Roofs are one of the most important parts of any building. They protect against harsh weather, keep energy costs down, and extend the life of the structure. But not all roofs are created equal. Over the years, roofing technology has improved, and one of the biggest breakthroughs was the Pittsburgh Double-Lock Seam.
This seam revolutionized metal roofing, making it stronger, more durable, and nearly leak-proof. One of the most famous roofing systems to use this technology is the MR-24 Roof System, introduced in 1969. With more than 2 billion square feet installed worldwide, it remains one of the best-performing roofs in the industry.
So, what makes the Pittsburgh Double-Lock Seam so special? And how did it change the roofing industry forever? Let’s explore its history, engineering, and why it continues to be the gold standard in roofing today.
The Birth of the Pittsburgh Double-Lock Seam
The double-lock seam was first developed for use in metalwork, where strong, sealed joints were necessary to keep materials secure. As metal roofing became more common, the Pittsburgh Double-Lock Seam was adapted to create weathertight, long-lasting roofs.
Unlike traditional roofing seams, which can come apart over time, the Pittsburgh seam uses a 360-degree mechanical lock to create a tight, monolithic surface. This means the seam is rolled twice during installation—the same type of seam you’d find on the top of a Coke can.
In the past, many roofs relied on single-lock seams or exposed fasteners, which could allow water to seep in. The Pittsburgh Double-Lock Seam changed that by making roofing systems much stronger, reducing leaks, and improving overall durability.
How the Pittsburgh Double-Lock Seam on the MR-24 Works
The strength of the Pittsburgh Double-Lock Seam comes from its 360-degree interlocking design, which is mechanically sealed in the field to create a continuous, weathertight roof. Here’s how it works:
- Roof panels are pre-punched in the factory for precise alignment and a snug fit.
- Factory Pre-Fold: The roof panels are pre-punched and initially folded to 90 degrees in the factory.
- First Field Seam: A seaming machine is used on-site to fold the seam an additional 90 degrees, bringing it to 180 degrees.
- Final Field Seam: The seaming machine makes another 180-degree fold, completing the full 360-degree Pittsburgh Double-Lock Seam
This double-lock process is so effective that it’s the same type of sealing method used in soda cans—which, as we know, don’t leak.
The MR-24 Roof System: Perfecting the Innovation
In 1969, the MR-24 Roof System was introduced as the first standing-seam metal roof to feature the Pittsburgh Double-Lock Seam. It set a new industry standard and remains the most specified metal roofing system today.
Here’s why the MR-24 Roof System stands out:
- Unmatched longevity – MR-24 roofs can last twice as long as conventional roofs, with documented lifespans of over 50 years.
- Factory-punched panels – Ensures perfect alignment and eliminates gaps that could cause leaks.
- Built to handle temperature changes – Roofs expand and contract daily. The MR-24 system uses floating clips that allow for movement, preventing stress on the seams.
- Tested for extreme weather – The MR-24 Roof System holds a UL Class 90 wind uplift rating and meets hurricane-zone requirements.
- Energy efficiency – Supports insulation up to R-40, reducing heating and cooling costs.
Proven Performance Over Time
The Pittsburgh Double-Lock Seam and the MR-24 Roof System have been tested and proven for over five decades. Here are a few examples of their real-world durability:
- Water tank test – When the MR-24 system was introduced, engineers built an 18×18-foot tank using Pittsburgh-seamed panels and filled it with 10 inches of water. After five months, there was no leaking or distortion.
- Wind resistance – The MR-24 system has survived some of the harshest storms and hurricanes, meeting ASTM and FM Global wind uplift standards.
- Energy savings – Building owners using MR-24 have reduced their energy costs thanks to its ability to hold high-performance insulation.
The Legacy of the Pittsburgh Double-Lock Seam in Modern Roofing
Today, the MR-24 with its Pittsburgh Double-Lock Seam is still the go-to choice for commercial and industrial metal roofs. The MR-24 Roof System continues to evolve, offering:
- Metal-over-metal re-roofing options, allowing old roofs to be upgraded without removal, saving money and reducing waste.
- Stronger seaming technology, making installation faster and even more reliable.
- New cool roof finishes, which reflect sunlight and help reduce energy costs.
Wrapping Up
The Pittsburgh Double-Lock Seam changed roofing forever by making metal roofs stronger, longer-lasting, and more resistant to leaks. The MR-24 Roof System took this technology to the next level. For building owners and contractors looking for the best roofing system on the market, the answer is clear: The Pittsburgh Double-Lock Seam and the MR-24 Roof System.
If you’re considering a new roof, reach out to us at MAR Building Solutions, Kansas City’s Butler Builder, to discuss a Butler roofing system for your building.
