New Composite Slate Roof Tops Historic Denver Church

Soaring 90 feet tall, Saint John’s Cathedral would be intimidating to anyone — especially the team assigned to re-roof the massive structure. However, the experts at Horn Brothers Roofing jumped at the opportunity to install 245 squares of DaVinci Roofscapes composite slate tiles on one of Denver’s most historic buildings.

“Three main parts of the church were constructed in different eras with building methods and materials unique to those times,” says Mark McMillan with Horn Brothers Roofing. “Construction on the cathedral was completed in 1910. The Parish Hall was added in 1927 and then Roberts Hall in 1957.  We had to find a way to remove and safely lower down tons of existing real slate and clay tile roofing materials before we could begin installation of the new DaVinci Roofscapes Single-Width composite slate tiles.”

Protect Historic Church

Before the replacement work got started, McMillan and representatives of the church were challenged to gain approval from the Denver Landmark Preservation Commission.

“This is definitely an older structure and officials involved in historical renewal in Denver wanted the project done right,” says McMillan. “We took time to fully examine the entire facility and make product recommendations.

“When we inspected the cathedral, the only roof access involved climbing an old wooden 90-foot ladder originally installed in 1910. Once we reached the top of the bell tower, we had to balance on a coffee can. We steadied ourselves on the bell yoke and then squeezed through a two-foot by two-foot vent opening. That was quite a challenge!”

Other challenges of the project included the protection of massive stained glass windows in the sanctuary. Over a century old, the stained glass windows, which encompass all four sides of the sanctuary, are valued at more than $14 million.

Adding to the complexity of the job, a new $3 million pipe organ had been installed just weeks prior to the re-roofing project. The Horn Brothers Roofing team had to make sure that the windows were protected and that century-old dust didn’t drift from the ceiling into the new copper organ pipes during the re-roofing.

Safety First

After removing the old hail-damaged natural slate roofing materials, the roofers started installing the composite slate products. Thirty-nine squares of DaVinci Single-Width Slate in a Slate Gray color were installed on the Cathedral. For the Parish Hall, 55 squares of the product were installed in a Canyon color blend. And, for the gabled roof on Robert’s Hall, 151 squares of the Single-Width composite slate product in the European blend were installed.

horn brothers roofing composite slate   horn brothers roofing composite slate

“Throughout this entire project — which took a total of 18,000 man hours — safety was our top consideration,” says McMillan. “We had a safety manager on site at all times and took extra precautions to ensure the security of our crew and people on the ground.”

Due to the height of the cathedral, along with high wind concerns, a 126-foot tall lift was brought on site for off loading existing tiles, on loading new materials and manpower. The precision and mobility of the lift ensured the safety of the property, the public and onsite crews.

The lift was used to off load 103 squares of brittle, heavy slate in a lift bucket. The weight of the natural slate turned this into a very time consuming process.

horn brothers roofing composite slate

As the project moved to different locations, each area — including sidewalks, the school zone, parking lots and entry ways to the church — were secured and monitored. Due to the very close proximity of schools to the church extra precautions were in place in the mornings and when school let out.

“With the height of the cathedral and the 18 on 12 pitched roof on Robert’s Hall and Parish Hall, the crews’ safety was a major concern,” says McMillan. “Our employees were tied off at all times for both fall protection and to traverse the different building slopes. On the ground we had team members taking extra precautions to make sure that pedestrians stayed a safe distance away from the work areas.”

The Challenges Continue

horn brothers roofing composite slateAccording to McMillan, perhaps the most challenging aspect of re-roofing the cathedral was the apse. Because of its semi-circular shape, each piece of insulation and nail base had to be cut in precise shapes and beveled at multiple angles to replicate the historical architecture.

“Every structure in this project had its own unique set of challenges,” says McMillan. “As we moved to Robert’s Hall, failing copper nails had allowed the heavy slate to detach and fall to the ground. The remaining old slate shingles had to be individually hand-removed.

“We consulted with an engineering firm to determine that the existing gypsum under the slate needed to be covered with OSB to provide a suitable nailing surface for the DaVinci tile. We decided that a toggle bolt system was the best option. This meant we had to assemble 3,864 toggle bolts and then pre-drill the installed OSB with ¾-inch holes. 70 drill bits were worn out during this phase.”

While weather and mechanical issues with the lift caused additional challenges, the Horn Brothers team was able to complete the entire job, including the installation of composite slate, in just over four months.

New Roof Protects Historic Church

Now securely installed, the new composite slate roof has eliminated worries of falling old slate tiles while adding more beauty to the church exterior. While parishioners are pleased with the look of the new roof, they’re waiting for severe weather to prove their investment was a wise one.

“We’re happy to have this roof overhead, but we’re really waiting for a few years and some bad storms to hit to truly see how the impact-resistant roof holds up,” says Judy Allison, who served as director of facilities at Saint John’s Cathedral during the re-roofing process. “This was a very large project for us. We first had to gain approval from several groups within the church and then from the Denver Landmark Preservation Commission.

“Our church has made an investment in this composite slate roof. The beauty and aesthetics of the DaVinci roof are wonderful. We’ll be especially happy with the roof when we see how it performs over the years.”

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