Star Bolts: A Philadelphia Perspective

Star bolts are also known as structural ties. They are used for stabilizing masonry while adding aesthetic charm.

If you’ve ever strolled through the charming streets of Philadelphia, you might have noticed large, star-shaped metal plates adorning the brick facades of rowhomes and historic buildings. Most people assume they are just for aesthetic appeal. These are “star bolts”, also known as structural ties or anchor plates, and they’re far more than just decorative accents. In this blog post, we’ll dive into what star bolts are, why they’re so common in Philadelphia’s architecture, and how they address structural issues in buildings, particularly those constructed between the 1890s and 1930s.

What Are Star Bolts?

Star bolts are large, often star-shaped metal plates connected to long iron or steel rods, called tie rods, that run through a building’s masonry walls and anchor to internal wooden or steel joists. These rods and plates work together to stabilize brick or stone masonry walls, preventing them from bowing outward or collapsing. While their distinctive star shape adds a touch of aesthetic charm, their primary role is functional: to reinforce the structural integrity of older masonry buildings.

In Philadelphia, star bolts are a common sight on rowhomes and other brick structures, especially in historic neighborhoods like Brewerytown, South Philly, Fishtown, and Society Hill. Their prevalence is tied to the city’s architectural history, where many buildings from the 18th and 19th centuries—and even into the early 20th century—were constructed with load-bearing brick masonry and timber framing.

Why Are Star Bolts Used in Philadelphia?

Philadelphia’s architectural landscape is dominated by rowhomes, which were built extensively from the colonial era through the early 20th century. These homes typically feature brick masonry walls with wooden joists that span side-to-side, pocketed into party walls. While the joists brace the shared “party” walls between neighboring homes, the front and back walls of these structures are more vulnerable to movement, especially as they age.

During the 1890s to 1930s, many Philadelphia buildings were constructed with materials and techniques that, while innovative for the time, could lead to structural issues over decades and in many cases centuries. Star bolts became a go-to solution for stabilizing these aging structures, particularly when walls began to bow or buckle. They are a remarkably effective solution, and here’s why they’re so critical:

1. Aging Materials and Environmental Stress: The iron anchors originally used in many 19th- and early 20th-century buildings were prone to corrosion, especially when exposed to repeated wet-dry and freeze-thaw cycles in exterior masonry walls. Over time, this decay weakened the anchors, reducing their ability to brace walls. Star bolts, made of more durable materials like galvanized steel or ductile iron, are installed as replacements to restore stability.

2. Cost-Effective Repairs: Rebuilding an entire masonry wall is expensive and disruptive. Star bolts offer a more affordable alternative by securing bowing walls to the building’s internal framework, preventing further movement without the need for extensive reconstruction.

3. Preserving Historic Character: Philadelphia places a high value on its architectural heritage. Star bolts not only stabilize walls but also blend seamlessly with the city’s historic aesthetic. They add what a phenomenal real estate agent friend once termed “jewels” to the character of any structure. Their star-shaped design (although you may see a phlethora of other shapes) has become a celebrated feature, adding character while maintaining structural integrity.

   
   

Common Structural Failures Addressed by Star Bolts

Buildings constructed between the 1890s and 1930s in Philadelphia often face specific structural challenges due to their design and the materials used. Star bolts are commonly employed to address the following issues:

1. Bowing or Bulging Walls: One of the most frequent problems in older masonry buildings is the outward bowing of front or back walls. This occurs because these walls are only connected to the rest of the structure at their edges and roof, making them prone to buckling under their own weight or due to shifting foundations. Star bolts counteract this by tying the walls to the floor joists, distributing pressure evenly and preventing further movement.

2. Weakened Foundations: Unstable or settling foundations can cause walls to lean or crack. This was particularly common in Philadelphia rowhomes built in the early 20th century, where poor-quality lime mortar was sometimes used instead of more durable Portland cement. Star bolts help stabilize walls affected by foundation issues, preventing partial or complete collapse.

3. Lack of Adequate Bracing: Many buildings from this era lacked sufficient bracing for their front and back walls, especially those with wide window or door openings that weakened the facade. Star bolts provide the necessary reinforcement by anchoring walls to the internal structure, compensating for design flaws or insufficient load-bearing capacity by adding rigidity.

4. Damage from Adjacent Construction: In dense urban areas like Philadelphia, construction on neighboring properties could destabilize shared party walls or adjacent structures. For example, if an adjacent building was demolished or modified, it could cause a rowhome’s walls to lose support, leading to bowing. Star bolts are often installed to restore stability in these cases.

5. Aging Mortar and Brick Deterioration: The lime mortar used in many pre-1930s buildings could degrade over time, especially when exposed to moisture. This weakened the bond between bricks, making walls more susceptible to movement. Star bolts reinforce these walls, ensuring they remain secure even as mortar deteriorates.

   
   

How Star Bolts Are Installed

Installing star bolts is a precise process that requires expertise from structural engineers and skilled contractors. Here’s a simplified overview of the process:

1. Assessment: A structural engineer evaluates the extent of wall bowing or other issues, determining the number and placement of star bolts needed.

2. Permits and Preparation: Local permits are obtained, and interior areas (like drywall or electrical systems) are cleared where tie rods will penetrate.

3. Drilling and Installation: Pilot holes are drilled through the exterior brick wall and aligned with interior joists. Threaded steel tie rods are inserted, extending from the exterior wall through the joists. Star-shaped washers are placed on the exterior ends, and nuts are tightened on both sides to secure the rods and apply even tension, pulling the wall back toward the building’s framework.

4. Finishing Touches: The exterior star plates are fastened flush against the brick, and any interior or exterior repairs (like patching holes or repointing mortar) are completed to maintain the building’s appearance.

   
   

Why Star Bolts Matter in Philadelphia

Star bolts are more than just a practical fix—they’re a testament to Philadelphia’s commitment to preserving its architectural heritage. If you are like me, you feel a sense of continuity and nostalgia when you walk down a street with brick row homes. By addressing structural failures in a cost-effective and visually appealing way, they allow historic rowhomes to remain safe and functional for generations. Whether you’re a homeowner noticing signs of bowing walls (like sinking floors or doors that won’t close) or simply a fan of Philly’s unique architectural character, understanding the role of star bolts deepens your appreciation for the city’s built environment.

If you suspect your home needs star bolts or want to learn more about maintaining a historic property, give Axial Force Engineering a call to discuss your situation. We can help ensure your home remains both safe and beautiful.

Next time you walk through Philadelphia’s historic neighborhoods, take a moment to spot those star bolts—they’re not just stars; they’re the unsung heroes holding the city’s past together.