A Slate Roofer Shares Slate’s History in and Benefits for the Carolinas

Although slate had been used as ballast for ships crossing the Atlantic as early as the mid-1600s, its use was somewhat sparse in the Carolinas until after the great fire. With the Civil War in full bloom, a catastrophic fire broke out in Charleston in 1861, and the city was decimated. However, the Great Reconstruction Era (1865-77) brought shiploads of slate and bricks from North Wales. Welsh slate from the Penrhyn quarries and bricks and tiles from Flintshire and Chester made their way to nearby Liverpool, England, and ultimately to the historic Battery of Charleston.

Not to be outdone, the American quarries started to ship to the Carolinas also. New quarries opened up all along the New York and Vermont corridor, and, in the South, the Virginia Buckingham Co. started quarrying slate in 1867. Slate roofing was growing exponentially at this time, and the Carolinas were consuming it at a very rapid rate.

This dormer features Vermont Black installed in a German style.

This dormer features Vermont Black installed in a German style.

As a large port city, Charleston was able to acquire a wealth of different types of slate for its roofs: purple and gray slates from Penrhyn, Wales; Pennsylvania black slates; lustrous black Buckingham slates from Virginia; and greens, purples and reds from Vermont. Although it took more than a decade, Charleston was rebuilt in a grand manner with beautiful slate roofs as far as the eye could see.

Unfortunately, in 1989 Hurricane Hugo struck Charleston, causing nearly $6 billion in damage. The silver lining was many of these historic properties with slate roofs were 100 to 200 years old by 1989 and were in need of major restoration. From 1989-91, Charleston experienced a huge building boom with the insurance companies footing the bill for the restoration of the city. Tradespeople skilled in historic restoration were called in from all over the country and world. Among them were slate roofers hired to assess and restore the city’s slate roofs.

Learning Experience

Having only been a slate roofer for four years at the time, Charleston proved to be a great learning experience for me. Often working 12- to 15-hour days to keep up with the workload, I was able to personally observe various slating techniques from more than a century ago.

For example, still one of the most unique slate roofs I’ve encountered in my 20-plus years in slate roofing, was on a private residence on King Street. It had sustained minimal damage, and in the process of our repairs, we could see why. The entire slate roof was laid in a bed of mortar with wooden pegs where one usually finds nails. Needless to say, it was quite an adventure to restore it back to its prominence.

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Rooftop Equipment Mounting and Penetrations for Low-slope Standing-seam Metal Roofs

Standing-seam metal roofing offers a durable, sustainable alternative to other roof types and can provide maintenance-free service for five to 10 decades. Sadly, this exceptional lifespan often is sabotaged with the mounting of essential rooftop equipment and ancillary mechanicals.

Metal roofing can make use of special seam-clamping hardware that grips the standing seam without puncturing the membrane. Seam clamps have made metal roofing a preferred roof type for mounting photovoltaic solar arrays. PHOTO: Metal Roof Advisory Group Ltd.

Metal roofing can make use of special seam-clamping hardware that grips the standing seam without puncturing the membrane. Seam clamps have made metal roofing a preferred roof type for mounting photovoltaic solar arrays.

Regardless of the roof type involved, consultants generally agree that the best way to prevent roof-related problems is to clear the rooftop of everything possible and just let it function as a roof—not a mechanical equipment platform. However, such a perfect roof continues to elude us, as it becomes necessary or convenient to mount HVAC equipment, screens to hide it, piping to fuel it, scuttles to access it and walkways to service it. The list of rooftop mountings also may include plumbing vents, satellite dishes, lightning protection, snow retention systems, solar collectors, advertising signage and fall-protection systems to maintain all the foregoing. To help achieve relatively trouble-free roofs, this segment provides some basic understanding of the dos and don’ts in situations where rooftop equipment mounting is requisite.

Penetration-free Attachment

A good “first rule” about any rooftop mounting is to avoid penetrating the membrane whenever possible. While this may seem obvious, the tenet is often violated with standing-seam metal. The norm for attaching things seems to involve anchoring the item to the structure through the roof. When this happens, it not only threatens weather integrity, but can also violate the membrane’s thermal-cycling behavior by inadvertently pinning the panel to the structure. Such a point of attachment will fatigue and fail from forces of thermal expansion within a short time. Fortunately, scores of items and equipment can be securely mounted to metal rooftops without any penetration whatsoever, actually making metal roofing more user-friendly than other roof types.

In terms of mounting ancillaries, metal roofing can use special seam-clamping hardware that grips the standing seam without puncturing the membrane. Unlike many other types of roofing, metal is a rigid, high-tensile material. The seam area creates a beam-like structure that can provide convenient anchorage for walkways, solar arrays, condensing units and gas piping without harming the roof’s weathering characteristics. Mechanicals can be safely and cost-effectively secured to these seam clamps, leaving the roof membrane penetration free. Seam clamps can provide holding strength of up to several thousand pounds on some profiles and gauges, last the life of the roof and preserve thermal-cycling characteristics. Using seam clamps when possible for ancillary mounting will eliminate unwanted holes and other potential problems.

Seam clamps allow even cumbersome ancillary items to be attached to metal roofs without penetrating the rooftop. PHOTO: Metal Roof Advisory Group Ltd.

Seam clamps allow even cumbersome ancillary items to be attached to metal roofs without penetrating the rooftop.

Clamps should be made only of noncorrosive metals—typically, aluminum with stainless-steel mounting hardware. These metals are compatible with virtually anything found on a metal roof, except copper (with which there are dissimilar metallurgy issues). Dissimilar metals in electrolytic contact will induce galvanic corrosion of the less noble metal. In cases involving copper roofing, brass clamps should be used with stainless-steel hardware.

Seam clamps generally integrate with the profile and seam folding, and in some way “pinch” the seam material to anchor them in place. Preferred methods of doing this involve setscrews tightened against the seam causing a detent in the seam material that in turn creates a mechanical interlock of the setscrew, seam and clamp, providing the greatest holding strength and durability. Setscrews should have round, polished points to prevent galling metallic coatings, which can lead to corrosion. In like fashion, and regardless of the method of engagement, any clamp device should avoid any sharp points or nodes that could potentially pierce or gall metallic coatings of steel or cause fatigue and fracture points of other metals.

It also is important to remember that any loads introduced into the clamp will be transferred to the panels and their anchorage to the structure. Consequently, anchorage must be capable of withstanding the added load. The best practice is to utilize clamps that have been appropriately tested for material and seam-specific holding strength; be sure in-service load does not exceed that of the published holding strength, including factors of safety. The roof manufacturer should also be consulted with respect to approval of devices used.

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