The Secret Life of Buildings: Star Bolts


November 21, 2018 Tags:

On a stroll through the streets of Philadelphia, you’ll likely spot star bolts somewhere along the way. In a city so rich with colonial history, these bolts could easily be mistaken for decoration. And while they certainly add a charming element to these brick homes, they’re actually working hard to keep the front walls of these houses upright.

Brick Rowhome painted tan with cream colored star bolts and green door

Why Are Star Bolts Needed?

To understand why star bolts are sometimes needed in older homes, we’ll explore the basics of rowhome construction. Rowhomes are built by connecting wooden joists between the side walls (also known as party walls). The front and back of a rowhome are only connected at the edges of these side walls, not directly to the strong wooden joists. Over time, this connection can weaken, and the exterior walls gradually separate from the house, resulting in exterior walls which bulge outward. This can happen due to foundation problems, as well as problems with the bricks themselves.

Brick homes built before 1920 were crafted using lime mortar. Unlike modern mortar, (made using portland cement), lime mortar gradually dissolves when exposed to the elements. Disintegrating mortar is one reason that the facades of rowhomes can weaken and begin to separate from the house.

White Brick Rowhome Philadelphia with green lintels and steel starbolts for structural support

When installing star bolts, a mason will remove the lime mortar and repoint the brick with modern mortar. The mason will also create a connection between the exterior of the house and the floor and ceiling joists. The severity of the bulging wall will determine how many joists the mason will need to connect to the star bolt. This is why star bolts are visible along the floorline of the house.

Star bolts are a fairly inexpensive solution to a fairly common problem in older brick homes. At Solo, we’re proud to live in a city so rich with architectural history. Whenever we see star bolts, we’re glad the owners of these homes took the time to properly care for a restore their aging homes. Hopefully, these rowhomes can continue to be lived in and loved for generations to come.

Check out this video below to see an animation that visualizes how star bolts work, and why they’re necessary for many old rowhomes in Philadelphia:

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