Story at a glance:
- Retrofitting historic buildings with sustainable technologies is a careful balancing act, one that requires architects to find a happy medium between green solutions and the preservation of historic character.
- Making reversible and minimally invasive upgrades—like installing efficient lighting controls or adding secondary storm windows—to a building’s systems and assemblies can help improve energy efficiency without compromising historic value.
- When installing features like solar panels and green roofs, care should be taken to ensure they are hidden from view of the main elevation to avoid detracting from a building’s historic character.
From a material and resource use standpoint, the most sustainable building is often the one that already exists. Instead of tearing down existing building stock, developers and architects are increasingly choosing to adapt, renovate, and retrofit buildings to better suit contemporary needs and deliver improved sustainability.
Retrofitting existing structures with energy-efficient technologies—like high performance interior and exterior insulation, triple-glazed windows, high-efficiency HVAC systems, et cetera—can decrease energy usage by an average of 40%, with deep energy retrofits potentially slashing energy consumption by as much as 60%.
Retrofitting a historically significant building, however, isn’t as simple as your common retrofit project. Many of the energy-efficient envelope upgrades recommended by the DOE, for example, are considered too invasive or damaging to a building’s historic value. Balancing the green solutions of today with historic preservationist ideologies can be challenging, but it isn’t impossible. Here are five tips for retrofitting historic buildings with sustainable technologies.
1. Conduct an Energy Audit to Identify the Least Invasive Solutions
Energy modeling simulations helped inform Cushing Terrell’s renovation of the historic Romney Hall building on MSU’s campus. Photo by Karl Neumann
Before the retrofit of a historic building is planned or carried out, it is imperative that an energy audit be conducted to evaluate the structure’s current performance and identify any energy efficiency issues. A comprehensive energy audit typically includes a thorough visual inspection of the building’s envelope, systems, and appliances; a blower door test to measure air infiltration; thermographic scan to identify thermal bridges and areas of heat loss; duct tightness tests; and even a utility bill analysis to inspect energy use patterns.
The information gleaned from an energy audit helps inform the scope and types of upgrades necessary to effectively reduce energy consumption and improve indoor environmental quality. Consulting a preservationist regarding the results of the audit can be extremely beneficial for determining the least invasive methods for addressing energy problem areas.
In a similar vein, energy modeling simulations can be used to help guide upgrades to energy efficiency. Cushing Terrell, for example, utilized energy models during their renovation of MSU’s historic Romney Hall to inform design decisions that ultimately improved the building’s energy performance by 40.9% compared to a building designed to meet minimum code standards.
2. Opt for Storm Windows Over Window Replacement
When retrofitting MSU’s historic Romney Hall, Cushing Terrell installed 42 secondary storm windows to help improve existing window efficiency. Photo by Karl Neumann
On average heat lost and gained through modern double-glazed windows accounts for roughly 25 to 30% of a building’s heating and cooling energy; this energy waste occurs as a result of air leaks and heat transfer through the glass itself as well as the window frame. Historic buildings may lose even more energy if they possess uninsulated, single-pane windows—as is common in most buildings over 60 years old.
Because historic property renovations emphasize preservation over replacement, however, it is not recommended that new double- or triple-pane low-emissivity windows be installed, especially if existing windows are functional or easily repaired; instead, architects are encouraged to prioritize the installation of interior storm windows/secondary windows. Storm windows are separate window units consisting of a single pane of glass installed on the inside of existing windows—combined, the two windows function similarly to a modern insulated window. Indeed, a 2002 study conducted by Lawrence Berkeley National Laboratory found that installing storm windows over historic windows results in a similar thermal performance to that of new low-E vinyl windows.
When choosing secondary windows, it is important to ensure that the location of elements like mullions and rails match those in the historic windows to minimize their impact on the building’s visual appearance. Care should also be exercised when installing storm windows to prevent damaging existing window frames.
In the event that historically inaccurate windows were installed at some point in the building’s past, or if the original windows are missing or damaged beyond repair, modern insulated windows are an acceptable solution, provided they are accurate or near-accurate replicas of the original windows.
3. Keep Solar Panels Out of Sight
When retrofitting historic buildings with sustainable technologies like solar panels, it is recommended that they be installed in a location that is not visible from the public right of way at the primary elevation to avoid disturbing the site’s historic character. Photo courtesy of HEAPY
Reducing energy consumption is key to improving the overall sustainability of historic buildings, but integrating renewable energy technologies is also a crucial step in decarbonizing the built environment. Unfortunately, features like solar panels can significantly detract from an existing structure’s historic value, creating a jarring contrast between old and modern technologies.
For this reason integration of solar technologies should only be considered after making all other appropriate energy-efficient upgrades; once that is completed, design teams can begin assessing whether a solar array may be installed without compromising the historic character of the building and surrounding area.
As a general rule, this means determining whether it is possible to place solar panels in a location that is hidden from view—when observed from the public right of way at the primary elevation, that is—while still allowing for their efficient operation and performance. It is recommended that compatible on-site locations, additions, and nearby non-historic structures be prioritized before immediately considering installation on the historic building in question.
If site conditions require that solar panels be installed on the building itself, they should only be installed on secondary locations that cannot be seen from a building’s street-facing facades and/or on flat-topped roofs with parapet walls that prevent the panels from being seen from below.
In the event that site conditions or a building’s design and layout make it functionally impossible for solar panels to be hidden from view or would require that materials be removed/roof slope be altered for installation, a solar array should be forgone in favor of other technologies and treatments.
4. Minimize Green Roof Visibility
This green roof on Chicago’s City Hall is considered an appropriate example of retrofitting historic buildings with sustainable technologies as it is not visible from the public right of way at the primary elevation. Photo courtesy of Sika Sarnafil
Adding a green roof to a commercial or residential building comes with a host of benefits that range from improved stormwater mitigation and increased biodiversity to reduced solar heat gain and longer roof life expectancy—and as long as site conditions allow, green roofs can be installed with minimal difficulty on historic buildings.
Similar to solar panels, the most important factor to consider when deciding whether to install a green roof on a historic property is visibility. Green roofs installed as part of a historic retrofit project should not be visible when viewed from the public right of way at the primary elevation—a consideration that limits their applicability primarily to urban properties with flat roofs, particularly those ringed by parapet walls.
Plant species also play a role in preventing green roofs from infringing on a property’s historic character; vegetation must be drought resistant to reduce irrigation requirements and should be appropriately-scaled so as not to be visible from the street level. It is for these reasons that native sedums are typically recommended for historic green roof retrofits, as they are extremely low-maintenance succulents that generally only grow to heights of 2 to 5 inches.
And as with any green roof retrofit, it’s important to verify whether the existing roof can safely support the added weight as is without suffering damage or if improvements to the building’s structural capacity are required. If it is determined that structural improvements must be made, it is crucial that they be done in a sensitive manner that does not detract from the structure’s historic value.
5. Improve Lighting with LEDs & Sensor Technology
Lázaro Rosa-Violán and MG2 added energy-efficient LED lighting during their renovation of the historic Fairmont Olympic Hotel. Photo courtesy of Fairmont Olympic Hotel
One of the easiest and least invasive ways to improve energy efficiency in historic buildings is to replace outdated halogen, incandescent, and fluorescent bulbs with LEDs. On average LEDs are 40 to 90% more efficient than traditional light sources and produce little to no heat, reducing the risk of damage to historic materials.
Many LED manufacturers also offer bulbs that are compatible with fixtures originally designed for halogen, incandescent, and/or fluorescent bulbs, meaning that existing historic light fixtures need not be replaced during a retrofit unless they are damaged beyond repair.
In addition to LEDs, upgrading historic buildings’ lighting controls with sensor technology can help to greatly reduce their lighting-related energy use. An interior lighting system equipped with automated daylight sensors, for example, is estimated to deliver anywhere from a 20 to 60% increase in energy savings.
