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High-Performance Building Envelopes

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Tight building envelopes provide occupant comfort and a healthy environment

high performance building envelopes,The building envelope is made up of many different components: roof, walls, windows, doors, etc. The building envelope acts as a thermal barrier, playing an important role in regulating interior temperatures and determining the amount of energy required for optimal thermal comfort. Creating a high-performance building envelope means each piece is designed to minimize the transfer of thermal energy, which in turn creates an energy-efficient or tight building.

The design of the building envelope can determine the amount of lighting, heating or cooling it will need. For James Pastine, project manager and project designer at Crawford Architects, Kansas City, Mo., the essential elements of a high-performance building envelope are the combination of the building skin and the openings in it. The key is "Getting those two elements to function together to provide the best environment possible for the end user of the building," he says.

In addition to good windows and fenestration design, Brian Court, AIA, partner, and Jim Hanford, AIA, LEED AP BD+C, principal, at Miller Hull Partnership, Seattle, say balancing heat loss, solar control, daylighting and glare is essential. Next is airtightness, since undesired infiltration affects long-term durability through moisture control, HVAC sizing, energy efficiency and occupant comfort.

A high-performance building envelope should employ sustainable strategies to provide a healthy and comfortable environment for the building occupant, adds Ruth Ro, AIA, LEED AP BD+C, associate principal at New York City-based Dattner Architects. "This means, starting in the schematic phase, you consider passive strategies that would affect performance--building orientation, solar exposure, climate. Then, in design development, you consider material selection, solar shading and daylighting strategies."

 

Climate and Location

Where a building is located plays a role in how the building envelope is designed. In colder climates, the building envelope reduces the amount of energy needed to heat the building, while in hotter climates, it can reduce the amount of energy needed for cooling.

While understanding the climate is a good starting point, Pastine says it's important to know how much a building is going to have to be insulated, and what kind of environment it's going to be in. "Is it going to be hot and dry? Is it going to be cold and wet? Is it going to be wintery? Is there going to be huge rains?" he asks. "Once that is determined specifically, we have to respond to the very local environment on the site, such as the building's orientation, adjacent buildings near it, the temperature it's going to function in, etc."

The climate determines the strategy in designing the building envelope. "In a mixed climate, we depend on mechanical systems to provide a comfortable indoor environment most days of the year," Ro explains. "The goal is to reduce the heating and cooling loads."

While energy efficiency is the primary goal, Court and Hanford say occupant comfort is just as important. "Access to natural light and ventilation while controlling for glare are high priorities," they add. And, they note, working with the mechanical and electrical systems to integrate the envelope's performance with system selection and sizing is also important.

"Solar heat gain and glare control on the east and west façades can be challenging," explain Court and Hanford. "Often, the best solutions-such as limiting fenestration on these façades- isn't always an option. The next best solution is often the most expensive-automated exterior blinds, for instance."

 

Insulation Performance

When it comes to choosing the proper insulation for a high-performance building envelope, Pastine says he is looking for something that is going to perform well over time and won't break down. "It has to have a continuity throughout the entire envelope of the building," he says. "You don't want any cold or hot spots. And getting our air barriers and vapor barriers in the correct location, depending on the climate that we're in."

"Continuous insulation with no interruptions is important in reducing heating and cooling loads," Ro explains. "Not only is this good practice, but it is required by code. Insulation with a tested R-value is meaningless if it is interrupted by metal study every 2 feet." And, she adds, it is important to be mindful of all instances of thermal bridging. "That metal stud or metal girt will act as a thermal bridge same as a non-thermally broken aluminum mullion." 

Ro recommends looking for a higher R-value per inch of material. For instance, closed cell foam insulation has an R-value of 6.5 per inch and also acts as an air and moisture barrier. "This type of insulation has to be tested as part of an assembly to conform to non-combustible construction requirements," she says. "This is typically achieved with a thermal barrier like a layer of gypsum board, metal panel or even a spray-applied coating."

 

The Right Solution

Research and working together is essential when designing a high-performance building envelope. "Buildings and building envelopes have become a significant team effort," Pastine explains. "We meet with experts on all the different particular products, we meet with engineers and consultants, as well as contractors familiar with new construction methods, and we evaluate other facilities. We compare products and systems for performance, cost and longevity, and then take all of that research and build a big knowledge base to choose the right solution for a building. It helps from a design standpoint, it helps from a cost standpoint, and it gives us all of the information that we need to be armed with to recommend the right solution to our client."

And, Pastine says one of the biggest challenges is educating clients about the right solution. "We have to be full of knowledge ourselves as designers to be able to come to them with an appropriate solution, especially if it is something that they have not gotten before. A lot of clients, contractors and architects are resistant to doing anything different than what's been done for the last 20 or 30 years."

To do that, he recommends keeping up with the latest technology, arming yourself with the right information to be able to prove that this new way of doing things is the right way of doing things. "Sometimes they get it, and sometimes they don't," Pastine explains. "Sometimes they see that it's going to be a bit higher cost upfront, and so they just want to go back to what they've done before. They can do it that way, but they're not realizing the full life cycle costs of the building or that they'll be able to recoup a lot of their costs by having systems inside the building that can function very efficiently and minimally. Just because we've designed the exterior better."

Simplicity is key, Ro says, when designing for energy efficiency. "Whenever a window is placed in a deep recess or whenever the material changes, keep in mind that these sections need to be detailed thoroughly and with constructability in mind," she says. "Fortunately, there are so many products that allow for deviation while maintaining a high performing building envelope."

 

*Image credit: HUB in Downtown Brooklyn, designed by Dattner Architects and developed by Steiner NYC