If new ceilings must be installed, insure that they do not
come close to systems that would be designed for a new
block any light from the top of existing windows or alter
building, within the obvious limits of available physical
the appearance of the building from the outdoors. Original
space and structural capacity.
plaster ceilings in significant spaces such as lobbies and
In the third instance, where a historic structure is to
corridors shall be retained, to the extent possible, and
be altered, special documents shall be provided by GSA
modified only as necessary to accommodate horizontal
to help guide the design of the alterations. The most
distribution. Use soffits and false beams where necessary
important of these is the HBPP that identifies zones of
to minimize alteration of overall ceiling heights.
architectural importance, specific character-defining
In buildings containing ornamental or inaccessible
elements that shall be preserved, and standards to be
ceilings, piping and ductwork shall have to be routed in
employed. See Chapter 1: General Requirements, General
furred wall space or exposed in the occupiable building
Design Philosophy, Historic Buildings.
area. Exposed ducts must be designed to complement the
When a system is designed, it is important to anticipate
building architecture in forms and materials used. Use
how it will be installed, how damage to historic materials
of exposed ducts is encouraged in locations where
can be minimized, and how visible the new mechanical
concealing ducts would obscure significant architectural
system will be within the restored or rehabilitated space.
surfaces or details, such as vaulted ceilings. Exposed
ducts shall also be considered in historic industrial
The following guidelines shall be followed for HVAC work
buildings and open plan, tall ceiling, high window spaces
in historic buildings:
suited to flexible grid/flexible density treatments.
Design HVAC systems to avoid impacting other systems
If new vertical air distribution risers are required, they
and historic finishes, elements and spaces.
shall preferably be located adjacent to existing shafts.
Place exterior equipment where it is not visible. Recess
Reduce heating and cooling loads to minimize size and
equipment from the edge of the roof to minimize visibility
other impacts of modern equipment.
of the equipment from grade. Alternatively, explore
Calculate the effect of historic building features such as
creating a vault for easier access to large mechanical
wall thickness, skylights, and porticos, interior design
equipment. If equipment cannot be concealed, specify
features such as draperies, shutters and window shades,
equipment housings in a color that will blend with the
and existing site features such as landscaping.
historic face. As a last resort, enclose equipment in
Select system types, components, and placement to
screening designed to blend visually with the facade.
minimize alteration of significant spaces. In previously
Locate equipment with particular care for weight and
altered spaces, design systems to allow historic surfaces,
vibration on older building materials. These materials
ceiling heights, and configurations to be restored. Reuse
cannot accept the same stress as when the equipment is
of HVAC system elements is only permitted with written
used in newer construction.
documentation obtained from GSA Property Management
by the A/E.
167
MECHANICAL
ENGINEERING
5.19
Alterations in Existing Buildings and Historic Structures
Revised March 2005 PBS-P100
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