When you are planning to rehabilitate your historic house or commercial building, you may want to consider ways to improve your building’s energy efficiency. Your historic house or building is already more energy efficient than many modern buildings, but there are several ways that you can retrofit your structure to save on energy costs.

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Installing a window awning can greatly reduce the solar heat gain through south and west facing windows; thus reducing your air conditioning costs. Source: WHS - State Historic Preservation Office.

Maintain the Existing Energy-Efficient Features

Before electricity was available, buildings were designed to capitalize on natural sources of lighting, heating and ventilation. You can maintain the energy efficiency of your historic home or commercial building by maintaining the original energy efficient features of your structure. Some elements of older buildings that contribute to their excellent energy efficiency include the following:

• Thick, heat-retaining masonry walls made of stone or brick
• High floor-to-ceiling height to circulate air 
• Operable double-hung sash or casement windows with transoms to circulate air.
• Storm windows or shutters added for additional energy efficiency
• Operable transoms over doors to aid in natural air circulation
• Prism glass transoms to refract (bounce) light farther back into the interior, reducing the need for electrical lighting
• Operable awnings to block direct sunlight and gain heat

Conduct an Energy Audit

Before you make energy upgrades, you should have an energy audit completed on your house or building. An energy audit is a study of your building’s energy use and equipment. The audit will determine how and where energy is escaping from your building. An energy auditor will inspect your building’s lighting, air conditioning, heating and ventilation equipment and controls, air compressors, water-consuming features and anything else that is using energy. The auditor will develop a list of energy conservation measures that you could implement to reduce energy usage and costs in your building.

Be aware that an energy auditor will not consider any best practices to preserve the historic character of your building. You should use your own judgment to balance energy conservation suggestions with historic preservation practices. Some energy-efficiency measures may take decades to pay for themselves, while others will start paying for themselves within months. A program specific to Wisconsin that can help businesses save energy and money is the Focus on Energy Program.

Upgrade the Mechanical Systems

If the original mechanical components of your house or building are missing or no longer functional, you will need to install modern systems in a visually unobtrusive manner. Ensure that you are providing adequate structural support for new mechanical equipment, and make sure it does not create excessive moisture that could deteriorate your historic materials.

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Installing mechanical equipment on the roof of an historic building is acceptable as long as it is not visible from the public right-of-way. Source: WHS - State Historic Preservation Office

If you need to install a new heating, ventilation and cooling (HVAC) system, you should design it to cause the least possible alteration to your building's floor plan and the least damage to your historic building materials. HVAC units are the better choice over window air-conditioning units because HVAC units are more efficient and may have less of a visual impact than window units.

Add your new HVAC system in a location where it will not be readily visible from the public right-of-way. Typically HVAC systems are added on the roof and set behind parapet walls so that they are not visible. Another appropriate location is at the rear of your building. If you place an HVAC unit on a rear façade, it should be screened with fencing, lattice or landscaping. The extent of the new system’s visibility should depend on your building’s historical identity. Here are two examples:

• If historically your building was a finished space like a merchant store, then install as much of the ductwork or cables as possible within wall cavities, closets, floors, ceilings or newly constructed soffits.
• If the historical identity of your building is an unfinished space, such as an industrial building or a blacksmith shop, then consider using exposed spiral ducts to respect the unfinished identity of your building.

Best Practices

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Heat loss through an uninsulated roof is significant. Adding insulation to the floor of an attic helps maintain the heat within the house and also a cold roof (prevents ice damming). Source: Phil Thomason.

Use the following best practices in your historic building to make it more energy-efficient.

• Conduct an energy audit of your house or building. Use an energy audit to identify methods to make your historic house or building more energy efficient and provide long-term cost savings. Wisconsin’s state government and local utilities have many programs to assist building owners with energy audits.
• Weatherize your doors and windows. Tighten up leaky windows and doors in your historic house or building by adding weatherstripping and caulking any open cracks or joints. Use appropriate colors that complement the historic character of your building. 
• Add insulation to your attic. Attic insulation may provide you with the best cost-savings and payback than any other retrofit. The most common attic insulation materials include cellulose, mineral wool, fiberglass and vermiculite.
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  Agricultural Dean's House, 1896

  Madison, Wisconsin. Installing a high quality storm window at either the interior or exterior of original wood windows greatly improves the windows' energy efficiency. Source: Photographer Mark Fay. View the property record: AHI 16711

  Add storm windows. Instead of replacing your original wood or metal windows, increase their energy efficiency by adding storm windows. Storm windows will reduce thermal transmission through your windows and will not affect the historic character of your house or building. You can paint storm windows with appropriate colors or purchase storm windows with a baked-enamel finish that is compatible with the color of your window trim. Storm windows will be effective regardless of whether they are installed on the interior or exterior of the original frame. However, keep in mind that interior storm windows may make your historic windows excessively cold, cause moisture to condense or result in peeling paint and deteriorated wood. Interior storm windows should have sufficient weep holes to allow moisture to escape. 
• Only install replacement windows if your original windows are beyond repair. You should never replace the original windows in your historic house or building unless they are clearly deteriorated, rotted or damaged beyond repair. Your house or building may also have had non-historic windows added within the past 50 years. If these added windows are single pane, you may wish to install new thermal pane windows that are designed to resemble historic wood or metal windows.
• Add thermal pane film to your windows. Another option you can consider for your historic wood or metal windows is thermal (or solar) pane film, which allows visible light to enter windows but blocks ultraviolet (UV) light. This self-adhesive polyester film traps beneficial heat inside a building and reduces solar heat gain. However, some thermal pane film may be too dark or thick to maintain the historic appearance of your window. The film should not be so dark that it looks like tinted glass nor so clear that your glass does not look typical for historic windows. Depending on the film you select, you may be able to install the film yourself or you may need to hire a professional.
• Replace your HVAC units. If your building has HVAC units that are more than 10 to 20 years old, consider replacing these units with Energy Star®-rated appliances. An upgraded HVAC unit will have the most impact on your building’s energy efficiency.
• Place heating and cooling equipment in locations that are not readily visible. Place modern heating and cooling units on your rooftop or at side and rear locations that are not readily visible from public view. You can also screen these units with landscaping and fencing. 
• Replace your incandescent light bulbs. Replace your incandescent light bulbs with compact fluorescent light (CFL) bulbs.