Sustainability and Historic Preservation
2013 - by Audrey Holt, Previous Project Design Assistant
Today, the word "sustainability" has everyone’s attention. From recycling, to hybrid cars, to energy efficient "green building," it is a topic that is at the forefront of the nation’s consciousness. So what is sustainability and how does it relate to the historic buildings in your downtown? Sustainability is defined as “Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” ” from the World Commission on Environment and Development’s report, Our Common Future (Oxford: Oxford University Press, 1987—also known as the Brundtland report). It can be said that being sustainable is to be a good steward.
Many think that "green building" and "sustainability" are synonymous. This is not the case. Green buildings are a part of, but are in no way the only portion of, the wider sustainability movement. Sustainability includes green building concepts, but within a broader context. At the most basic level, when a new building is constructed, energy is used and when an old building is preserved, energy is saved. As noted by Donovan Rypkema, principal of PlaceEconomics (a private sector firm with extensive experience in the measurement of the economic impacts of historic preservation), "it has been estimated that the energy consumed in the construction of a building is 15-30 times the annual energy use of that building." A newly constructed mixed-use building takes approximately 42-80 years to overcome the negative environmental impact of its construction.
In addition, the materials in a new building are usually more consumptive of energy than the materials used in historic buildings. Brick, plaster, concrete, and timber used in historic buildings consume less energy, as they are non-toxic, durable materials with long life cycles that are able to be repaired and reused and that were often locally produced and assembled. On the other hand, most new buildings are constructed from the most energy consumptive materials, such as plastic, steel, vinyl, and aluminum. For example, vinyl is toxic to produce and dispose of, has a short life span, is impossible to repair, and once mass produced it must be transported long distances.
Embodied Energy
Embodied energy is the term for the total energy expended in the creation of a building and its materials and parts. When a historic building is torn down and thrown away, all of the energy put into the creation of that building is thrown away and lost forever. Embodied energy savings increase dramatically once a building’s life stretches over 50 years. If a building is over 100 years old, you can use 25% more energy every single year after that and still have less lifetime energy use than a building that lasts only 40 years. The Environmental Protection Agency has projected that 27% of all existing buildings will be replaced between 2000-2030, so many buildings being built today won’t even last 40 years.
If you do the math, assuming a typical downtown building is 25’ wide and 100-140’ deep - if a single small building like this is sent to a landfill, the entire positive environmental impact from the last 1.3 million aluminum cans that were recycled is wiped away. This same building is roughly equal to the amount of energy embodied in 3,900 gallons of gasoline – enough to keep the average American driving for more than eight years. You can figure the embodied energy, demolition energy, compare embodied energy to gallons of gas, and even do a complete teardown calculation for a specific building at http://www.thegreenestbuilding.org/
Studies by the Energy Research and Development Administration show that the buildings with the poorest energy efficiency are actually those built between 1940 and 1975. According to the quadrennial study of buildings in the U.S. by the Department of Energy (CBECS), buildings built before 1960 use less energy per square foot, on average, than buildings built since then. A Department of Energy study shows commercial buildings built prior to 1920 are as energy efficient as most buildings constructed after 2000. Before implementing any energy conservation measures to enhance the sustainability of a historic building, the existing energy-efficient characteristics of the building should be assessed.
Assessment
Historic buildings possess many existing energy-efficient characteristics that should first be examined before implementing any new energy conservation measures. From the National Park Service and the U.S. Department of the Interior’s Preservation Brief 3: Improving Energy Efficiency in Historic Buildings, “Buildings are more than the sum of their individual components. The design, materials, type of construction, size, shape, site orientation, surrounding landscape, and climate all play a part in how buildings perform… The key is to understand and identify the existing energy efficient aspects of the historic building and how they function, as well as to understand and identify its character-defining features to ensure they are preserved.” The inherently energy efficient qualities of historic buildings include (but are not limited to!):
Location:
Historic buildings are typically centrally located. This increases walkability, utilizes existing infrastructure, and preserves green space.
Windows, courtyards and light wells:
These were historically limited to only those necessary to provide natural ventilation and light, which in today’s world helps reduce dependence on energy consumption. Any time the mechanical heating and air conditioning equipment can be turned off and the windows opened for ventilation, energy will be saved.
Relevant to our hot climate, windows were often shaded with features such as roof overhangs, porches, balconies, canopies, awnings, shade trees, interior or exterior shutters, venetian blinds, shades and curtains to reduce heat gain through the windows. In addition, many historic buildings were designed with the living spaces on the second floor to catch breezes and to escape the radiant heat from the earth's surface. This differs from the approach in many modern buildings where the percentage of windows in a wall can be nearly 100%. Windows, historic or not, are poor insulators when compared to walls. In addition, most new buildings are not designed for ventilation. Therefore, historic buildings, where the ratio of glass to wall is often less than 20%, are better energy conservers than most new buildings.
Walls:
Thick masonry walls typical of many historic buildings have inherent thermal characteristics that keep the buildings cooler in the summer and warmer in the winter.
Walls with substantial mass have the advantage of high thermal inertia, which reduces the rate of heat transfer through the wall. This is the reason many older buildings feel cool in the summer without air conditioning.
Floor plans and site orientation:
The floor plan was usually designed to respond to the local climate. Wide, central halls, tall ceilings and large porches all situated to take advantage of prevailing breezes maximize air circulation. Often trees were planted to the south to provide summer shade and maximize sun in winter.
Good preservation practice is often synonymous with sustainability. Sometimes all that is needed to make your historic building more green is to undo inappropriate alterations that have, over the years, reduced its energy efficiency. In most cases undoing such alterations is relatively simple and inexpensive. Such alterations include removing a suspended ceiling, uncovering transom windows, and restoring a storefront to its original configuration.
When attempting to reduce energy expenditures, there are two broad courses of action. Passive measures assure that a building and its existing components function as efficiently as possible without the necessity of making alterations or adding new materials. This is a more ‘DIY’ approach that requires little special skill and usually costs very little money. Preservation retrofitting includes altering the building by making appropriate weatherization measures to improve thermal performance. For these measures it is highly recommended to bring in professionals with preservation expertise. Undertaking passive measures and preservation retrofitting could result in a 50% decrease in energy expenditures in historic buildings.
When attempting to reduce energy expenditures, there are two broad courses of action. Passive measures assure that a building and its existing components function as efficiently as possible without the necessity of making alterations or adding new materials. This is a more ‘DIY’ approach that requires little special skill and usually costs very little money. Preservation retrofitting includes altering the building by making appropriate weatherization measures to improve thermal performance. For these measures it is highly recommended to bring in professionals with preservation expertise. Undertaking passive measures and preservation retrofitting could result in around a 50% decrease in energy expenditures in historic buildings.
Passive measures of increasing energy efficiency should be done first as they are particularly appropriate for historic buildings because they do not necessitate building alterations. Passive climate control measures include: lowering the thermostat in winter and raising it in summer, installing programmable thermostats, controlling the temperature only in those rooms actually being used, establishing climate zones with separate controls, using operable windows, shutters, awnings and vents as originally intended to control interior environment and for ventilation, and using a ceiling fan so that the thermostat can be kept at a higher temperature (If you have a whole-house attic fan, use it!). Basic maintenance of existing units can also increase efficiency, such as having mechanical equipment serviced regularly, and cleaning radiators and forced air registers to ensure proper operation. Electricity can be further reducing by lowering the level of illumination through the number of lights (maximize natural light) and investigating higher efficiency lighting types that can be used in existing fixtures, such as fluorescent bulbs. Simply monitoring occupant behavior in regards to energy use, such as turning lights and hvac off when the building/room is not in use, will help to further increase efficiency. These passive measures can save as much as 30% of the energy used in a building, all with no major expense or alterations. Passive measures make energy sense, common sense, and preservation sense!
Preservation retrofitting is the next course of action in increasing the efficiency of historic buildings. At this point it is recommended to bring in professionals. First, a thorough building investigation of the basic building components of the attic, roof, walls and basement is necessary. Check for insulation to determine the need for additional insulation. Note if there is a vapor barrier. Next, look for sources of air infiltration. Major areas of concern are doors, windows, and where floor and ceiling systems meet the walls. Assess the condition of the exterior wall materials, such as painted wooden siding or brick, as well as the condition of the roof, to determine the weather tightness of the building. In order to fully identify areas of concern, have an energy audit performed. An audit should include thermal imaging, and a blower door test, and it is best done in late fall, winter or early spring when there is a significant temperature difference in the interior and exterior of your building.
Ways to reduce air infiltration:
Substantial energy loss occurs because outside air infiltrates, or escapes, the building through loose windows, doors, and cracks in the outside shell of the building. Reducing air infiltration should be the first priority of a preservation retrofitting plan. The cost is low, little skill is required, and the benefits are substantial. Care should be taken not to reduce infiltration to the point where the building is completely sealed and moisture migration is prevented. Without some infiltration, condensation problems could occur throughout the building. Ways to reduce air infiltration are listed below.
Attic Insulation:
Heat rising through the attic and roof is a major source of energy loss; therefore, adding insulation to the total depth recommended in accessible attic spaces is very effective in saving energy. The most common types of attic insulations are: blankets of fiberglass and mineral wool, blown-in cellulose (boric acid treated only), blowing wool, vermiculite, and blown fiberglass. If flooring is present, or if the attic is heated, the insulation is generally placed between the roof rafters (typically the vapor barrier faces in). If the attic is unheated, insulation is placed between the floor joists (typically the vapor barrier faces down). If the attic floor is inaccessible, or if it is impossible to add insulation along the roof rafters, consider attaching insulation to the ceilings of the rooms immediately below the attic. Install all insulation according to manufacturer’s specifications. Adding attic insulation should not be considered if it causes irreparable damage to historic or architectural spaces or features.
Properly ventilate your attic:
The attic is adequately ventilated when the ventilation square footage equals approximately 1/300 of the attic square footage. Installing a ventilation fan can draw cool air into the area to reduce temperatures. Improving air circulation can prevent mold and mildew growth and structural damage from condensation, whereas a lack of ventilation will cause the insulation to become saturated and lose its thermal effectiveness. Proper attic venting also reduces heat buildup in the hot months, extending the life of roofing, framing, and insulation materials and improving the efficiency of air conditioning units. Investigate if a whole house fan could work to ventilate the usable spaces in your building. These fans, mounted on the attic floor, draw cooler air in through open windows on the lower floors and expel warm air through attic vents. During evening hours these can reduce the need for air conditioning by drawing cool air through the home.
Basement and crawlspace insulation:
Substantial heat is lost through cold basements and crawl spaces; however, adding insulation is complicated because of the excessive moisture that is often present. In crawl spaces and certain unheated basements, the insulation is generally placed between the first floor joists (the ceiling of the basement) with the vapor barrier facing up. Do not staple the insulation in place, because the staples often rust away. Use special anchors developed for insulation in moist areas such as these. In heated basements, or where the basement contains the heating plant (furnace), or where there are exposed water and sewer pipes, insulation should be installed against foundation walls. Begin the insulation within the first floor joists, and proceed down the wall to a point at least 3 feet below the exterior ground level if possible, generally with the vapor barrier facing in. Use either batt or rigid insulation. As is the case with attics, adequate provision must also be made to ventilate unconditioned basement spaces with proper venting and perhaps a vent fan.
Duct and pipe insulation:
Ensure that your heating and cooling ducts are properly sealed. Wrapping insulation around heating and cooling ducts and hot water pipes can improve efficiency. Use insulation which is intended for this use and install it according to manufacturer's recommendations. Note that air conditioning ducts will be cold in the summer, and hence moisture will condense there. Use insulation with the vapor barrier facing out, away from the duct. These measures are inexpensive and have little potential for damage to the historic building.
Storm windows:
Adding a storm window to a properly restored wood window improves the efficiency of the window system and typically results in a window assembly (historic window plus storm window) with an R factor of 1.79. This outperforms most double paned window assemblies (with an air space up to 1/2") which have an R factor of 1.72. If a building has existing storm windows (either wood or metal framed) that are tight fitting and in good working condition, they should be retained. Compare the cost of the storm windows plus installation with the expected cost savings resulting from the increased thermal efficiency. When installing the storm windows, be careful not to damage the historic window frame.
There are both interior and exterior storm windows. Triple track storm windows are exterior storm windows that are recommended over double or single track. In a triple track storm window, the top pane of glass can be lowered and the bottom pane can be raised to not interrupt the intended functioning of a typical double hung window, therefore allowing the windows to still be used for ventilation. These windows are readily available, in numerous sizes, and at a reasonable cost. Generally, custom-made storm windows, of either wood or metal frames, are not cost effective, and would not be recommended in a preservation retrofitting plan.
Interior storm windows can be as thermally effective as exterior storm windows and are less visually intrusive. A disadvantage is that there is high potential for damage to the historic window and sill. With storm windows on the interior, the outer sash (in this case the historic sash) will be cold in the winter, and moisture may condense there. This condensation often collects on the flat surface of the sash or window sill, causing deterioration. If interior storm windows are in place, the potential for moisture deterioration can be lessened by opening (or removing) the storm windows during the mild months, allowing the historic window to dry thoroughly. Ensure installation does not damage the historic sash.
Awnings, canopies and trees:
Historically, these were extensively used to provide shade to keep buildings cooler in the summer. If in place, maintain and take advantage of their energy-saving contribution. Consider adding awnings (term indicates a less permanent structure than canopy) or trees, especiallyto south or west facing facades, as long as installation does not damaging the building or visually impair its architectural character. If trees are desired, select deciduous trees to provide shade in the summer but allow the sun to warm the building in the winter. Plant trees typically no closer than 10 feet to the building to avoid foundation damage. Adding either awnings or shade trees may be expensive, but in hot climates, the benefits can justify the costs.
Efficient heating and cooling units:
Inspect units often and examine the performance of the HVAC system to ensure that it is operating efficiently. Don’t replace a functional and efficient system with one that is marginally more efficient. If replacement is needed, more energy- and cost-efficient HVAC systems are available now than at any point in history. Among some of the newer options are high efficiency ductless units, mini duct systems (less impact on historic spaces and materials), geothermal heat pumps (use the energy and consistent temperature found in the ground, a pond, or well water as a heat source and heat sink), high-efficiency, gas-fired rooftop units (combine the condenser, compressor, and evaporator in a single unit and use pulse combustion), and new energy-efficient boilers (smaller, enabling several small boilers to variably heat different parts of the building based on use).
When considering retrofitting measures, historic building owners should keep in mind that there are no permanent solutions. In the future, it is likely that today’s efficiency standards and available technologies will have changed and a whole new retrofitting plan may be necessary. Be careful to not install new equipment in such a way that its later removal will cause irreversible damage to significant historic materials. Limit retrofitting measures to those that achieve reasonable energy savings, at reasonable costs, with the least intrusion or impact on the character of the building.
Undertaking of the preservation retrofitting measures mentioned above can result in another 20%-30% reduction in energy (added to the up to 30% reduction gained from passive measures).
Things you should not do when attempting to make historic structures more efficient:
Replace historic wood windows. Original windows are a character defining feature. Studies have demonstrated that the energy savings that might be gained by replacing historic windows with new double-glazed windows is inconsequential. Glass, whether single-or double-pane, is a poor insulator. The environmental costs of manufacturing new windows and sending old ones to the landfill are far greater than the benefits to be gained in energy savings.
Wall insulation in a wood structure. This has a high cost for installation and low return since energy loss out the walls is a relatively small percentage of the total, most of which can be attributed to air infiltration that can be addressed by sealing up leaks. There is a very high possibility for damage to historic materials due to the fact that insulation must be kept dry; therefore, needs a vapor barrier and air movement. If not done properly, condensation will damage all wooden components in your wall- your wood siding and framing.
Cavity insulation in a masonry structure. Masonry cavity walls were intended to function as a thermal barrier. The interior and exterior walls function independently in order to slow the transfer of heat or cold between them, with the air cavity acting as a vapor barrier. Masonry walls were designed for condensation to run to the bottom of the wall cavity and drain outside through weep holes. Adding insulation alters the vapor barrier and thermal cushion functions of the air space and allows moisture to become trapped in the wall cavity. This water can then saturate and deteriorate your brick, even causing the moisture to freeze and the brick surface to pop off or spall.
Interior wall insulation. This often requires relocation or destruction of important architectural decoration such as cornices, chair rails or window trims.
Exterior wall insulation (aluminum or vinyl siding). Siding actually covers up potential deterioration issues or insect infestations, as well as damages existing decorative features such as window and door trim, corner boards, cornices and roof trim. It is known to cause a 12% drop in value when installed. Manufacturers claim it reduces long-term maintenance and improve thermal performance when actually it has a high cost of installation compared to little to no increase in thermal performance of the wall and requires wholesale replacement if damaged. You can easily maintain historic wood siding with periodic painting and caulking and you can repair smaller areas of damaged wood siding using an epoxy. In cases of more severe damage, you can replace only the areas that are actually damaged, a much more sustainable practice.