sustainable townhouse primer
Brooklyn’s beautiful old townhouses have great potential to reach an honest “sustainability”. A city of townhouses occupies less space and can be effectively served by mass transit. A townhouse’s shared side walls reduce the structure necessary for each house, and the houses keep each other warm. By contrast, a suburban “net zero” home or an “earthship” of the desert southwest relies upon automobile transport and consumes open space. And these old homes are beautiful structures that have already been built. Their preservation carries forward irreplaceable qualities of historic architecture that cannot be built again today. With care, these houses have the potential to be at once the forward-looking houses of the future and the best of the past… a poetry of past and future combined...
This text has been written to accompany the brochure text for the 2009 Historic Prospect Heights House Tour. The brochure text is in bold/italics, with additional information added after each section. Photos of the houses on the tour by Tracy Collins can be found here.
Looking to the Future:Creating Sustainable Homes
With Prospect Heights’ historic designation officially in place, the future of the neighborhood’s historic townhouses and apartments is now assured. To celebrate this milestone while keeping an eye to the future, the 2009 Prospect Heights House Tour is pleased to highlight the ways in which historic homes can become models of sustainability.
Since buildings are the largest consumers of energy in the United States, we must find ways to reduce energy use within existing structures if we hope to limit our overall energy consumption. Included below is a list of “first steps” that homeowners can take to improve efficiency and costs. Some of these measures will be found in homes on the tour, while others may be less familiar. Importantly, none of these methods diminish the qualities that make historic homes so worth preserving. These starting points simply correct some of their less desirable aspects.
How many property owners are willing to knock down their buildings and start over? The value of incremental gains made by an occasional new high-tech skyscraper are inspirational: clearly our existing building stock must be upgraded.
The ability to live car-free in much of NYC with a very high quality of life must be credited for its potential sustainability, and this is due at least in part to our density. Los Angeles is an obvious example of the difficulty of serving suburban densities, but even in “eco-friendly” cities like Portland, OR, it is extremely difficult to live car-free.
Buildings account for the largest portion of U.S. energy use – 40% for residential and commercial combined, compared to 28% for transportation and 32% for industry.
• Reduce High Heating Bills
Simple home weatherization reduces the drafts that are common in old houses and rapidly pays off in energy savings. Retrofit insulation improves thermal resistance (stopping heat flow from inside to outside and vice versa) for further savings and comfort.
Heating uses by far the most energy in a home, and the performance of your home’s “envelope” – any wall, roof, or floor that separates inside from outside – is the greatest factor in how much heating is used. Investments in upgrading your building’s envelope usually net the greatest return in energy savings from an inevitably limited home-improvement budget. Usually it makes no sense to make a large expenditure on an expensive new boiler or solar panel system if they are supplying energy into an outdated, drafty, 100-year-old container. The performance of your home’s envelope is determined by its draftiness, and its thermal resistance:
Of the possible envelope upgrades, the modest cost of having a weatherization contractor seal air drafts is the single most effective thing that can be done. Air leaks around windows and doors, but also through solid-looking walls at hidden cracks between walls and foundations, windows and bricks, around plumbing pipes, etc. That leaked air is the source of much of the house’s heating demand. A weatherization contractor seals these leaks and confirms the performance achieved with a blower door test.
Thermal Resistance (“R-Value”):
Brick and stone are poor insulators, and the inner, wooden portion of masonry exterior walls were not insulated. Retrofit insulation, usually cellulose or foam, can be injected through small holes which are readily patched into the cavities in the wooden “furring”. These insulations have superior thermal performance and simultaneously reduce air leakage. Conventional pink batt insulation performs poorly, is outdated, and should be avoided as it prevents better materials from being installed later.
Window replacement is costly, and investments are usually most effectively directed first into weatherization, then insulation and then into storm windows.
As a home becomes “tighter”, poor ventilation practices become less tolerable. Care should be taken to insure moist air is removed from bathrooms and kitchens and combustion gasses from mechanical equipment. Fear of poor indoor air is not a reason to perpetuate outdated and sloppy construction practices.
If you are installing a new heating system, the added cost for equipment which allows different parts of the house to be heated different amounts increases both comfort and energy savings, enabling the equipment to capture the efficiency of supplying less heat to naturally warmer areas like a kitchen or south-facing room, and allowing unused areas to be heated less. Hydronic (hot water) heat in the floor is comfortable but no more efficient than hydronic radiators, which do not require removal of original floor or ceiling finishes. Remove old inefficient steam systems.
• Let the Light In
Townhouses can be very dark but the possibility of more light is always available over the stairs. While skylights receive most of their sunlight in summer when its heat is unwanted, creating a small area of raised roof with south-facing clerestory windows simultaneously saves on heating, cooling and energy use for lighting. Light can also be bounced to interior rooms via sunny windows.
Daylighting opportunities vary from house to house, but even for townhouses that are deep from front-to-back additional light is available through the center of the house at the stairs, especially if renovations allow the floor openings to be enlarged. The typical overhead skylight works against the house’s seasonal needs. The sun is high in the sky in the summer, shining mostly on a building’s roof and East and West walls. This makes the typical stair skylight hot in summer without gaining much warmth in winter. In the winter the sun is low in the sky and south-facing walls receive most of its radiation, with little striking the roof. South-facing clerestory windows better match seasonal needs to the position of the sun, admitting sunlight in winter but only reflected daylight in summer.
For houses with bright South-facing front or back windows, sunlight can be bounced deep into the house from white-painted windowsills or lightshelves. This strategy works especially well for houses with a short front-to-back depth, as in Prospect Heights. This light will be distributed much further within the house if the interior paints and finishes, especially the ceiling, are light in color, and can reach interior rooms if transom windows are installed high into interior partition walls.
• Use Less Air Conditioning
Silver roof paint is an excellent way to keep the top floor of a brownstone cool as it costs pennies per square foot and effectively reflects the summer sun. Exterior sunshades on east and west-facing windows efficiently block hot sunbeams before they enter the building and are Landmarks approved. Other improvements in comfort and savings can come from a zoned A/C system or ceiling fans.
As the days become longer in the summer the sun rises further and further east, and sets further and further west. This means that in the summer, the building walls which receive the most solar radiation are East and West-facing, and unshaded windows in these walls are the source of most unwanted heat. (South-facing windows receive relatively little sun). Interior shades accomplish little: once sunlight has passed through the glass its heat is trapped. Exterior sunshades block the rays outside.
While the top floor can be quite hot the basement or even first floors can be much cooler: if you are installing a new central air conditioning system, like for a new heating system, the extra cost for a system that can cool differing rooms separately is a cost-effective and comfortable added expense.
• Save Water
Installing dual-flush toilets as well as rain barrels at roof downspouts for watering plants saves energy that would be spent creating and transporting potable water. If you are renovating, a plumbing recirculation loop or on-demand water heater located near the fixtures overcomes the problem of running the tap on the top floor while waiting for hot water. You will save twofold: once for the energy to heat the water, and again for the water itself.
Though it may not seem so in our climate, water is a natural resource with conservation concerns like any other, and there is considerable energy embodied in creating and transporting potable water, and then cleaning it once it is soiled.
Dual-flush toilets and rain barrels are virtually painless measures which also save twice: less high-value potable water is used but also less waste water must be sanitized.
Install low-flow showerheads, or, at minimum, avoid the high-flow “rainshower” type heads. If you are interested in going further with water conservation, undercounter greywater systems are available which filter used water from the bathroom sink and put it into the toilet for flushing.
• Use Green Materials
Though it’s not easy to evaluate “green” building materials, there are many environmentally sound choices that have historic precedents. Wood is renewable, and metal can be recycled many times. Paying extra for FSC-Certified wood products offers the best assurance that a viable forest ecosystem will be left after your trees’ harvest. Avoid plastics. These petroleum-derived materials are non-renewable, poorly recyclable and their polymers are man-made introductions to the biosphere that will be around for ages.
Accurately evaluating the environmental impact for just one of the thousands of construction materials used in a home would require a life-cycle analysis to evaluate issues such as energy used for extraction, manufacture, transport and installation, durability, recyclability, and renewability of the raw material. The environmental impact of a single standardized component like a wood 2x4 will vary depending upon where it is manufactured! This kind of analysis is beyond the means of anyone other than large organizations with the significant resources necessary to hire the specialty firms that can undertake such analyses.
We are left making sensible, educated guesses, the value of which are often to drive markets to a greater valuing of sustainability and manufacturers to greater accountability, as much as to directly reduce environmental impact by our selections.
Many of the least toxic and most environmental finish materials eschew contemporary petroleum-based products and return to earlier finishing methods contemporary to these old houses: oiled finishes, plasters, and milk-based paints are three examples.
At minimum, use low-VOC paints and water-based polyurethane. Their cost premium is modest and you will simultaneously improve interior air quality.
Plastic polymers never biodegrade, only break down into smaller and smaller pieces. They will be with us forever.
• Conserve Electricity
Many of the buildings in Prospect Heights date to the invention of the incandescent light bulb. Installing the new compact fluorescents is the single easiest way to save electricity. After all, do you still park your old Model T in front of your home? Because a refrigerator is always running, replacing this one appliance with an energy-efficient model will lower your electricity bill significantly over time.
As current legislation in other countries suggests, there is no reason for conventional bulbs to exist any longer. Newer halogen technology looks better but is no more efficient. CFL’s use approximately one-third the electricity. Even better than screw-in retrofit CFL’s are fixtures designed for compact fluorescent “bulbs”, where the lamp is separated from the ballast and can be replaced independently. Another advantage of fixtures designed for CFL’s is dimmability. Retrofit CFL “bulbs” are still poorly dimmable, while fluorescent fixtures have long been available in fully dimmable versions. Even newer for residential use are LED lights which use remarkable little energy - far less even than CFLs. However the light quality from the still-rapidly-developing LED technology is less pleasing than CFL or incandescent.
• Going Further
This ‘primer’ only hints at the vast potential of these old buildings. The inherent efficiency of a townhouse, the fact that they are already built, and Brooklyn’s mass transit options gives us a unique potential to reach a level of sustainability beyond that of a detached suburban “net zero” house. Further improvements can include heating from the sun and cooling via wind without use of mechanical equipment; making power onsite; pursuing sustainable materials and energy efficiency more rigorously; even growing vegetables on the roof. In sum, these houses have the potential to combine the best of the past and future.
For those who are interested, reaching to make a historic townhouse honestly “sustainable” requires additional measures:
Passive heating and cooling strategies:
These measures make modifications to the building to utilize naturally-occurring opportunities in our climate, without mechanical equipment. They all require some degree of renovation. Passive modifications might include making the transom and clerestory windows mentioned above for daylighting operable, which allows hot air to rise and exit the house by convection. This can make more days of the year comfortable without mechanical cooling. If the back of the house faces south with good exposure it is possible to enlarge the windows and exploit more of the sun’s heat in winter. Once your house is made “tight” you will need to introduce controlled air for ventilation. This air can be pre-cooled in summer and pre-warmed in winter by passing it through tubes in the ground, which stays a consistent temperature year-round.
Mechanical equipment can be added to extract energy from the same climatic opportunities to supply the house’s heating, cooling, lighting, and electric systems. These include photovoltaic solar (electricity), thermal solar (hot water), ground-source (“geothermal”) heat pumps, and potentially small wind generators. The payback period for all of these systems can be substantial. They should be selected as part of a larger sustainability goal, not with the expectation that they will rapidly pay for themselves or that they will offset all of the house’s energy needs. They should be considered only after they have been weighed with simpler measures which likely net a greater environmental gain dollar-for-dollar.
Of these, photovoltaic and solar-thermal are well proven. The electric output of PV peaks in the summer when electrical demand also peaks. Because electricity is generated at the point of use the “line loss” suffered in transmission from the power plant is additionally saved. Solar thermal is efficient but misaligned to the seasons as a source of heating, as it captures less energy in the winter and more in the summer. Geothermal heat pumps are a large investment with relatively unproven returns, and as a prototype to be used by every home in the city it is unknown what the impact of changing the groundwater temperature may be. Consider that only a few years ago dumping trash into the oceans was acceptable practice because they too seemed infinitely capable of absorbing our waste. Building-mounted wind turbines produce very little power and can cause unwanted building vibration and should be carefully evaluated.
Forest Stewardship Council Certified wood products were mentioned above, but are worth mentioning again. These can include framing lumber, siding, decking, interior flooring, cabinetry, and furniture. The FSC certification is the best means available to be confident that a viable forest ecosystem is left behind after the tree’s harvest, and as an independent third party they can be held accountable for flaws in their certification more than a manufacturer can be. This certification can come at a significant cost premium, which reflects how unsustainable typical forestry practices are. For those who are interested, there are now innumerable opportunities to make selections from the large, attractive, and ever-increasing selection of recycled, rapidly-renewing, low-toxicity, salvaged, locally-produced and otherwise “green” building materials.
A green roof can be a wonderful aesthetic amenity which, when combined with a roof deck, allows a homeowner to occupy the most beautiful and least utilized open space in the city: the roofscape. A green roof has the potential to simultaneously improve the roof’s insulating quality and reduce stormwater runoff into the sewer, however these qualities are directly related to soil depth, which is in turn limited by the structural capacity of the roof - townhouse roofs typically require structural reinforcement for deep soils, lush plantings, significant water retention, and large improvements in roof insulation. But the poetic promise is enticing – the promise of enjoying the skydome while growing vegetables on the roof and providing habitat for birds and insects holds the promise of a paradigm shift in the way we consider as separate our built and natural environments. As with renewable energy systems, green roofs should be selected as part of a larger sustainability goal, not necessarily for their insulating or air-improving qualities, and their cost should be evaluated along with simpler measures which will likely net greater energy and water savings.
Greater Energy Conservation:
Greater energy conservation forces examination of every item in the home for power usage. This is becoming increasingly challenging as manufacturers add electronic extras to everything from appliances to light switches to phone charges to children’s toys. This outdated attitude assumes that energy is free and without environmental impact – this is not the case. These tiny draws, along with the increasing use of personal electronics, add up – overall home energy use has been steadily increasing. Trying to reduce forces a tedious scrutinization of a myriad of tiny items. Plugging electronics into power strips with on/off switches is relatively painless way to eliminate standby and vampire power usage, but electronic extras in items like appliances pose a problem. When you are renovating there is the opportunity to attempt to eliminate some of these unnecessary extras. Insist that every piece of mechanical equipment be evaluated for energy efficiency. Energy Star labels for items like bath and kitchen fans provide a readily accessible baseline standard. Pay attention for tiny lights on smoke and CO2 detectors, light switches and outlets. Try to eliminate clocks on appliances, etc.