What is a miter? What is a mitered window?

The Geometry of Creating Corner Joints

Frank Lloyd Wright mitered glass, Wyoming Valley School (1957), Spring Green, Wisconsin.
Photo © Thompson Photography

The term mitered describes the process of joining together two pieces of wood, glass, or other construction material. Mitered corners are fitted together from parts cut at angles. Two pieces cut at 45 degree angles fit together to form a snug, 90 degree corner.

Definition of Miter Joint:

"A joint between two members at an angle to each other; each member is cut at an angle equal to half the angle of the junction; usually the members are at right angles to each other."—Dictionary of Architecture and Construction, Cyril M. Harris, ed., McGraw-Hill, 1975, p. 318

Butt Joint or Mitered Joint?

A mitered joint involves taking the two ends you want to join and cutting them at complementary angles, so they fit together and add up to the 90° of a corner. For wood, the cutting is usually done with a miter box and saw, a table saw, or a compound miter saw.

A butt joint is easier. Without cutting, the ends you want to join are simply attached at right angles. Simple boxes are often made this way, where you can see the end grain of one of the members. Structurally, butt joints are weaker than mitered joints.

Where does the word come from?

The origin of the word "miter" (or mitre) is from the Latin mitra for headband or tie. The ornamental, pointy hat worn by the Pope or other clergyman is also called a miter. A miter (pronounced MY-tur) is a way of joining things—even cloth—to make a new, strong design. Even in quilting, It's Easy to Sew Mitered Quilt Binding.

Examples of Mitering in Architecture:

  • Woodworking: The mitered butt joint is a basic in joining wood and may be the most common use of mitering. Picture frames are often mitered.
  • Interior Finishing: Look at the baseboard or ceiling trim in your home. Chances are you'll find a mitered corner.
  • Arches: Two stone blocks can be put together diagonally to form a miter arch, also called a pediment arch, with the joint at the peak of the arch.
  • Masonry: A closer—the last brick, stone, or tile in a row—may be a mitered closer, cut at an angle to form the corner..
  • Corner glass windows: American architect Frank Lloyd Wright (1867-1959) had the idea that if you could miter wood, stone, and cloth, why couldn't you miter glass? He convinced a construction team to try it, and it worked. The windows of the Zimmerman house (1950) have mitered glass corners that allow unobstructed views of the gardens. The 1957 Wright-designed Wyoming Valley School (shown here) in Wisconsin also has mitered plate glass corner windows.

The Frank Lloyd Wright Building Conservancy has an interesting Wright Chat on Mitered Windows on their website.

Frank Lloyd Wright and the Use of Glass:

In 1908, Frank Lloyd Wright was considering the modern notion of building with glass. "The windows usually are provided with characteristic straight line patterns," he wrote. It is the "cunning" arrangement of this geometry that becomes design. "The aim is that the designs shall make the best of the technical contrivances that produce them."

By 1928, Wright was writing about "Crystal Cities" made of glass. "Perhaps the greatest eventual difference between ancient and modern buildings will eventually be due to our modern machine-made glass," wrote Wright.

"Had the ancients been able to enclose interior space with the facility we enjoy because of glass, I suppose the history of architecture would have been radically different...."

The rest of his life, Wright envisioned ways he could combine glass, steel, and masonry—the building blocks of modernism—into new, open designs. "Popular demand for visibility makes walls and even posts an intrusion in almost any building to be got rid of at any cost in many cases."

The mitered corner window was one of Wright's solutions to advance visibility, indoor-outdoor connections, and organic architecture. Wright played at the intersection of design and construction methods, and he is remembered for it. The mitered glass window has become an icon of modernism—expensive and rarely used today, but iconic nonetheless.

Learn More:

  • Wood Joinery Types
  • How to Close an Open Mitered Corner
  • Tips for Buying a Power Miter Saw
  • How to Use a Compound Miter Saw
  • Make Your Own Mitre Box Soap Mold
  • Woodworking Projects Using a Miter Saw

Source: "Frank Lloyd Wright On Architecture: Selected Writings (1894-1940)," Frederick Gutheim, ed., Grosset's Universal Library, 1941, pp. 40, 122-123