Substitute materials: Weighing pros and cons in exterior restoration

Sustainability considerations

The significant terra cotta cornice cracking and deterioration shown here requires replacement units.

Material selection not only influences the performance and longevity of buildings, but also affects the health of the environment. At a minimum, material choices concern the local ecology in and around a building, which is commonly affected by the issue of hazardous materials. If a component to be replaced contains hazardous material such as asbestos, polychlorinated biphenyls (PCBs), or lead, it not only concerns abatement procedures, but it also could be more reason to comprehensively replace all the existing material with a substitute material, especially if the hazardous compound is friable and will be disturbed by the project, or if it presents ongoing health issues.

Beyond the realm of the immediate building ecology, other questions emerge about the potential long-term damage or benefits in using certain materials. This should include an analysis of material lifecycle and disposal. Many traditional natural materials like stone and clay masonry and old growth wood, if carefully removed, can be repurposed. Stone and clay materials can be crushed to be used as aggregate in concrete or for roof ballast or landscaping. Wood is inherently biodegradable and can help feed other organisms as it decays. While several substitute materials might contain natural material components, like precast concrete, cement fiber board, or wood byproducts, many contemporary substitutes are synthetic. Some substitutes contain plastic, which is not biodegradable but may be recyclable, while others contain bitumen or fiberglass, which can be toxic, cause irritation, or contribute to pollution. Many traditional natural materials also benefit from having a lower carbon footprint and embodied energy. Since they are less processed, less energy is consumed in their extraction and fabrication. Moreover, the energy consumed in material production is often not “green,” as it typically pumps carbon into the atmosphere, which contributes to climate change.

Although natural materials can have environmental benefits, using them may not always be the best option for a given project. Technologies are ever evolving, and production processes continue to be refined as environmental regulations gain further ground. Therefore, it falls upon the design professional to research products and include sustainability criteria when developing specifications. Choosing materials that are locally sourced is a good start, as less energy is consumed in delivery. Where possible, careful reconsideration of material color can affect a building’s energy use. Lighter color materials typically have higher albedo, meaning they reflect more sunlight and reduce solar heat gain. Increasingly, building codes are including albedo requirements by establishing a minimum Solar Reflectance Index (SRI), especially for roofing, since it typically has the most direct sun exposure. Additionally, when large portions of building enclosures are replaced, considering the insulation value of materials used, and how their connections impact thermal bridging, is also critical to evaluating energy performance.

It is also important to consider how material selection affects the type and frequency of required maintenance for the enclosure. Although the introduction of substitutes may appear to solve some availability, cost, or schedule issues, they may not be providing savings in the long-term. If materials must be replaced more often or cause adjacent materials to have to be replaced sooner than anticipated, they are only further contributing to landfills and excessive resource consumption.

Philosophical and historical conclusions

When exposed to heat, thin marble is susceptible to hysteresis, resulting in panel displacement and open panel joints.

The use of substitute materials is not a new concept. Their history shows how their implementation is part and parcel to the evolution of architecture. Although now considered historically valuable, terra cotta was commonly employed as a substitute for more expensive stone at the turn of the century. For centuries, wood has been painted with sand to look like stone and was common in American and European manor houses. Romans used concrete and brick in lieu of monolithic stone, primarily for backup materials, to achieve efficiency, as poured materials or smaller units could be installed more quickly.

During the Industrial Revolution, iron and steel replaced wood structures, and when first employed, metal structures used wood joinery techniques, like mortise and tenon, as new metal joints had not yet been invented. Even ancient Greek buildings had decorative elements which reflected the evolving history of material use. Many temples were originally constructed in wood, and the triglyphs, a projecting part of the decorative entablature above the perimeter columns, represented the rough-cut ends of wood beams used in these earlier constructions. These latter examples reinforce the notion of palimpsest within architecture, something altered over time that still bears marks of its original form.

Buildings are ever-changing, living entities that require regular repair and maintenance, regardless of the materials and assemblies used. Some degree of replacement material is unavoidable, as even repairs typically involve piecemeal removal and replacement of portions of original units, such as patching compounds and joint materials. So, the notion of replacement might be as much a matter of perspective as matching “in-kind” can be.

These arguments may only seem relevant to historic and landmark buildings, but many contemporary structures could one day be considered historically valuable, which is increasingly the case for modernist style buildings. Even structures built in the 1970s are receiving increased attention, since they are now 50 years old. The issue of substitute materials has unique challenges for buildings of this era. The industrial products they often used, considered revolutionary for their time, might now be obsolete, and they can contain hazardous materials.

Perhaps buildings should be allowed to be patchworks which reflect the passing of time and the signature of all those who worked on them. Like cathedrals that took several decades to build and incorporate multiple styles and materials, or historic cities which took centuries to accumulate, construction is an amalgam of influences. Does an edifice lose its authenticity or cultural value from too much alteration, repair, or restoration? Is Sagrada Familia less authentic because it is being constructed with modern technologies different from those available during Guadi’s lifetime? Are the building’s tectonics, its art of construction, corrupted by use of substitutes since these might compromise the original designer’s intentions?

On the other hand, design professionals should combat the common misconception that newer is necessarily better. Although substitute materials are now subject to regulated engineering and testing, in the greater history of material use, many of them are still relatively new. It is not entirely known how some of them will perform in the long-term, either independently or as part of an existing assembly. The answer to which material to use is not necessarily straightforward and should be evaluated on a case-by-case basis.


Richard W. Off is a senior project manager and registered architect at Hoffmann Architects in Manhattan, New York. With a focus in historic preservation, and expertise in traditional and modern facade, roofing, and window systems, he oversees A+E teams complete numerous multimillion-dollar investigation, rehabilitation, renovation, and adaptive reuse projects throughout the New York metropolitan area. He graduated with a Master of Architecture and Urban Design from Columbia University and a Bachelor of Architecture from Rensselaer Polytechnic Institute. Off has lectured at traditional building conferences, the APT DC Symposium, and both his alma maters. An avid writer, he has also published articles with The Construction Specifier.

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