Historic Slate Roof Restorations

Creative assistance and innovation in slate roof and re-roof installations for residences, churches, and other historical buildings

Since 1955, the Greenstone Slate Company has worked with architects, general contractors and property owners in restoration projects to match color, texture and other features in slate roof restoration projects including matching new construction aesthetics to the surrounding buildings of a historic property. More recently, this has come to include assisting with retaining or adding a slate roof where there are structural support challenges. The ability to reduce the weight of a slate roof through the inclusion of contemporary roofing materials that reduces the amount of slate needed has made the difference for many projects.

It is well accepted that a genuine slate roof will stand the test of time, and there is an abundance of other benefits: aesthetics, increased property value, and durability including the withstanding of hurricane force wind and rain, its excellent impact resistance from hail, its stability in temperature extremes, and of course slate is fireproof. With so many reasons to choose slate why are we seeing the removal of slate roofs during the restoration of residences, churches and other historic buildings? The usual answer is the weight of slate.

Traditional slate installation techniques are not always possible in historic restoration

One of the main reasons a slate roof would be removed from historic buildings is due to concern for the building’s structural integrity. A natural slate roof installed with 1/4” slate and using traditional installation methods, has an average weight of 9 pounds per square foot. As the buildings age, the structural support ages as well and may no longer be able to mechanically withstand the weight of a traditional installation. While one of the primary benefits of slate is, in fact, its density—offering protection that no other roofing material can—roofing professionals have often looked to alternative roofing materials that were lighter weight but not necessarily as strong and long-lasting as natural stone. But a slate roof’s weight no longer has to be a constraining issue.

SlateTec and Nu-lok logos

Methods for reducing roof weight by up to 40%

Greenstone Slate® provides two installation methods for installing a natural slate roof with reduced weight. These approaches can be used for most building restorations including those that did not previously have a slate roof. Both can reduce roof weight to under 6 pounds per square foot with standard grade slate (1/4” to 1/2”). The SlateTec™ installation system uses an interlayment applied to each course that reduces slate headlap which in turn reduces the total amount of slate needed—usually by about 40%. The Nu-lok installation system places slate on a grid and reduces headlap with galvalume link channels that guide water downward and support the slates on all sides making the roof walkable. The grid system creates ventilation space under the slate and provides the option of flush-integrated solar panels. Like SlateTec, Nu-lok reduces roof weight by about 40%.

Are there compromises with lightweight installation methods?

With SlateTec, traditional slate roof aesthetics are maintained

In keeping with the classic aesthetics of historic slate roofs, SlateTec’s appearance will be identical to that of a traditional slate roof. The innovative SlateTec system can be used with all the same slate grades as a traditional installation retaining the visual character and architectural details. All traditional slate roof design options are available including unequal slate lengths, random widths, graduated installations, drop downs, and staggers, as well as all Vermont slate colors, blends and grades.

Nu-lok exchanges some traditional slate roof aesthetics for benefits not possible with other installation methods

The Nu-lok system includes a grid that supports the slates uniformly making the roof walkable. The grid also provides an air gap between the slate and the deck that ventilates under the slate, that reduces heat entering the building which in turn reduces HVAC operating costs. While any Vermont slate color, or a blend of colors, can be installed using the Nu-lok installation system, the grid design precludes traditional details such as variable slate lengths and graduated courses. However, Nu-lok is an ideal solution for roof projects where a natural slate is desired and there is an interest in solar panels. Nu-lok solar panels integrate flush with the slate and is a very elegant solar solution. In addition, the ease of individual slate removal makes repairs simple and the access to the roof deck for wiring, or other building service needs is simply unprecedented.

Time-tested techniques

SlateTec installs in a traditional fashion using (preferably) copper nails to secure the slates—exactly like the traditional slate installation method. SlateTec has simply advanced the installation process by using its patented, easy-to-install interlayment. The Nu-lok™ Roofing System has been installed on thousands of roofs worldwide since its introduction in the 1980s. It uses hardware that is consistent with the anticipated lifespan of a slate roof including galvanized steel battens, galvalume link channels and stainless steel securing hooks.

Durability and protection

Both SlateTec and Nu-lok slate roofs provide excellent protection from extreme weather. They meet or exceed requirements for withstanding hurricane wind and rain, hail resistance, and are fireproof. SlateTec’s tough, interlayment works with the natural slate to protect the roof and is the key to removing the burden of the extra weight as it allows for less slate headlap. But less slate, doesn’t mean that this slate roof is any less durable or long-lasting than those installed using traditional installation methods. Actually, SlateTec interlayment enhances building protection by continuing to protect the building from water damage should a slate be broken or lost while still providing Class 3 impact (hail) resistance. Both the Greenstone Vermont slate and the SlateTec interlayment carry a 100-year warranty—testimony to its quality and longevity. Greenstone slate install with the Nu-lok installation system has been tested and is Miami-Dade approved for installation in hurricane zones. The Nu-lok installation materials combined with the natural slate tiles are an important feature to consider especially for buildings in areas where wild fires are common.

Easy installation and maintenance

Any professional roofing contractor can install a slate roof using either the SlateTec method or the Nu-lok installation system although you may want to consider a contractor that specializes in historic property preservation when working with historic properties. A properly installed slate roof requires little maintenance over the life of the roof. However, occasionally individual slates are damaged. Both the SlateTec and Nu-lok processes allow for individual damaged slates to be replaced.

Genuine slate roofs for new or re-roof projects

Genuine slate roofs can now be installed on nearly any new or re-roof project, even historical roof restorations that may now have structural obstacles and a certain aesthetic is desirable to maintain. Utilizing today’s advanced technologies and the highest quality roofing materials, a genuine slate roof can continue to distinguish itself as the longest lasting and arguably one of the most beautiful available, and practical in a much wider range of projects.

For more information

To discuss this article or for more information about Greenstone Slate or the reduced weight slate roof installation system, call 800.619.4333 or contact us here.

The Greenstone Slate Company is ready to assist with any historic slate roof restoration project—from selecting slate colors and advising on methods of slate installation to helping a property owner find a contractor that specializes in historic property preservation.

Call us at 800 619 4333 or click here to contact us.

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