Guidelines For Locating New Ducts, Grilles, Light Fixtures And Switches In Historic Buildings

Technical Procedures Disclaimer

Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.


We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.

This standard includes general guidelines for locating new mechanical and/or electrical systems in historic buildings with minimal adverse impact on the building's appearance or character.


  • When possible, install new systems that are reversible.
  • Reuse existing holes where possible.
  • Use existing interstitial spaces to conceal systems.
  • Conceal wiring when possible.


  • Conceal piping and ductwork as much as possible, but DO NOT install suspended ceiling systems to do so.
  • If suspended ceiling systems must be installed, DO NOT allow system to abut glazing. The historic appearance of the window should be maintained where possible. This can be accomplished by "boxing" around window heads and leaving the complete window exposed to view.
  • Where piping cannot be easily concealed by providing alternative routes through less significant spaces, provide gypsum board enclosures of the minimum size necessary to sufficiently conceal the pipes.
  • Preserve ornamental walls and ceilings as much as possible. Avoid penetrating or attaching to ornamental finishes.
  • Where possible, place pipes, conduit, etc. along recessed ledges or other areas of minimal visibility.
  • Where possible use piping of minimum diameter for purposes specified.
  • Paint pipes, conduit, etc. where possible to blend with adjacent finishes.
  • Where possible, use decoration patterns to disguise new placement of wiring or systems.
  • Conceal ductwork in unused closets when possible and provide adequate ventilation.
  • Use an air-sampling system instead of a smoke detector when possible; only a small hole in the ceiling is required and very little space in the ceiling is required for the pipe.
  • Conceal sprinkler heads and smoke detectors in decorative ,plaster ceilings.
  • Use unused fireplaces for return air ducts.
  • Use permanently placed furniture to disguise ductwork.


  • Reuse original hardware, such as grilles, etc. where possible.
  • Specify new grilles, light fixtures, etc. to match original as closely as possible, in material and pattern.
  • If reuse of an existing grille is not possible, leave original grille in place and locate new grille within five feet of original location - preferably on a non-ornamental surface such as flat plaster.

Light Fixtures:

  • Rewire, clean and refinish original fixtures when possible.
  • NEVER attach fluorescent fixtures directly to ceiling medallions.
  • Conceal the light source when installing indirect lighting.
  • Introduce as few new fixtures and holes in the ceiling as possible.
  • Provide emergency lighting that is as unobtrusive as possible; use a small fixture if possible; make sure the battery pack is concealed.
  • Conceal ambient lighting behind ceiling moldings when possible.


  • Conceal Conduit For Light Switches, Fire Alarms And Other Controls Behind Decorative Surfaces If Possible Rather Than Attaching It Onto The Surfaces.
  • Paint Switch Plates And Access Panels Separately So They Can Be Easily Removed.
  • Conceal Fire Alarm Equipment Behind Unused Heating Grilles.
  • Use Wireless Fire Alarm Systems When Possible To Eliminate Unsightly Conduit And Wiring.
  • Conceal Electrical Panelboards In Unused Closets When Possible And Provide Adequate Ventilation
  • Conceal Smoke Detectors In Decorative Plaster Ceilings.