<photo>Detail of window arches above a rehabilitated storefront;  Link to National Park Service
<photo>operational historic boiler

Identify    Protect    Repair    Replace   Alterations/Additions

Identify, Retain and Preserve

Identifying, retaining, and preserving visible features of early mechanical systems that are important in defining the overall historic character of the building, such as radiators, vents, fans, grilles, plumbing fixtures, switchplates, and lights.

photos of early 20th century interior lighting (left) and elevators (right)

The greatest impact of the 20th century on mechanical systems included the use of electricity for interior lighting (left) and elevators for tall buildings (right). The new age of technology brought an increasingly high level of design and
decorative art to the functional elements of mechanical, electrical and plumbing systems. Photos: NPS files.

Not Recommended
Removing or radically changing features of mechanical systems that are important in defining the overall historic character of the building so that, as a result, the character is diminished.

Protect and Maintain

Protecting and maintaining mechanical, plumbing, and electrical systems and their features through cyclical cleaning and other appropriate measures.

Preventing accelerated deterioration of mechanical systems by providing adequate ventilation of attics, crawlspaces, and cellars so that moisture problems are avoided.

photo showing how awnings may be used to reduce the need for elaborate new mechanical equipment

In the past, awnings were used extensively to provide shade to keep buildings cooler in the summer. If awnings are in place, keep them in good condition, and take advantage of their energy-saving contribution. If awnings are added, they need to be installed without damaging the building or visually impairing its architectural character. Photo: NPS files.

Improving the energy efficiency of existing mechanical systems to help reduce the need for elaborate new equipment. Consideration should be given to installing storm windows, insulating attic crawl space, or adding awnings, if appropriate.

Not Recommended
Failing to provide adequate protection of materials on a cyclical basis so that deterioration of mechanical systems and their visible features results.

Enclosing mechanical systems in areas that are not adequately ventilated so that deterioration of the systems results.

Installing unnecessary air conditioning or climate control systems which can add excessive moisture to the building. This additional moisture can either condense inside, damaging interior surfaces, or pass through interior walls to the exterior, potentially damaging adjacent materials as it migrates.


Repairing mechanical systems by augmenting or upgrading system parts, such as installing new pipes and ducts; rewiring; or adding new compressors or boilers.

Not Recommended
Replacing a mechanical system or its functional parts when it could be upgraded and retained.


Replacing in kind--or with compatible substitute material--those visible features of mechanical systems that are either extensively deteriorated or are prototypes such as ceiling fans, switchplates, radiators, grilles, or plumbing fixtures.

Not Recommended
Installing a visible replacement feature that does not convey the same visual appearance.

The following work is highlighted to indicate that it represents the particularly complex technical or design aspects of Rehabilitation projects and should only be considered after the preservation concerns listed above have been addressed.

Alterations/Additions for the New Use

Installing a completely new mechanical system if required for the new use so that it causes the least alteration possible to the building's floor plan, the exterior elevations, and the least damage to the historic building material.

Providing adequate structural support for new mechanical equipment.Installing the vertical runs of ducts, pipes, and cables in closets, service rooms, and wall cavities.

photo of a basic HVAC system installed in a non-significant interior space

The basic heating, ventilation and air conditioning (HVAC) system, composed of compressor drives, chillers, condensers, and furnace, has been installed here in a non-significant space so that it does not impact the historic character of the interior. Photo: NPS

Installing air conditioning units if required by the new use in such a manner that historic features are not damaged or obscured and excessive moisture is not generated that will accelerate deterioration of historic materials

.Installing heating/air conditioning units in the window frames in such a manner that the sash and frames are protected. Window installations should be considered only when all other viable heating/cooling systems would result in significant damage to historic materials.

Not Recommended
Installing a new mechanical system so that character-defining structural or interior features are radically changed, damaged, or destroyed.

photo showing how through-the-wall air conditioners destroy historic building material

Historic building material is destroyed by installation of
through-the-wall air conditioners. Photo: NPS files.

Failing to consider the weight and design of new mechanical equipment so that, as a result, historic structural members or finished surfaces are weakened or cracked.

Installing vertical runs of ducts, pipes, and cables in places where they will obscure character-defining features.

Concealing mechanical equipment in walls or ceilings in a manner that requires the removal of historic building material.Installing a "dropped" acoustical ceiling to hide mechanical equipment when this destroys the proportions of character-defining interior spaces.

Cutting through features such as masonry walls in order to install air conditioning units.

Radically changing the appearance of the historic building or damaging or destroying windows by installing heating/air conditioning units in historic window frames.




The Approach

Exterior Materials
Architectural Metals

Exterior Features
Entrances + Porches

Interior Features
Structural System Spaces/Features/Finishes
Mechanical Systems



Special Requirements
Energy Efficiency
New Additions
Health + Safety

The Standards



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