Energy efficiency in historic buildings

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Although the work in this section is quite often an important aspect of rehabilitation projects, it is usually not part of the overall process preservations experts from the National Park Service recommend in restoring historic structures: identify, protect, repair, replace, recreate.

Work on energy efficiency is assessed for its potential negative impact on the building's historic character. For this reason, particular care must be taken not to obscure, radically change, damage, or destroy character-defining features in the process of rehabilitation work to make the building more energy efficient.

This section is divided into work associated with energy efficiency in these areas: 1) wood, masonry, architectural metals; 2) windows; 3) entrances and porches; 4) interior features; 5) mechanical systems; 6) building site; 7) setting (district or neighborhood); and 8) new additions to historic buildings.

As with the other installments in this series, the U.S. Secretary of the Interior's recommendations for historic rehabilitation are followed by a "Not Recommended" section. Items in the "Not Recommended" sections are likely to damage or destroy the historic character of a building.

Energy Efficiency: an introduction

01.jpg (22894 bytes)Some features of an historic building or site such as cupolas, shutters, transoms, skylights, sun rooms, porches, and plantings also play a secondary energy-conserving role. At right, a traditional canvas awning reduces heat gain.

Therefore, prior to retrofitting historic buildings to make them more energy efficient, this first step should always be taken: identify and evaluate existing historic features to assess their inherent energy-conserving potential.

If it is determined that retrofitting measures are necessary, then such work needs to be carried out with particular care to ensure that the building's historic character is retained.

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1) Masonry, wood, architectural metals

03.jpg (16476 bytes)Install thermal insulation in attics and in unheated cellars and crawl spaces to increase the efficiency of the existing mechanical systems.

Install insulating material on the inside of masonry walls to increase energy efficiency where there is no character-defining interior molding around the window or other interior architectural detailing.

In this photo, workers are insulating the attic and installing a replacement composition roof on this 1920s house.

Not recommended:

  • Applying thermal insulation with a high moisture content into wall cavities. This may damage historic fabric.
  • Installing wall insulation without considering its effect on interior molding or other architectural detailing.

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2) Windows

07.jpg (29933 bytes)Use the inherent energy conserving features of a building by maintaining windows and louvered blinds in good operable condition for natural ventilation.

Improve thermal efficiency with weather-stripping, storm windows, caulking, interior shades, and if historically appropriate, blinds and awnings.

In the photo at right, well-maintained louvered shutters allow for ventilation and privacy.

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Install interior storm windows with air-tight gaskets, ventilating holes, and/or removable clips to insure proper maintenance and to avoid condensation damage to historic windows.

Install exterior storm windows which do not damage or obscure the windows and frames.

In this photo, storm doors have been added on the inside of historic doors.

Not recommended:

  • Removing historic shading devices rather than keeping them in an operable condition.
  • Replacing historic multi-paned sash with new thermal sash with false muntins.
  • Installing interior storm windows that allow moisture to accumulate and damage the window.
  • Installing new exterior storm windows which are inappropriate in size or color.
  • Replacing windows or transoms with fixed thermal glazing or permitting windows and transoms to remain inoperable rather than using their energy conserving potential.

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3) Entrances and Porches

04.jpg (16170 bytes)Maintain porches and double vestibule entrances so that they can retain heat or block the sun and provide natural ventilation.

The porch at left reduces heat gain from the sun.

Not recommended:

  • Changing the historic appearance of the building by enclosing porches.

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4) Interior features

09.jpg (21271 bytes)Retain historic interior shutters and transoms for their inherent energy-conserving features.At right, the operable over-the-door transom provides cross- ventilation.

Not recommended:

  • Removing historic interior features which play a secondary energy conserving role.

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5) Mechanical systems

Improve energy efficiency of existing mechanical systems by installing insulation in attics and basements.

Not recommended:

  • Replacing existing mechanical systems that could be repaired for continued use.

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6) Building site

Retain plant materials, trees, and landscape features, especially those which perform passive solar energy functions such as sun shading and wind breaks.

Not recommended:

Removing plant materials, trees, and landscape features, that perform passive solar energy functions.

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7) Setting (district or neighborhood)

Maintain those existing landscape features which moderate the effects of the climate on the setting, such as deciduous trees, evergreen wind-blocks, and lakes or ponds.

Not recommended:

  • Stripping the setting of landscape features and land forms so that effects of the wind, rain, and sun result in accelerated deterioration of the historic building.

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8) New additions to historic buildings

Place a new addition that may be necessary to increase energy efficiency on non-character-defining elevations.

Not recommended:

  • Designing a new addition which obscures, damages, or destroys character-defining features.

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