Project Profiles: Historic Preservation

CATHEDRAL OF ST. PAUL, BIRMINGHAM, ALA.

Team

ROOFING CONTRACTOR: Midland Engineering Co., South
Bend, Ind.
ARCHITECT: ArchitectureWorks LLP, Birmingham
GENERAL CONTRACTOR: Hoar Construction LLC, Birmingham,
MASONRY CONTRACTOR: Ziolkowski Construction Inc., South Bend

The cathedral’s intricate slate tile patterns incorporated three slate colors and square and deep bevel cut tiles.

The cathedral’s intricate slate tile patterns incorporated three slate colors and square and deep bevel cut tiles.

Roof Materials

The Catholic Archdiocese of Birmingham required the cathedral’s new roof system be a historically accurate reproduction of the original in materials, design and craftsmanship. The cathedral’s intricate slate tile patterns incorporated three slate colors and square and deep bevel cut tiles. Six large slate crosses and multiple accent patterns, barely visible on the faded original roof, required exacting measurements prior to tear-off and a high level of precision to recreate and maintain over such a large field and on octagonal steeples.

Because of metal thinning brought on by their advanced age, every copper architectural and functional feature in the existing roof system had to be carefully removed and shipped to Midland Engineering’s South Bend facility to be historically replicated in its metal shop. This included seven ornate crosses (up to 17-feet tall), finials, turret caps and more. There were more than four dozen components, for which no original prints existed, as well as over 500 feet each of custom copper cornices and radius gutters with matching straps. More than 20,000 square feet of 16- and 20-ounce copper was utilized for fabrication of architectural elements and flashing.

Midland Engineering was asked to make improvements to the original roof system to improve attic ventilation while maintaining the Gothic Revival period look. To accomplish this, the crew integrated bronze screen (invisible from the ground) into the original copper cornice and eave design to provide improved cold air intake while new louvered copper dormers replaced the original painted roof ventilator.

An updated lightning protection system was incorporated into the new roof design, hidden within many of the new copper crosses and other architectural elements. The system was fabricated in Midland Engineering’s shop to maintain the Gothic Revival look.

The metal shop also clad 10 previously painted windows and mullions in copper, effectively eliminating frequent and costly maintenance. These windows, reachable only by crane at considerable expense, formerly required painting and other maintenance every five to seven years.

About 6,500 square feet of lead-coated copper, which patinas to a limestone color, was utilized to cap all limestone exposed to weather, reducing ongoing maintenance of limestone joints.

Extensive termite damage to structural framing required repair prior to installation of the new roofing system. Upon removal of the original slate roof and completion of the structural repairs, the new roof was dried-in and installation of the new slate roof began. The historically accurate replacements of the original copper architectural features were installed according to schedule.

SLATE SUPPLIER: North Country Slate
COPPER SUPPLIER: Hussey Copper

Roof Report

The Cathedral of St. Paul is the centerpiece of the Roman Catholic Diocese of Birmingham. Completed in 1893 at a cost of $90,000, the cathedral is widely considered to be a handsome example of the American Neo-Gothic variant of the Gothic Revival style. The cathedral measures 96-feet wide by 140-feet long and encompasses more than 60,000 square feet. It features twin octagonal steeples, rising 183-feet high.

Work schedules on this project were a challenge. The contract required parishioner and clergy access to the church must be maintained 24 hours a day, seven days a week, throughout the eight-month duration of the project. Further, because of the noise inherent in roof construction, work schedules had to be planned around regular church services and events and rescheduled several times a month for funerals and other unscheduled events.

“We could not have been more pleased with the work accomplished by the team from Midland Engineering,” says Very Rev. Kevin M. Bazzel, V.G., J.C.L., rector of the Cathedral of St. Paul. “It is a marvel to us to be able to see the church in its original glory, and all of this thanks to Midland!”

The National Roofing Contractors Association, Rosemont, Ill., awarded Midland Engineering the prestigious Gold Circle Award in 2016. Midland was recognized in the Outstanding Workmanship—Steep-slope Category.

Photo: Rob Culpepper

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Attention Roof System Designers: Numerous Roof Components Work Together to Affect a Building

There has been a great deal of opinion expressed in the past 15 years related to the roof cover(s), or the top surface of a roof system, such as “it can save you energy” and “it will reduce urban heat islands”. These opinions consequently have resulted in standards and code revisions that have had an extraordinary effect on the roofing industry.

The building type should influence the type of roof system designed. Some spaces, like this steel plant, are unconditioned, so insulation in the roof system is not desired.

The building type should influence the type of roof system designed. Some spaces, like this steel plant, are unconditioned, so insulation in the roof system is not desired.

Let’s say it loud and clear, “A single component, does not a roof make!”. Roofs are systems, composed of numerous components that work and interact together to affect the building in question. Regardless of your concern or goal—energy performance, urban heat-island minimization, long-term service life (in my opinion, the essence of sustainability) or protection from the elements—the performance is the result of an assembled set of roof system components.

Roof System Components

Energy conservation is an often-discussed potential of roofs, but many seem to think it is the result of only the roof-cover color. I think not. Energy performance is the result of many factors, including but not limited to:

Building use: Is the building an office, school, hospital, warehouse, fabrication facility, etc.? Each type of building use places different requirements on the roof system.

Spatial use and function be low the roof deck: It is not uncommon in urban areas to have mechanical rooms or interstitial spaces below the roof—spaces that require little to no heating or cooling. These spaces are typically unconditioned and unoccupied and receive no material benefit from the roof system in regard to energy savings.

Roof-deck type: The type of roof deck—whether steel; cast-in-place, precast and post-tensioned concrete; gypsum; cementitious wood fiber; or (don’t kill the messenger) plywood, which is a West Coast anomaly—affects air and moisture transport toward the exterior, as well as the type of roof system.

Roof-to-wall transition(s): The transition of the roofing to walls often results in unresolved design issues, as well as cavities that allow moisture and vapor transport.

Meanwhile others, like this indoor pool, require extreme care in design and should include a vapor retarder and insulation.

Meanwhile others, like this indoor pool, require extreme care in design and
should include a vapor retarder and insulation.

Roof air and/or vapor barrier: Its integration into the wall air barrier is very important. Failure to tie the two together creates a breach in the barrier.

Substrate board: Steel roof decks often require a substrate board to support the air and vapor barrier membranes. The substrate board also can be the first layer of the roof system to provide wind-uplift resistance.

Insulation type: Each insulation type—whether polyisocyanurate, expanded polystyrene, extruded polystyrene, wood fiber, foam glass or mineral wool—has differing R-values, some of which drop with time. Many insulation types have differing facer options and densities.

The number of insulation layers: This is very important! A single layer of insulation results in a high level of energy loss; 7 percent is the industry standard. When installing multiple layers of insulation, the joints should be offset from layer to layer to avoid vapor movement and thermal shorts.

Sealing: Voids between rooftop penetrations, adjacent board and the roof-edge perimeters can create large avenues for heat loss.

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