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The Importance of the Keystone in Stone Arches

Sep 06, 2023

If you’re looking for ways to improve the look of your home’s exterior—specifically your home’s entrance—then you can’t go wrong with a stone arch. A stone arch provides a grand feeling to your entrance and draws the eye immediately, strengthening your entrance as the focal point of your home’s exterior. When it comes to the construction of a stone arch, you can’t dismiss the importance of the keystone. If you’re not familiar with how stone arches are built or why a keystone is so important, this article is for you.

building a stone arch
Traditional Patio by Atlanta Interior Designers & Decorators Yvonne McFadden LLC via Houzz

How Are Stone Arches Built?

Stone arches are created using a technique called “voussoir construction”, which involves stacking several wedge-shaped stones, called voussoirs, to create a curved arch. First the builder must create a solid foundation or support structure. This is commonly done with concrete or brick. Then, a temporary wooden or metal centering frame is made to support the arch while it’s being constructed. The stones are each cut with precision and stacked with adhesive according to the desired size and span of the final arch. Finally, the keystone is inserted at the top of the arch and the centering is removed to reveal the final product.

What Is the Keystone in an Arch Structure?

You’ve likely heard the word “keystone” used figuratively before to refer to the most important part of something, such as a keystone species or keystone states. This is because the keystone, also known as a capstone, is the most vital piece of stone arches. It’s the wedge-shaped piece that is located at the very apex of the arch.

Because the keystone takes a central position at the top of the stone arch, designers have often provided the keystone with a stylistic flourish in order to make it stand out from the rest of the voussoirs. This has been done throughout history. Some of the more basic examples include making the keystone a little larger than the rest of the voussoirs or using a knob or protrusion of wood or stone, known as a boss, in order to embellish the piece.

What Is the Importance of a Keystone in an Arch?

The keystone is the last piece put into place during the construction of the stone arch, locking all the other pieces into place and allowing the arch to bear the combined weight of the stones. Because the keystone is located at the top of the arch, it experiences the least amount of stress out of any of the voussoirs, yet it’s also the stone piece that the arch depends on in order to be self-supporting.

What Happens If You Remove the Keystone From an Arch?

Because the keystone plays an integral role in the construction of stone arches, removing the stone would challenge the integrity of the structure and cause the arch to collapse.

Stone Siding & Accents in Kansas City & Surrounding Areas

If you’re reading about the importance of keystones in stone arches because you’re interested in having stone siding or accents installed at your home, you’re in the right place. Johnson County Siding & Window Co. is the top source for stone accents in the Kansas City metropolitan area. Our stone supplier offers two types of keystones for stone arches, a chiseled face keystone and a slate face keystone. Contact us today to learn more.


If you know you want to get your home exterior project done, but are feeling stress about paying for it all at once, we can help.

Our financing partner, GreenSky, has sensible payment plans that work for homeowners who prefer to pay in installments. You can also ask your JoCo Siding & Window Co. sales representative about the details!

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