Energy-efficient Building Envelopes: Reducing Heat Loss And Costs

Energy-efficient Building Envelopes: Reducing Heat Loss And Costs – In 2017, Hurricane Maria hit Puerto Rico, destroying the island’s infrastructure and killing 2,975 people. In the subsequent investigation, officials found that while the code-built buildings remained largely standing, water had still entered them and severely damaged the buildings’ interiors.

The disaster sheds light on one of the most important parts of the building’s resilience – the building’s climate screen. Built to keep the outside out, the envelope ensures our buildings are comfortable and safe. But the codes behind the envelopes are written for a world without climate change, and extreme weather makes them obsolete.

Energy-efficient Building Envelopes: Reducing Heat Loss And Costs

Energy-efficient Building Envelopes: Reducing Heat Loss And Costs

What happens when old building envelopes meet new weather events? And what do people in the architecture, engineering and construction (AEC) industry do about it?

What Direction Should A House Face To Maximize Its Energy Efficiency?

The building envelope is the physical barrier between the inside and outside of a building, including elements such as windows, walls, roofs and foundations. The envelope is responsible for four main functions: structural support for the building and control of moisture, temperature and air flow.

When the U.S. The National Institute of Standards and Technology (NIST) visited Puerto Rico months after Hurricane Maria, found that code-built buildings were generally still standing, but that water damage to the buildings’ interiors had rendered the structures unusable‚ÄĒa failure in moisture management.

According to NIST’s preliminary report, code-built buildings such as hospitals and schools had “good structural performance” but “suffered extensive nonstructural damage and loss of function.” Unfortunately, roofs, doors and windows were the weak points and the rain could penetrate undamaged doors. “If a critical building loses its ability to function due to rainwater intrusion, you are unable to provide services,” said Erica Kuligowski, the leader of the NIST team.

Hurricane Maria is a worst-case scenario. But what other challenges does global climate change pose to our building scales?

High Performance Building 101

There is a reason why climate change was originally called “global warming”: one of the most obvious symptoms is that the Earth is warming at an unprecedented rate. Heat is already the leading source of weather-related deaths in the United States, and vulnerable populations such as young children and the elderly bear the brunt of hot weather. Building envelopes are designed to regulate their buildings to a comfortable temperature, but the hotter it gets, the harder it will be to keep people inside cool.

A partial solution is to use techniques from the Passivhaus standard, a voluntary energy efficiency standard that reduces the need for electric heating and cooling. These houses are well insulated and have a “tight” building frame to provide more control over air flow and temperature.

A Passivhaus standard is heat recovery ventilation systems, which respond to cold weather by “recovering” heat from outgoing air and using it to heat incoming fresh air. In warm weather, the system works in reverse, “recovering” heat from incoming warm air to warm outgoing cold air.

Energy-efficient Building Envelopes: Reducing Heat Loss And Costs

Passivhaus-trained architects also use solar shading, a fancy-sounding phrase that essentially means limiting the amount of sunlight that falls directly on the building’s climate screen, through interventions like strategically planted trees and outdoor shutters or blinds. Finally, another Passivhaus standard is cross ventilation, which uses the old-fashioned cross breeze to cool houses.

The Role Of Building Envelope In Achieving High Performance Goals

Water poses a serious threat to buildings during tropical storms, but wind can be just as dangerous. During a hurricane, both lateral (horizontal) and uplift forces can be dangerous to a building’s structural integrity. Building openings such as doors and windows are vulnerable to breaking in during high winds, and the rushing wind can build up enough pressure on the roof to tear it off. Updrafts can also lift the roof, making the structure more likely to collapse.

There are a few envelope adjustments that can make this kind of collapse less likely. First of all, small adaptations such as automotive-style impact glass and hurricane shutters will make the openings less likely to let in the wind. Secondly, buildings with a continuous load path are less vulnerable to wind. In practice, this means anchoring the roof to the foundation.

Nicknamed the “Eye of the Storm”, this monolithic concrete house is resistant to high winds. (Image courtesy of Pareto Group.)

At the more extreme end of wind adaptation, domed buildings have few surfaces that can be affected by lateral or uplift forces, giving them a low drag coefficient. This is especially true for monolithic dome buildings; dome-shaped buildings are cast in one piece, without separate roof and walls. The “Eye of the Storm” home, built in South Carolina, is one of the most famous examples of monolithic dome construction. Built after its owners lost a home to Hurricane Hugo, the building is made entirely of steel and concrete.

The Biggest Sources Of Energy Loss In Old Homes

As the climate changes, buildings may have to contend with more flooding, both from rising seas and extreme rainfall. And flooding is expensive for buildings. This year’s spring floods in Nebraska and Iowa cost $3 billion alone.

At the individual building level, there are three specific types of flood management strategies: avoidance, water exclusion, and water intrusion. Avoidance includes strategies that focus on ensuring that flood waters do not even reach the envelope, either by elevating the building or by outright prohibiting buildings in flood-prone areas. But exclusion and entry strategies both circle the envelope.

Water exclusion strategies designed to keep water out of a building include low-tech solutions such as sandbags and plastic strips around the building. Water penetration strategies, also known as “wet proofing”, are strategies designed to limit the damage to a building once it has been breached.

Energy-efficient Building Envelopes: Reducing Heat Loss And Costs

Water intrusion strategies are extremely effective because they prevent the build-up of hydrostatic pressure that can cause serious structural damage, but they are less commonly used. An example is flood valves, small vents designed to let water into an area like a crawl space or a garage when floodwaters top them.

Innovative Approaches To Building Envelope Design For Energy Efficiency

Often, buildings use a bit of each strategy to more effectively manage flooding. An example of a multi-strategy building is Clippership Wharf, a mixed-use residential development on the Boston waterfront. The building’s architects insert a “living shoreline,” a 10-foot intertidal zone with terraces designed to drain and fill with the tide, to set the buildings back from the shore (avoidance). But they also flood-proofed the building envelope itself and planned for a 100-year flood (a flood with a 1 percent chance of occurring in a given year).

The architects used removable flood planks, aluminum planks stacked on top of each other to create a waterproof barrier that can slide into place to protect entry points before a flood, as an exclusion strategy. They also planned exit doors above the 100-year water line with stairs down to reduce the likelihood of people being trapped in the building or letting water in. Finally, as a strategy for water ingress, they planned for the lowest floors to be broken, and put the electrical and plumbing work into the ground floor instead.

Photo 2. Removable flood planks like those used to protect Boston’s Clippership Wharf. Courtesy of PS Flood Solutions

The waterproofing strategies made the building slightly more expensive, but were well received by the local community. “These are real questions that are important today,” said Steven Caswell, one of the architects behind the project, at this year’s American Institute of Architects (AIA) conference.

How To Calculate Form Heat Loss Factor.

As the weather becomes more extreme, some governments are beginning to revise building standards. The National Research Council of Canada will address adaptations to climate change during the 2015 to 2020 code cycle,  potentially including basement flood prevention standards and more concrete flood adaptation.

But there’s a problem: often the people most vulnerable to extreme weather are the least likely to have the money for smart building upgrades.

While Hurricane Maria saw the envelopes of code-certified buildings fail, it also saw the far more catastrophic failure of buildings that had not been certified at all. In total, 55 percent of the island’s housing was built without proper code compliance (https://www.builderonline.com/building/building-science/hurricane-maria-shows-that-code-built-housing-holds-up-better_o), and many of these informally constructed houses collapsed or were severely damaged when the hurricane hit.

Energy-efficient Building Envelopes: Reducing Heat Loss And Costs

Last year, the Fourth National Climate Assessment found that climate change in the United States will hit low-income communities the hardest. Low-income communities are more likely to have buildings without adequate insulation or air conditioning and are less likely to have the resources to repair those buildings after a disaster. “Some property owners can afford to modify their homes to withstand current and projected flooding and erosion impacts,” the report reads. “Others who cannot afford to do so will be financially tied to homes that are in greater risk of annual flooding.”

Aligning Historic Preservation And Energy Efficiency

Developments like Clippership Wharf are certainly a step forward, but these green innovations are still too expensive for many Americans. Today’s architects and designers are definitely pushing the envelope when it comes to climate-ready building design. The question is, are they pushing it far enough or fast enough to the people who need it most?

U.S. Midwest flood costs estimated at more than $3 billion. CBC News. 2019, March 22. Available online at https://www.cbc.ca/news/world/midwest-floods-economic-cost-1.5068037

Flood resistant construction and adaptation of buildings. Oxford Research Encyclopedia, Natural Hazard Science. 2017, Dec. Access online at https://oxfordre.com/naturalhazardscience/view/10.1093/acrefore/9780199389407.001.0001/acrefore-9780199389407-e-111?larskeyresz=111?rskeyresz=1

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