SPECIAL FEATURE 10 Thi n g s t o Kno w A b out Net Zer o
Net zero buildings are highly effi cient structures that produce as much energy as they use. The zero-energy design principle is growing in importance due to increasing costs of traditional fossil fuels and their negative impact on the planet's climate and ecological balance. It’s entirely possible to construct a building
that produces enough of its own power that it does not consume energy from the grid. An energy- plus building can even produce more power than it consumes, converting it into a mini power plant. The following 10 things will tell you more about migrating to net zero buildings.
1. Why bother with buildings? Commercial and residential buildings consume about one-third of the world’s energy. In the United States, buildings account for more than 40 percent of total energy consumption, including 72 percent of electricity generation, 12 percent of water consump- tion and 60 percent of all non-industrial waste. According to a report by the National Science and Technology Council Subcommittee on Buildings Technology, Research and Development, if current trends continue, by 2025 buildings worldwide will be the largest consumer of global energy, more than the transportation and industry sectors combined.
2. Push the envelope. Metal building systems have higher air leakage compared to other types of construction. Without
focusing on their underlying metal building enve- lope design and incorporating high R-value continu- ous insulation to produce an air-sealed solution, achieving net zero success will be very diffi cult or ineffi cient. New ASHRAE 90.1 energy codes require building designs to comply with air infi ltra- tion requirements. Individual materials must have a maximum air permeance level no greater than 0.004 cfm/ft2. Additionally, building systems or assemblies must have a maximum air permeance level no greater than 0.04 cfm/ft2. By adding a continuous blanket of insulation,
and sealing additional junctures and penetrations in the building envelope with foam sealants, a sig- nifi cant reduction in heat loss can be economically realized. This heat loss would otherwise have to be accommodated by additional energy-generating technologies, such as solar panels. “In a metal building, thermal shorts reduce the
R-value of cavity-insulated wall systems by more than 50 percent,” says Doug Todd, market manager of commercial construction at Dow Building Solutions, Midland, Mich. “Installing a layer of high R-value con- tinuous insulation over the steel studs reduces the impact of the highly conductive steel. For example, 1/2-inch-thick board R-3.0 THERMAX insulation has the same thermal resistance equivalency to 10 feet of steel, close to 250 times more effective.” But insulation is not enough, especially in a net
zero building. If the building envelope leaks air, the overall impact of the insulation is compromised.
“Dow has identifi ed cost-effective, fi eld-tested methods to detail the insulation as an air barrier using tapes, PVC joint clips, insulation edge treat- ments, construction grade sealants and adhesives, and air sealing foams such as FROTH-PAK Foam Insulation and GREAT STUFF PRO Insulating Foam Sealant,” Todd says.
3. Insulated panels are a plus. Walls have been insulated for centuries, ever since animal skins were fi rst hung on rock walls or sod huts were crafted with thick dirt walls. Today, insulated metal panels (IMPs) aid net zero efforts by producing an airtight, moisture-resistant, rigid, continuous-insulation solution. IMP’s high R-values provide superior thermal performance and reduced energy consumption. This allows for smaller green- house gas emissions and reduced energy costs for building owners, which contribute to net zero suc- cess. IMPs mitigate thermal drift, a degradation of R-values over time. Thermal drift is common when using un-faced polyisocyanurate rigid board insula- tion, which can lose up to 20 percent of its R-value within two years. IMPs can be integrated with other building
envelope solutions, such as windows, louvers and sunshades, to further push toward net zero. IMPs can be coated with cool roof colors, which offer potential energy savings throughout a roof’s lifetime. This helps mitigate the urban heat island effect in urban areas.
This Net Zero Energy School Building prototype designed with Butler Manufacturing metal building systems won the prestigious 2011 Silver in the North America Region Holcim Awards. (Image courtesy of Butler Manufacturing)