Historically-finished secondary interior spaces that have been previously modified and lack distinctive historic architectural features or finishes are usually less important in defining a building’s historic character and appearance. These spaces can often provide more opportunities for changes necessary for the continued or a new use of the building. However, when these historically-finished spaces remain in a finished condition at the start of a rehabilitation project, they still help define the building’s overall historic character and finished appearance. Any changes must not, therefore, alter the character of the spaces to the extent that they negatively impact the overall historic character of the property. (See related guidance on Changing Secondary Interior Spaces in Historic Buildings.)
When work begins on such spaces including demolition, environmental remediation, removal of interior finishes, or installation of new mechanical, electrical, and plumbing (MEP) systems, the spaces must generally be returned to a finished character and appearance at the completion of the project. Removing interior finishes and leaving structural systems or components exposed in a building that had finished spaces historically, such as in a Main Street-type commercial building, school, office, or apartment building, will change its character and, therefore not meet the Secretary of the Interior’s Standards for Rehabilitation (the Standards).
The examples below address some common problematic issues concerning historically finished spaces that were in a finished condition at the start of the project but that were left unfinished at the time of project completion and the submission of a Part 3 application requesting final certification. Whether the result of planned work not yet undertaken (e.g., a tenant space without a tenant secured), work not undertaken as approved in the Part 2 application, or work with unplanned effects (e.g., new plumbing drops or mechanical equipment serving the floors above that is not concealed within interstitial spaces and has been left exposed), such work can cause a project to not meet the Standards. Rather, it should be anticipated, planned for in advance, and coordinated during construction to avoid any potential issues at project completion. Otherwise, certification of a project may be jeopardized, or remedial work may be required for a project to be certified.
Unless otherwise noted, the following examples assume that the space being described is a historically-finished secondary space that had been previously modified and lacks distinctive historic architectural features, materials, or finishes, but remained a finished space at the start of the project. Ground-floor commercial tenant spaces are not typically considered to be secondary spaces for the purposes of the Standards and NPS guidance. However, they may often be treated similarly for the purposes of this guidance if they were historically finished, previously modified and lack distinctive architectural features and finishes, but remain in a finished condition at the start of the project. Further guidance and examples pertaining to both historically-finished secondary spaces and commercial tenant spaces can be found using the Preservation by Topic index.
Example 1. Exposed underlying masonry, half-timber, or frame construction in walls and ceilings in historically-finished secondary interior spaces.
Removing plaster or other finishes, including non-historic finishes, to expose portions of the underlying brick, stone, half-timber, or frame construction in historically-finished interior spaces will, in general, negatively impact the overall historic character of a property. These features and materials were never meant to be seen in buildings and spaces that were historically finished. Exposing portions of the underlying materials and structure of walls, ceilings, or other features, whether on a single floor or scattered throughout the building, or creating a distressed or deteriorated appearance, is unlikely to meet the Standards and may therefore require remedial work for a project to be certified.
Depending on the historic character of the building, the relative importance of the space(s), and the extent to which all the other completed work meets the Standards, there may be instances that such work, if discrete and limited, may not preclude the overall rehabilitation project from meeting the Standards. In such instances, the treatment should generally be limited and incidental in the context of the space(s) and the overall project, not affect the appearance of any nearby important historic features or materials, and generally not be highly visible from the exterior, primary interior spaces, or non-historic public and circulation areas of the building. Otherwise, plaster and other finishes should be retained in secondary spaces and ground-floor commercial tenant spaces.
Example 2. New mechanical, electrical, and plumbing (MEP) systems in historically-finished secondary interior spaces.
New MEP systems in historically-finished secondary interior spaces and ground-floor commercial tenant spaces, whether to serve a space itself or an adjacent one, should generally be concealed in order to preserve the historic character and appearance of the space and the building. Using existing soffits, chases, shafts, and interstitial spaces, where possible, is recommended. New soffits or chases to conceal MEP systems may be possible without negatively impacting the historic character of the space or creating obtrusive new features readily visible at windows from the exterior of the building. Examples include creating a new soffit in a secondary space behind a corridor wall to accommodate new HVAC ductwork or lowering a flat ceiling a few inches in order to accommodate new plumbing or ductwork, while still keeping the ceiling above the top of the window openings.
Conversely, a large soffit installed in a secondary space can, for example, sometimes more negatively impact the historic character and appearance of a space than an exposed sprinkler system or ductwork would if it is sensitively designed, sized, and located. Similarly, significantly lowering a ceiling to accommodate new plumbing or ductwork, depending on the depth required, can sometimes negatively change character-defining ceiling heights of the building or the proportions of the space. Also, lowering a ceiling below the tops of the windows can create soffits visible from the exterior of the building and impacts its exterior appearance.
In these cases, an exposed sprinkler system or limited mechanical ductwork may sometimes have less impact on historic character than concealing it, provided it is painted, simply configured, held close to the ceiling, and sensitively designed, sized, and located to be as visually unobtrusive as possible. [This may also be true for spaces that do retain historic ceiling features and finishes, such as an expressed structural system or a pressed metal or highly ornamented plaster ceiling, where concealing plumbing and ductwork in new soffits, ceiling clouds, and chases might be more visually intrusive and/or cause damage to the historic features.]
Exposed ceiling penetrations and plumbing drops in order to accommodate plumbing for the floors above can also negatively impact historic character. New ceiling penetrations should be concealed. Even in spaces that lack important architectural features and finishes, unless very few and very visually unobtrusive, they will rarely meet the Standards because of their impact on the character and appearance of the space and building.
Example 3. “White-box” condition of historically-finished secondary interior spaces and ground-floor commercial spaces for which a commercial tenant has yet to be identified.
The rehabilitation of historically-finished spaces used or converted to commercial tenant spaces in secondary interior spaces and ground-floor tenant spaces, even when the spaces lack distinctive architectural features or finishes but remained in a finished condition at the start of the project, must be carefully planned and considered. If features, finishes, and materials are removed from such spaces, the spaces must generally be returned to a finished condition at project completion to preserve the historic character and appearance of the building. Final commercial tenant buildouts in these spaces must have a finished appearance of walls, piers/columns, ceilings, floors, and mechanical/electrical/plumbing (MEP) systems and cannot leave unfinished materials exposed or walls and ceilings in a deteriorated or “distressed”-appearing condition.
Often, commercial tenants may not yet have been identified, and, consequently, tenant buildouts may not be completed at the time of project completion and the submission of the Part 3 application. Given the commercial nature of rental spaces, it is common practice for them to be left largely unfinished and not built out until which time the space has been leased. As part of preparing these spaces for future tenants, and while work crews are already mobilized, remaining buildouts from prior tenants are also often removed (i.e., “commercial strip-outs”), and wall, ceiling, and floor finishes and materials may also be removed for mold, asbestos, and lead paint remediation reasons.
A so-called “white-box” condition — with a finished ceiling and walls, including piers and columns, plastered or drywalled and prepped for painting; and concealed mechanical, electrical, and plumbing (MEP) systems — is often undertaken to return a space to a finished condition and appearance before a tenant has been identified, and it will generally be necessary for the purposes of Part 3 certification for secondary spaces and ground-floor commercial tenant spaces that were historically finished and lack distinctive historic architectural features, materials, or finishes, but remained a finished space at the start of the project.
Sometimes the cost, time, and uncertainty of undertaking what otherwise may be speculative or unnecessary work to “white-box” a space for a future, yet-to-be-identified tenant can be considerable, particularly as part of larger rehabilitation projects. Under certain conditions and circumstances as further described in the examples below, an alternative to a “full” white-box treatment (i.e., finished walls/ceilings and concealed MEP systems) may also be accepted for the purposes of Part 3 certification:
- Minimum-Accepted White-Box Condition
- Selective Demolition/Commercial Strip-Out
- When a Commercial Tenant Space May be Left Unfinished
- When Multiple Commercial Tenant Spaces May Be Left Partially Unfinished
Minimum-Accepted White-Box Condition
For small-scale, low-rise buildings, in particular, such as “Main Street-type” buildings, where the commercial tenant spaces constitute a significant portion of the building, and therefore have a correspondingly greater impact on its overall historic character and appearance, a “full” white-box treatment (i.e., finished walls/ceilings and concealed MEP systems, as defined above) will generally be required.For larger buildings, however, a “partial” white-box treatment of tenant spaces — defined as just finished walls, including piers and columns, plastered or drywalled and prepped for painting, but not including finished ceilings or concealed MEP systems — will generally be sufficient in most instances for the treatment of these spaces to be considered complete for the purposes of Part 3 certification. In such cases, ceilings and floors may be left in an unfinished or partially unfinished condition until which time a tenant is identified. Any MEP systems directly associated with wall surfaces should generally still be concealed, but need not be completely finished (e.g., mounted electrical boxes should be flush with drywall surfaces, but need not have had wall plates installed). Primary interior spaces, including non-historic public and circulation areas, must still be returned to a full finished condition (i.e., finished wall surfaces, ceilings, floors, and MEP systems).
However, even in such instances, if the large majority of the interior spaces of the building will consist of nothing but partially white-boxed spaces, such as for a multi-story speculative commercial office building where none to few tenant spaces may have been leased and built out by the time of project completion, additional white-boxing of ceilings and/or MEP systems may be required so that the building retains a sufficient overall finished condition and appearance at the time of Part 3 certification.
Questions about whether a specific building might be considered one large enough for the purposes of this alternative white-box treatment to apply or about what the minimum-accepted treatment might be in such instances may be directed to the State Historic Preservation Office (SHPO), who will consult with the NPS as necessary.
Selective Demolition/Commercial Strip-Out
Removing later, non-historic commercial tenant buildouts (i.e., non-historic fixtures, finishes, and furniture) will generally not require further white-box treatments as long as, underneath the non-historic materials, a plaster, drywall, or other such finish remains on wall surfaces, piers, and columns, and the space still largely conveys an overall finished appearance. However, if remaining exposed finishes have been so removed or further damaged in the selective demolition process, giving the walls a deteriorated or “distressed” appearance, or no such finishes remain once later non-historic tenant buildouts have been removed, then the partial white-box condition described above of wall surfaces, including piers and columns, may still be required for Part 3 certification, depending on the specific conditions and appearance.Interior spaces that were originally constructed with an acoustical panel ceiling may have never had finishes above the suspended ceiling. While not necessary for white-boxing purposes at Part 3 certification, these spaces must still have a new, compatible finished ceiling treatment as part of any future tenant buildout if the acoustical panel ceiling is proposed to be removed (and is not itself considered character-defining – see guidance on Historic Acoustical Panel Ceilings and Residential and Hotel Conversions).
When a Commercial Tenant Space May be Left Unfinished
In some limited instances, leaving a commercial tenant space unfinished, such as one ground-floor space in a large, multi-story building, may not negatively impact its overall historic character and, therefore, the ability for Part 3 certification to be issued.Conversely, an unfinished tenant space in a smaller building, such as a ground-floor or second-floor tenant space of a small two-story “Main Street-type” commercial building, would generally have a greater impact on the overall historic character of the building and may preclude certification. Ground-floor commercial tenant spaces are often more important than upper-story tenant spaces to the historic character of a building because they are generally more public and visible, as well as can be more important to the historic character and appearance of specific buildings and building types.
In the context of an overall project that otherwise meets the Standards for Rehabilitation, the extent of any tenant spaces left unfinished must be minor, not highly visible, and relatively incidental in the context of the specific floor(s) of the building and/or the historic character of the overall building generally.
When Multiple Commercial Tenant Spaces May Be Left Partially Unfinished
Leaving multiple commercial tenant spaces partially unfinished may also not negatively impact the overall historic character of the building in some instances, depending on the number, proportional area, relative visibility, and historic character of the spaces, as well as the extent of any white-box treatments undertaken in the spaces to walls and other surfaces. The acceptability of such proposed treatments for the purposes of Part 3 certification will be considered on a case-by-case basis to the extent it might be considered equivalent to the minimum white-box requirements described above. Such proposed treatments should be discussed in advance with the SHPO, who will consult with the NPS as necessary.Applying this Guidance on White-Box Conditions and Treatments
The Part 2 application should address how commercial tenant spaces in secondary interior spaces and ground-floor tenant spaces will be treated as part of the overall scope of work for the rehabilitation project. This can include a description of the actual proposed tenant buildout(s), if known; the identification of the tenant buildout(s) as a future phase, for which the proposed work will be submitted for review and approval when available; and/or a description of the proposed treatment pursuant to this guidance on white-box conditions and treatments.
For tenant spaces for which this guidance is proposed to be used, the treatment should be submitted for NPS review and approval prior to undertaking such work, either as part of the original Part 2 application or as a later Amendment. The description should address how the proposed treatment conforms with this guidance, as well as, in the case of later Amendments, whether there are any changes to the proposed treatment of other tenant spaces previously reviewed and approved.
In all instances, the description of such proposed work should specify that the tenant spaces will be returned to a finished condition and appearance as part of any future tenant buildout(s) and that the buildout(s) will be submitted for prior review and approval by NPS/SHPO when available.
In addition, for this guidance to apply:
- Other work that may have been undertaken in the subject space(s) such as completed mechanical ductwork and ceiling penetrations for plumbing drops must be consistent with the approved description of work or otherwise meet the Standards for Rehabilitation.
- If ceilings are proposed to be finished or modified, such as to meet code or other requirements for fire separation, sound attenuation, etc., then affected ceiling surfaces should not be left in a partially unfinished condition and should minimally receive a white-box treatment (i.e., plastered or drywalled, and prepped for painting) as part of this work. Similarly, if other than temporary or partial ductwork systems are installed, then the systems should be concealed.
- Spaces that retain some historic features, materials, or finishes, such as a decorative pressed-metal ceiling or sections of crown moldings and trim, may not be subject to this guidance. Depending on the specific facts and circumstances, these spaces may need to be returned to a full or partial white-box condition or otherwise finished condition, depending on their importance to the historic character and appearance of the property and the space.
For any spaces for which a use or tenant has yet to be identified at the time of project completion, the work for proposed tenant buildout(s), when available, should be submitted for NPS review and approval if the work is to be undertaken post-Part 3 certification within five years of completion of the project. The spaces must be fully returned to a fully finished condition and appearance (i.e., finished wall surfaces, ceilings, floors, and MEP systems) at that time.
If any commercial tenant spaces are leased and actively used without having been fully returned to a finished condition and appearance of walls, piers/columns, ceilings, floors, and mechanical/electrical/plumbing (MEP) systems), the overall project will not be considered to have been undertaken as represented in the application or otherwise in conformance with NPS certification of the project and the Standards for Rehabilitation, in which case the Part 3 certification of the project may be subject to revocation pursuant to 36 CFR 67.6(e-f).
Please note that states may have separate requirements regarding white-box treatments for the purposes of state historic tax credits which may or may not be the same as NPS requirements for the purposes of Part 3 certification described in this guidance. Also, the completed rehabilitation project must still meet the Internal Revenue Code requirements to claim the Rehabilitation Tax Credit, and tenant buildouts undertaken post-Part 3 certification may not qualify for the purposes of claiming federal or state credits, depending on the timing of when the work is undertaken and other factors. Lastly, state and local building and zoning codes may also require white-box treatments beyond the minimum accepted for the purposes of Part 3 certification.
Revised March 2026
Last updated: March 30, 2026