Older buildings often carry a reputation as costly to heat in the winter, inefficient in their overall use of energy and difficult to make substantial energy-saving gains in. When considered across the spectrum of environmental factors, however, retention and adaptive reuse of historic structures is a very “Green” endeavor. If you really want to “go green,” consider finding a historic building for your residence or place of business.

Most historic structures are located within walking distance of community favorite amenities, including Bozeman’s Main Street Historic District, the Bozeman Public Library, the Gallagator Trail system, elementary schools and local parks. Proximity to downtown enables walking or biking to these wonderful community assets, thus avoiding the use of carbon-based fuels necessary to power an automobile.

Continued use of the historic central core slows the expansion of the City’s boundaries, thus preserving the rich agricultural fields of the Gallatin Valley. In turn, utilization of existing infrastructure prevents expansion, usually done by carbon-fuel intensive means, of the city’s roads, sewer, water and other utility lines.

Historic buildings often respond more appropriately to their environment. A century ago builders used site considerations like landscaping and building orientation and design in order to take advantage of sunshine in the winter and shade in the summer to regulate interior temperatures. For example, many of Bozeman’s historic residential districts are characterized by deciduous trees strategically planted to the south or west in order to shade the building in the summer. The trees lose their leaves in winter, thus exposing the building to passive solar gain.

Exterior design features of historic buildings reflect Montana’s varied weather patterns. The popular combination of white paint with black trim on residential structures kept buildings cool in the summer, while the black trim melted snow and warmed the windowsill in the winter. Storm windows, made to fit each individual window, offer a second layer of glass and, when properly constructed and maintained, seal along the trim, creating an airlock to buffer the cold exterior from the warmer interior temperatures.

Porches in Bozeman’s historic residential neighborhoods are another unique exterior design adaptation to the climate. About a third of the Craftsman-style residences constructed in the historic core incorporate an “enclosed” half-wall as a porch railing. During winter months, storm windows added between the half wall and the porch header, in addition to a storm door; create a three-season room which acts as a buffer between the coldest of temperatures and the interior of the residence. Removal of the windows enables a temperate exterior sitting area through the warm summer months.

Historic commercial buildings incorporated low-technology systems to provide interior air movement, light and heat. Ventilation during the summer months was achieved through thermal convection; essentially, the idea that hot air rises.  Starting on the ground floor, cooler air entered a building through an opened doorway or window. Operable transom windows, usually located above the entry door were opened in the summer months, enabling the hot air trapped near the ceiling of the room to escape. In multi-story commercial buildings, transom windows above doors located along interior corridors enabled warmer air to leave the rooms and travel up a stairwell. The design of these buildings often incorporated lanterns, a small windowed superstructure crowing the roof. The windows in the lanterns acted as a skylight, providing much-needed lighting of the stairwell, and could be opened in the summer to release heat rising through convection, thus promoting air circulation through the building.

Embodied energy is another important consideration when discussing the energy efficiency of historic buildings. In this usage, embodied energy calculates the energy already spent to extract, process, manufacture, transport and install building materials in an existing building. Many of Bozeman’s historic structures date to the early 20th century and incorporate wood or brick materials.  For example, a summary of the embodied energy of a historic Craftsman residence should summarize the resources used to log old-growth lumber, transport the logs to a mill, mill the logs into dimensioned lumber, and transport the dimensioned lumber, often by railroad, to a local lumberyard for retail sale. Once purchased, the lumber was transported to a building site, often by inefficient means. In this manner, we’ve heavily invested energy resources in our existing buildings.

The perceived inefficiency of historic buildings is often used as an argument for replacing the structure with a newer model. Studies have shown, however, that after incorporating the fossil fuels used in construction of a building, a new structure doesn’t actually start saving energy for about 40 years. If the project required demolition of a historic building, the new building will not break even on energy savings for 65 years, given the energy used in demolition and disposal of the original structure.

Energy-saving improvements to older buildings can be accomplished through a variety of means. Owners find the biggest “bang for their buck” in upgrading the insulation in a building’s roofing system or around the building’s foundation. Like putting a hat and socks on a house, these improvements usually have less than a five year payback period. Installation of storm windows and doors, as well as caulking around all exterior openings, further retains interior heat. In terms of cost vs. energy gain, replacing historic windows is actually a poor investment; new windows have about a 25 year payback period if the highest quality windows are installed.

An energy audit performed by the local utility company or private contractor should be the first step when considering improvements in energy-efficiency for a structure. The data created by a survey of the building’s energy performance usually includes an evaluation of the building’s mechanical systems, window and door openings through walls, and site considerations. The recommendations made by an energy audit should be a starting point in prioritizing reinvestment in the energy-saving rehabilitation of an existing building.

Courtney Kramer is a proud graduate of MSU’s History Department and serves as the City of Bozeman’s Historic Preservation Officer. She may be contacted at the City Planning Office, 406-582-2260 or via email at ckramer@bozeman.net. More information about Bozeman’s historic districts is available at www.preservebozeman.org