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.
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.
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
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
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
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.
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.
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.
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.
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.
Installing a new mechanical system so that character-defining
structural or interior features are radically
changed, damaged, or destroyed.
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
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
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