PART 4 PRESERVATION MONTH 2020 SERIES
LAST WEEK WE PRESENTED PART 3 on the Economic Benefits of Preservation. Part 4 of this series focuses on substitute materials. “Substitute” may not be the first word that comes to mind when we think of preservation, and anyone who knows us knows that we try to preserve, maintain, and repair existing structures and features whenever possible. However, the use of substitute materials in building is not new (even George Washington used wood painted with sand to simulate stone). And, although one of the primary goals of preservation is the retention of original materials – preserve, maintain, repair, and replace is the “order of operations” according to the Secretary of the Interior – sometimes replacement is necessary when the preceding steps are no longer an option. Read on to find out more about deciding when and what substitute materials to use.
Photo by Annie Spratt on Unsplash
REPAIR OR REPLACE:
It is easy to think that if the look of a historical building is maintained and the appropriate types of materials are used, that the building has been successfully preserved. But preservation is not just about preserving how something looks, it is primarily focused on preserving how something is so that it remains as original as possible for future generations.
The National Park Service considers repair preferable to replacement, to save as much of the original material and historic fabric as possible.
- REPAIR. The following are some of their reasons for repair vs. replacement:
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- Cost. It may be more costly in some cases to use substitute materials, depending on the situation, so using the original material (even if it is harder to find) may be more cost-effective in the long-term.
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- Durability. Substitute materials are typically less durable than original materials, rendering originals far superior. Do not fall for the “maintenance free” trap.
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- Skill and knowledge. If you or the person doing the work on your building are not knowledgeable about original or substitute materials and their appropriate installation, you might run into several issues that make problems worse. A typical example of this is old brick and new mortar.
If repair is not sufficient, the National Park Service reports that the purpose of replacing is to “match visually what was there and to cause no further deterioration.”
- REPLACE – The following are 4 circumstances described by NPS as warranting replacement:
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- Availability of material. It can be difficult to find a good match for historic material, particularly masonry materials due to uniqueness of color and texture. Also, some material is unavailable or may take too long to arrive, in which case a good substitute should be considered.
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- Availability of craftspeople. There may not be as many skilled craftspeople as there were in the past. However, there are people available, and it is important to make every effort to find someone to make the replacement as accurate as possible.
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- Poor original material. Just because something is historic does not always mean it is of good quality. Some materials were poor, naturally incompatible with their building, or have inferior modern substitutes. Examples of such materials include historic soft sandstones that are prone to erosion, or poor quality modern tin coated steel roofing. These might be replaced by precast concrete and terne-coated stainless steel, respectively.
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- Code-related changes. One example is buildings in earthquake zones, which are now subject to laws requiring that heavy overhanging masonry and unsecured urns be re-anchored or removed. Appropriate replacements include lighter replicas (although this may interfere with National Register status and loss of Federal tax credits for rehabilitation).
REPLACEMENT TYPES
- Replacement in-kind. This is a gold-standard level of replacement, and the Secretary of the Interior’s Standards for treatment of historic properties indicate this is the first choice when things are damaged beyond repair (e.g., replace “marble for marble, wood for wood”). We’ve discussed this in the past as well.
- Replace with substitute materials. The National Park Service outlines the Secretary of the Interior’s points on how to address this. They suggest that if replacement in-kind is not possible, substitute materials may be considered. Circumstances warranting substitute materials include:
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- Original materials have performed poorly
- No source for original materials
- Craftspersons are not available to replicate the historic element in its original material
- Current code requirements do not permit the use of the historic material.
STEPS TO REPLACEMENT:
- Is replacement necessary? The Secretary of the Interior’s standards encourage assessing if replacement is necessary (see steps outlined above in this article, as well as the replacement types).
- Assess amount/location of replacement material. The standards state that the amount and location of replacement material must be evaluated in relation to the building’s historic character – which NPS defines as a combination of its history, materials used, and degree of craftsmanship. The degree of contribution to character by the building feature in question may require a closer replacement match, compared to another building part that contributes less or is not as visible or distinctive. Excessive reliance on substitute materials is cautioned against.
- Consider appropriateness of substitute material. The standards state that the appropriateness of a particular substitute material must also be considered in regard to its appearance and other factors, such as the location of the application, and the known physical compatibility of the substitute material relative to the historic material. Substitute materials must closely match the original feature. They must also be physically and visually compatible in context of nearby features and the entire building (e.g., new mortar does not work with historic brick due to physical incompatibilities).
Although this is our final post in the PRESERVATION MONTH 2020 SERIES, we hope that you will continue to put preservation first every month hereafter. To get you started, you can find further, more in-depth information on substitute materials from the following resources:
- National Park Service’s Technical Preservation Services standards for substitute materials
- National Park Service’s Technical Preservation Services standards on building exteriors
- National Alliance of Preservation Commission’s Spring 2019 Quarterly Journal on Alternative Materials for Historic Buildings
- Our piece on choosing replacement materials