Thursday, March 7, 2013

Appropriate Roofing Material Choices for Historic Structures

The Old Conant Tavern in Townsend, MA, an historic New England easement property, receives a new cedar shingle roof. All photos: courtesy of the authorSelecting a historically appropriate roofing material is often restrictive as a simple matter of economy. Not everyone can afford a new slate roof. But individually landmarked structures and those in local historic districts are often monitored by historic district commissions (HDCs) that often require property owners to replace in-kind or with an otherwise historically appropriate material.  While the preference is typically “replacement in kind,” an intelligent argument for an alternative can often be made.  The HDC can consider other materials that were available at the time of construction, as well as what buildings of similar style in the community have on their roofs. A Queen Anne may have started with a polychromatic Vermont slate roof, but the commission can consider that nearby Queen Annes have monochromatic Monson slate or even cedar shingles. A Greek Revival may have a silver-coated tin roof, but few would argue with a homeowner willing to replace with copper standing seam. This blog article will look at several American building styles and the materials used to roof them.
 
Colonial Styles, 1620 to 1780

From the New England Salt Box to the Dutch vernacular homes of upstate New York, the earliest structures in the American colonies were roofed with wood shingles. It is a myth that they were covered with hand-split shakes, because these do not hold up well, rotting and failing in just a few years; ask anyone who has made the mistake of using them. Wood shingles were easily made by planing down the shakes to a uniform thickness for ease of installation.  In the Northeast, Eastern White Cedar was the typical material used, while cypress was often used in the South. Western Red Cedar was not used much in the eastern U.S. until after the 1850s and should not be considered appropriate on a circa-1820, Federal-style structure in Connecticut. Eastern White Cedar, however, rarely lasts longer than ten years in a roofing application. Instead, preservation architects now specify Alaskan Yellow Cedar. Predominantly distributed from British Columbia, this dense wood is favored because of its longevity and because it develops a silvery patina, like Eastern White, within one year.

Federal and Neoclassical Styles, 1780 to 1820
 
Many of these buildings have low-sloped roofs and are often obstructed by a balustrade that runs across the top of the eaves. In congested, urban environments the roof may not even be visible from the street. This raises the obvious question: What needs to be done when an element of the exterior is not within the street view? Most HDCs use that standard question to limit their purview over a proposed alteration.   The balustrade adorning the Federal-style St. Botolph Club’s roof in Boston’s Back Bay conceals the low-sloped roofing from view.If your roof falls into this category, then you should pick the most enduring and sustainable material you can afford. These structures were not often originally covered in slate, although many are today. Original roofs were wooden shingles, less than ideal on a roof with a shallow pitch. In some limited instances, standing-seam or flat-lock seamed roofs are seen on these building styles. To find out what’s appropriate, check out roofs on structures of the same style in your neighborhood and neighboring communities.

Greek Revival, 1820 to 1850

This style also features a low-sloped roof, typically 4:12. While the original roof material may have been wooden shingles, many in the Northeast were long ago replaced by a more sustainable material. Flat-lock tin or terne-coated steel were typical from the late 1800s on. Many have standing-seam roofing, although this system tends to be less conducive to the many and varied changes in the roof plane that multiple roofs and additions create.  A new copper roof and built-in gutters on a Greek Revival in historic Waterford, NY.Because many of these structures also have box gutters at the eaves, keep in mind that re-lining these systems is costly and will need to tie in to the new roof material. It is not uncommon for an affordable membrane (like EPDM or TPO) to be used on the majority of the roof and a costlier, appropriate material (like copper) to cover the visible, projecting “porch” roof

Gothic Revival, 1840 to 1860

While many of these structures were initially covered with wooden shingles, many had decorative styles and patterns. This was also a popular style when the slate industry in Vermont, Pennsylvania and Virginia started to produce roofing slate in such quantities that it could be realistically specified as a material choice. The influence of architect Frank Furness and others shone through, as polychromatic slate patterns adorned the Gothic “cottages” of Alexander Jackson Davis, Andrew Jackson Downing and their many disciples. In the South and in the Mid-Atlantic states, standing-seam roofing is quite common. Again, check out roofs on buildings of the same style in your neighborhood and neighboring communities. What’s appropriate?

Italianate, 1845 to 1875

While many Italianates have out-of-sight, low-sloped roofs that an HDC will not be concerned about, many of the “villa” variety have gables and other roof planes that are visible from the street. Like those on Greek Revivals, these roofs were often clad in flat-lock seamed or standing-seam sheet metal. In later years, many were re-roofed with clay tiles. Note that the advent of this new material correlates with the growth of the Ludowici firm in Chicago in the 1880s. The HDC will likely require replacement in-kind to create the original look, although there may be some leeway with respect to the material itself. After all, it’s all about keeping up appearances.

Second Empire, 1855 to 1880

The mansard roof is the character-defining feature of this style. A mansard is essentially a hipped gambrel. The lower roof, between the eaves and upper cornice, is most often covered in slate. More often than not, these parts of the roof can be restored and do not need to be replaced. If they do need replacement, be prepared to face an HDC that’s going to want it done in-kind. Keep in mind that these structures almost always have (or had) a built-in gutter at the eaves.
The sheet-metal linings fail, and replacement is expensive – especially if they failed long ago and wood rot has resulted from the neglect. The upper roof typically ranges from flat to a low-sloped 4:12 pitch. Once the roof becomes visible from the street, the material choice becomes important, and the same argument applied to Greek Revival and Italianate styles holds true here.

Queen Anne, 1880 to 1910

While the roof systems of many Queen Anne buildings, like this one in Portsmouth, NH, are complicated, more often than not the flashings need replacement, not the slate.Severe recessions in the U.S. during the 1870s stymied new construction. By the time the economy rebounded, the Queen Anne had replaced the Second Empire as the popular style of choice. Improvements in rail service, as well as material fabrication and production, were game changers. Architects and builders roofed these Victorians with various slate colors, cedar shingles, and flat-lock and standing-seam copper, along with different colors and shapes of clay tiles. And, often, these buildings have combinations of roofing materials and styles.

Unfortunately, many HDCs allow building owners to replace original roof fabric with so-called “architectural shingles.” These shingles were created to replicate wood shingle (or shake) roofs in an economical way. It is a fallacy that they are an appropriate alternative to slate; in fact, three-tab shingles look more like slate than architectural shingles do. Before you replace your entire roof, consider that it may only be the flashings that need replacement.

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