definition & Effect

Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Architecture is a matter of practical as well as aesthetic concerns. In this lesson, we'll talk about one of the most common ways to provide structural support to stone buildings, and see how it's been used throughout history.

Buttressing

We're going to try an experiment. Go grab a peach. Now find the largest, heaviest dictionary you can and place it on top of the peach. Now go find a roll of paper towels and clean up that mess. If you look at the peach, you'll notice that it's not actually the bottom of the fruit that broke open. It's the sides. As the weight is pressed down on the peach, that force doesn't actually travel downwards in a straight line. It curves through the skin of the peach, pressing outwards as well. Peaches aren't unique here. In architecture, the weight of the ceiling not only presses downwards, but outwards as well. If the walls aren't strong enough to handle this pressure then they, like the peach, will end up making quite a mess. Luckily, we can do something fruit can't. It's called buttressing.

How Buttressing Works

At its most basic, buttressing is defined as creating supports to reinforce the exterior side of a wall so that it can absorb greater pressure from the force of the weight. Remember, buttresses (supports) have to be on the outside of the wall because the pressure pushes outwards as well as downwards. These supports are a practical way to increase the strength of a wall without making the entire wall thicker. After all, most people still expect to have windows or other forms of ventilation in their buildings. You don't always need thicker walls to create stronger buildings, you just need to reinforce those walls in the right ways.

Buttresses have been part of architecture for at least 3,000 years. The ancient Mesopotamians built stacks of stones at even intervals on the exteriors of their larger temples to reinforce them. As buildings got bigger and more complex, buttresses did as well. The ancient Romans were the first to systematically build using the arch, which more evenly disperses weight downwards and outwards, allowing for buildings that needed fewer interior support structures like columns. However, this placed more stress on the walls, so the Romans built more advanced buttresses. From there, the technique really took off.

Types of Buttresses

Apart from the simple use of vertical support columns along a wall, often called tower buttresses, there are at least five major types of buttresses you'll find in architecture, Most of these were more heavily used in the days of solid masonry construction than today. The first is clasping. A clasping buttress reinforces two walls at a corner by making the exterior of that corner thicker than the rest of the walls.

Clasping buttress
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A similar style of buttressing at a corner is with the angled buttress. This involves building each wall beyond the intersection, creating something that looks like a cross shape on the floor plan. Setback buttresses are basically the same, but instead of extending the wall at the actual corner, create extensions that are set back from it. The actual corner still looks like a normal corner. We've also got the diagonal buttress. While the angled and setback buttresses require two extensions, the diagonal buttress only uses one, which extends diagonally from the corner where the two walls intersect. You may notice that a great number of our buttresses involve corners. The reason for this is simple: corners are the weakest points where the pressure pushing outwards through the walls is most likely to break through.

Setback buttress
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The last of the five major kinds of buttress is perhaps the most famous. It's called a flying buttress, in which the vertical support column is attached to the wall by a half arch. The column is not directly against the wall, unlike in the other styles. The flying buttress is what first allowed medieval churches to go from being a few stories high with really thick walls to towering Gothic-era structures filled with windows. The most famous example is the Notre- Dame Cathedral of Paris, France. See those skeletal, rib-like arches coming off the cathedral? Those are the flying buttresses.

Flying buttresses of Notre Dame
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