Taking the green exterior beyond energy

An integrated planning process is the key to a green envelope

By Abigail Kelly  

What does “green” mean where a building envelope is concerned? For many facility executives, “energy efficient” is the first answer that comes to mind. They’re right: The exterior plays a critical role in determining a facility’s energy consumption, which is a large part of its overall impact on the environment.

But energy efficiency is not the whole story. Increasingly, designers who strive to build green facilities take into account, along with energy efficiency, the envelope’s impacts on building occupants and on the surrounding environment — be it rural or urban — and the overall life-cycle impacts of the materials involved, including their manufacture, processing and transportation.

There is a lot to be concerned with. And while there are many guidelines and tools available to help with decision-making, even the most environmentally savvy designer will tell you that there are relatively few hard and fast answers.

Green Exterior Basics

An environmentally sound envelope starts with basic architecture.

“Orientation makes a huge difference,” says Tom Nelson, vice president and senior project designer with HOK.

An east-west orientation generally will help mitigate energy consumption by making it easier to minimize western sun exposure — the most difficult in terms of solar heat gain and glare. In addition, it may make sense to minimize window openings on the western side and, instead, to concentrate them on the south side of the facility, where summer sunlight will be less intense and shading can be used to control glare.

Floorplan is also important: Narrower floorplates will allow sunlight to penetrate deeper into the facility, reducing internal lighting requirements and energy demand.

In addition, explains Bill Browning, principal and founder, Rocky Mountain Institute’s Green Development Services, “you generally want the longest facades to be north and south facing. It’s easiest to control the light coming into them.”

Basic design steps like these constitute what Nelson describes as “passive strategies.” For facility executives involved in new construction, these are important strategies to employ when attempting to achieve a green exterior; compared to more technology-reliant strategies involving building-system and materials choices, passive strategies are cheap.

“We can do a fair amount of sustainable design without influencing cost,” says Nelson. “Some of it is just basic architecture and doesn’t cost anything.”

Specifying for Sustainability

When the discussion turns to the specific systems that make up a building’s skin, technology quickly becomes a major factor in determining environmental impact. At this point, choices and cost analyses become more complicated. But the stakes at this stage in the game are high and the decisions important: The products and systems chosen for the exterior of a facility go a long way toward determining how green a building will be.

Just how critical a building’s skin is to its environmental impact varies somewhat with the size and type of building and its intended usage. For example, in skin-dominated buildings — often those under 50,000 square feet — the energy efficiency of the building’s exterior systems and design are critical, so considerable effort goes toward adjusting for heat gain or loss. In larger, load-dominated buildings, the activities inside the facility are often a bigger factor in its overall energy consumption, so the skin characteristics may be less meaningful than the building’s internal systems and design. Factors like these are important to consider when deciding how much of your construction budget to direct toward greening the exterior.

For all facilities, windows have a major impact on environmental friendliness, primarily for their energy efficiency effects. The fenestration options available to today’s specifiers are myriad, and the best choice depends on a combination of variables, including climate; building type, size and usage; and, of course, budget. There are, however, some basic guidelines that will hold true in most applications: Low-e glazing is a baseline rule of thumb for energy efficiency. Multilayer glazing adds additional efficiency, and coatings with appropriate spectral performance characteristics should be chosen based on exposure.

“There are various technologies that can allow you to start controlling heat and light flux across the envelope,” says Browning. “You can get lots of heat and light where you want it, but control the infrared.”

Windows also have a profound effect on both energy efficiency and indoor environmental quality (IEQ) where daylighting is concerned, as effective fenestration can create a better indoor environment while lowering heating and cooling demands. Architecture can lend a hand in this area, as well. A building can be designed to shade windows, allow maximum light penetration, or offer both shaded windows and full daylight.

Roofs and Walls

Roofs also play an important role in the design of a green envelope. “A cool roof can save you 20 to 30 percent on cooling annually,” says David Gibney, sustainable design coordinator, HDR. That translates directly to lower impacts on the environment as a result of reduced energy consumption.

Looking for an Energy Star®-certified roofing system is a good place to start. In addition, consider the roof’s color — white roofs reflect more heat, decreasing the load on the cooling system — and its moisture management properties, as storm water runoff can take a toll on civic infrastructure and the surrounding environment.

Roofs that are literally green, featuring grass, trees and other plants, are becoming more common, and green designers laud them for their shading, insulating and water absorption properties.

The roof is not the only place where green design may be, literally, green. More and more, say architects, plants are a part of environmentally conscious exterior design, and designers often look to Mother Nature to provide facility solutions.

“Landscaping can help with natural shading and with blocking wind,” says Gibney.

“There are plenty of surfaces that can be used for growing things,” says Bill Reed, vice president of integrative design, Natural Logic. “We see living walls and plant screens all becoming more common.”

Last but not least among the major exterior components, external walls also affect a building’s overall environmental impact. Chiefly, say experts, facility executives should be concerned about walls’ moisture performance, as a poorly performing wall can lead to mold and mildew, which are major detriments to IEQ and occupant health.

“If you’ve got stone, brick or a similar exterior façade that is, in effect, permeable, you may want to put a moisture barrier and make sure there is a slot in between the layers to let the moisture escape,” recommends Browning.

In addition, recommends Richelle Schoessler Lynn of LHB, “you need a breathable finish in the interior of the exterior wall in order to avoid mildew.”

Taking the Next Step

Following sound design principles and making informed product choices will stand you in good stead where energy efficiency and IEQ — certainly among the most important factors in an envelope’s overall impact on both the indoor and outdoor environment — are concerned.

Taking the next step toward making the envelope environmentally friendly can be another matter, as a discussion of the true life-cycle impacts of materials gets complicated fast.

Indeed, materials specification is a science unto itself, and it’s one where there are no clear-cut answers.

“It will always come down to tradeoffs and choices,” says Rebecca Foss, an architect and specifier who works with both EcoDesign Resources Inc. and the Center for Sustainable Building Research at the University of Minnesota.

In short, however, the less energy and pollution that is generated over the sum total of a material’s manufacturing, transportation, finishing, installation, and use, the fewer its negative impacts on the environment.

“You have to look at the downstream and upstream implications of your decisions,” says Reed.

For some facility executives, looking closely at the real environmental impact of materials demands a closer look at a broader spectrum of issues. For instance, facility executives might want to consider how much carbon dioxide is generated by shipping stone from across the country or evaluate a product’s recyclability.

“We’re accustomed to looking at basics like durability, ease of maintenance, long-term adaptability and so forth, but now we’re also looking at the total impact of extracting, producing and manufacturing materials,” says Foss.

Integration is Key

So what is the secret to achieving a truly green envelope? The experts agree: an integrated planning process.

“Everybody talks about it,” says Reed, “but few people do it well.”

And the process must be integrated on a number of levels, starting with involving the right combination of decision-makers in the design process.

“Most architects and engineers can bring the right level of expertise to the table,” says David Ejadi, vice president, The Weidt Group. “But things often get short-circuited when owners don’t bring enough of their team to the table. Make sure you get buy-in from as many levels as possible.”

It may also mean integrating budgets and priorities in new ways.

“There are so many cases where architects have designed the envelope to be a daylit building, and then somebody else comes along and blocks the windows or puts in really high partitions because that’s what has always been used and what is in the budget,” says Ejadi.

Furthermore, an integrated approach necessitates looking at building systems in a holistic way. That is, looking at systems not just in terms of how they operate, but how they operate relative to one another.

“People will say, ‘Let’s not use triple-glazed windows because they are too costly,’ ” says John Carmody, director of the Center for Sustainable Building Research at the University of Minnesota. “But in some cases owners have been able to eliminate perimeter heating and downsize mechanical systems enough to pay for the windows.”

Also key is integrating the design process from the beginning. If daylighting and heat gain are considered in the design of the structure, for instance, it may be possible to shape the building skin to shade the windows so that a less efficient and less expensive glazing is needed. In addition, exterior choices should be weighed in the light of their impact on the environmental soundness of the interior.

“Use your structure so that you don’t have to add more material just to get a nice finish on the inside walls,” says LHB’s Schoessler Lynn.

Resources for green envelope design Fortunately for facility executives, tools are available to help sort through the many layers of decisions involved with designing a green envelope. Energy modeling and life-cycle costing can give facility executives a solid idea of the costs and benefits associated with their choices before a facility is built. And the U.S. Green Building Council’s LEEDTM (Leadership in Energy and Environmental Design) Green Building Rating System provides facility executives and designers with a framework for assessing the performance and environmental characteristics of facilities.

“LEED is all about integrating the design process,” says Brendan Owens, lead engineer with the U.S. Green Building Council. “It takes all the traditional disciplines, such as mechanical, architectural, etc., and brings them together at the very beginning of the project to establish goals.”

Unfortunately, though, some of the tools that would assist in the specifying of products and materials for green envelopes do not yet exist. As a result, the process of weighing all the countless pros and cons and trade-offs involved with green design can be a difficult one.

Tools to help evaluate energy performance have been around for quite a while, but that’s not the case when it comes to understanding the overall environmental impact of products and materials, says Foss. “The answers on the materials side are not got at very easily.”

Not Easy Being Green

It’s not difficult to understand why environmental responsibility makes sense where energy efficiency and IEQ are concerned. Green performance in both areas translates to the bottom line in energy cost savings and productivity gains. And green materials do not always cost more.

“We’re seeing more and more metal siding with a higher percentage of recycled content,” says Gibney. “That sort of thing does not necessarily cost more.”

Once you get beyond basic good, energy-efficient design, though, the benefits of green-mindedness aren’t always as clear.

“We are still struggling with ways to get payback on some of these strategies,” says HOK’s Nelson.

And while the benefits of environmental commitment sometimes come in forms other than bottom-line savings, such as easier access to permits in some locations, it takes a real organizational commitment to build an envelope that is truly green in the fullest sense of the term. In addition, it takes an ingrained understanding and full buy-in on goals and priorities. For example, are concerns primarily with energy efficiency, or with the whole life-cycle impact of the facility and issues like pollution and embodied energy?

The right architect and engineer should be critical partners in helping to sort out the answers to these questions and determine how best to achieve goals, but it’s crucial, experts say, not to abdicate too much responsibility.

“The green projects that really work well have all been ones where the owner’s commitment drove the whole process,” says Reed. “The message to the architect was, ‘We’re doing this. Now how can you make it happen?’

“It’s the difference between a drive to do the right thing and a desire to get the right stuff.”

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  posted on 9/1/2003   Article Use Policy

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