To meet Standard 1, which states that a property shall be placed in a new use that requires minimal change to the defining characteristics of the building, it must be determined whether an historic building can accommodate a new addition. Before expanding the building’s footprint, consideration should first be given to incorporating changes—such as code upgrades or spatial needs for a new use—within secondary areas of the historic building. After such an evaluation, the conclusion may be that an addition is necessary, particularly if it is needed to avoid modifications to character-defining interior elements. The addition must be designed to be compatible with the historic character of the building and thus meet the Secretary of the Interior’s Standards for Rehabilitation.
In accordance with Standard 9, a new addition must preserve the historic building’s form/envelope, significant materials and features; must be compatible with the historic building’s massing, size, scale, and architectural features; and must be differentiated from the historic building to preserve its character. Standard 10 calls for new additions to be constructed in such a manner that the essential form and integrity of the historic property be unimpaired if the new work were to be removed in the future. Limiting the removal of historic materials and utilizing existing doors or enlarging windows to transition to the new addition may accomplish this. The Guidelines for Rehabilitating Historic Buildings also recommend locating a new addition at the rear or on an inconspicuous side of a historic building. Additional NPS guidance is contained in Interpreting the Standards Bulletins and Preservation Brief 14: New Exterior Additions to Historic Buildings: Preservation Concerns.
There is no formula or prescription for designing a compatible new addition. A new addition to a historic building that meets the Standards can be any architectural style—traditionalist, contemporary or a simplified version of the historic building. However, there must be a balance between differentiation and compatibility in order to maintain the historic character and the very identity of the building being enlarged. New additions that are either identical to the historic building or in extreme contrast to it fall short of this balance. Inherent in all of the guidance is the concept that an addition needs to be subordinate to the historic building. General parameters are outlined below to provide guidance and to assist building owners in meeting the Standards.
Placement or location of the new addition on the site
A new addition is most appropriately located where its visibility from the primary views of the historic building is minimized. This is often a rear or obscure elevation. However, rear or side elevations may not always be sufficiently secondary to be suitable locations for an addition, particularly when a historic building is visually prominent from many vantage points.
Site characteristics therefore, are significant factors to consider in the process of determining the appropriate location for a new addition. When planning an addition, preserving significant landscape features – including vegetation, grading, walls, fences, walkways, driveways – and other important historic features of the historic property must be taken into account. Furthermore, significant archeological resources must also be considered when evaluating the placement of an addition and, as appropriate, mitigation measures must be implemented if they are to be disturbed.
A careful site analysis can identify suitable locations for an addition that take advantage of site features such as topographic changes and other factors that may lessen the impact of an addition. Opportunities for locating an addition partially or entirely below ground, or set behind other site features that can screen the visibility of new construction should be evaluated.
Size, scale, and massing of the new addition
The size, scale, and massing of a new addition all pertain to the addition’s overall volume and three-dimensional qualities. Taken together, size, scale and massing are critical elements for ensuring that a new addition is subordinate to the historic building, thus preserving the historic character of a historic property. Typically, a compatible addition should be smaller than the historic building in both height and footprint. However, there are other considerations that may allow moving away from this basic concept.
Depending on its location, it may be possible that an addition slightly taller or slightly larger than the historic building may be acceptable, as long as it is visually subordinate to the historic building. In some cases, separating the addition from the historic building with a small hyphen can reduce the impact of an addition that is larger than the historic building. Another way of minimizing the impact of a new addition to an historic building is to offset it or step it back from the mass of the historic building.
Differentiating the new addition from the historic building
To preserve a property’s historic character, a new addition must be visually distinguishable from the historic building. Section 67.7(c) of the program regulations cautions “exterior additions that duplicate the form, material, and detailing of the structure to the extent that they compromise the historic character of the structure will result in denial of certification.” This does not mean that the addition and historic building should be glaringly different in terms of design, materials and other visual qualities. Instead, the new addition should take its design cues from, but not copy, the historic building.
Differentiating the new from the old, yet still respecting the architectural qualities and vocabulary of the old, can be accomplished through a variety of design techniques, including:
- Incorporating a simple, recessed, small-scale hyphen to physically separate the old and the new volumes or setting the addition back from the wall plane(s) of the historic building.
- Avoiding any approaches that unify the two volumes into a single architectural whole. The coordination of individual features between the new addition and the historic building will not necessarily impair the existing building’s historic character as long as the new structure is clearly differentiated and distinguishable as a new addition so that the identity of the historic structure is not lost altogether in a new and larger composition. The historic building must be clearly identifiable and its physical integrity must not be compromised by the new addition.
- Using building materials in the same color range or value as those of the historic building. The materials used on the new addition need not be the same as those on the historic building; however, new materials that highly contrast the historic ones should be avoided.
- Basing the size, rhythm and alignment of the new addition’s window and door openings on those of the historic building.
- A new addition should also respect the architectural expression of the historic building type. For example, an addition to an institutional building should maintain the architectural character associated with this building type rather than using details and elements typical of residential or other building types.
The techniques listed above are merely examples of ways to differentiate a new addition from the historic building while ensuring that the addition is compatible with it. Other ways of differentiating a new addition from the historic building may be used as long they maintain the primacy of the historic building.
Working within these basic principles still allows for a broad range of architectural expression that can range from stylistic similarity to contemporary distinction. The recommended design approach for an addition is one that neither copies the historic building exactly nor stands in stark contrast to it.
New additions in densely-built environments
A densely-built neighborhood such as a downtown commercial core offers an opportunity to design an addition that can have a minimal impact on the historic building. Often the site for such an addition is vacant land where an independent building formerly stood. Treating the addition as a separate or infill building may be the route to having the least impact on the historic building. In these instances there may be no need for a direct visual link to the historic building, but the addition must still respect the scale of the historic building and those around it. Height and setback from the street should generally be consistent with those of the historic building and other surrounding buildings. There may be an opportunity for a larger addition when the facade of the addition can be broken up into elements that are consistent with the scale of the historic building and the adjacent building.
New additions in historic districts
When a building’s historic status derives from its inclusion in an historic district, it is also necessary to look beyond the building itself in evaluating an addition. Relevant guidance comes from 36 CFR Part 67.6 (b)(6), of the program regulations and this guidance makes clear that all aspects of a rehabilitation, including a new addition, will be reviewed first as they affect the historic building and second as they affect the district in which the building is located. Additions to historic buildings may not cause the demolition of an adjacent certified historic structure for a rehabilitation project seeking certification according to 36 CFR Part 67.6 (b)(5).
Last updated: September 15, 2022