Learning Objectives - After reading this article, you should be able to:
- Evaluate at least three negative impacts of buildings on the environment.
- Identify the six elements of the building envelope discussed in this article.
- Specify at least one sustainability benefit for each of the six elements that advances in chemistry have made possible.
- Explain how at least one of the sustainability advances discussed in the article has helped create a higher-performing building envelope.
|1 AIA LU|
|1 GBCI CE Hour|
Today’s architect knows that successful and repeatable sustainable design is a complex undertaking dependant on the collaboration of best-in-class design-build teams. What many architects may not realize, however, is that extending the traditional definition of this team to include building product manufacturers may provide new opportunities to access world-class research and development in the area of sustainable construction practices.
Specifically, chemists are continuously discovering ways to improve building products and, at the same time, providing the industry with much-needed metrics for defining sustainability including third-party verified analysis of environmental impacts and life-cycle assessments. The result is that today’s construction professionals can now access a vast portfolio of sustainable building solutions that were unimaginable just 10 or 20 years ago.
The following article will address the sustainability benefits of building envelope elements that have been advanced by chemistry.
Design professionals play a major role in slowing, stopping and perhaps someday reversing, the negative impact buildings have on the health of the planet. The factoids and statistics are plentiful.
Commercial buildings alone use 20 percent of our energy and cause 17 percent of the annual greenhouse gas (GHG) emissions in North America, according to ENERGY STAR data. Residences use another 20 percent of our energy and emit a similar amount of GHGs — namely 1,270 megatons. Let’s see: 1,270 million tons or 1,270,000,000 tons or 2,540,000,000,000 pounds — that’s 2.54 quadrillion pounds of harmful gases. Combining residences and commercial buildings, that’s more than 5 quadrillion (16 zeros!) pounds of foul air every year. Let’s get to work!
According to www.epa.gov/greenbuilding, buildings accounted for 72 percent of total U.S. electricity consumption in 2006, and this number will rise to 75 percent by 2025. Building occupants also use 13 percent of the total water consumed in the United States per day. In addition, building-related construction and demolition debris totals approximately 160 million tons per year, accounting for nearly 26 percent of total non-industrial waste generation in the U.S.
However, on the bright side, a properly designed, high-performance building envelope can reduce a structure’s energy consumption by as much as 40 percent, according to Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use, National Institute of Standards and Technology. And as architects, we know a 40 percent savings is very possible: some of us are doing that and better every day.
Even these few but dramatic facts make it clear that improved performance of the building envelope is critical to reducing our collective carbon footprint and making our built environment more sustainable — albeit one building at a time. Each building (envelope) we create is a functional system of construction components, which — at a minimum — must protect its inhabitants against sun, rain, snow, hail, wind, dust, pollutants, allergens and pests, all while provide structural integrity as well. In addition, sustainability remains an overarching imperative that a high-performance building must also address through the components of its building envelope.
Design-build teams are faced with countless decisions and held responsible for the long-term consequences. Many of those decisions benefit from discoveries in chemistry, which are then adopted and adapted by building product manufacturers, who then create and supply increasingly sustainable products or assemblies. This article looks at the performance benefits that advancements in chemistry bring to each of six building envelope components:
- Wall Systems
- Air and Weather Barriers
1. High-Performance Foam Insulation Materials
All can agree that a high-performance, sustainable building is dependant on a high-performance building envelope. Optimizing exterior and interior walls, roofs and foundations with plastic foam insulation provides many benefits for reducing energy demand, improving indoor air quality, reducing moisture and pollution infiltration and extending the service life of the building as a whole. We will look at three plastic foam insulating materials in the section below, including:
- Spray-applied polyurethane foam (SPF) insulation, air barrier and roofing systems (closed and open cell)
- Extruded polyurethane (PU)
- Expandable polystyrene (EPS)
Spray-Applied Polyurethane Foam (SPF)
SPF is used in a number of ways in construction. SPF is a two-component product that is manufactured onsite, but engineered in the molecular level to optimize performance for a specific application. By varying key components, the finished product can be modified to meet specific performance requirements for roofing applications, insulating air barrier systems, adhesive applications or wall insulation.
SPF insulation has two basic formulations: open-cell (low-density (LD) 8 kg/m3 to 12 kg/m3 (0.5 to 0.7 pcf) and closed-cell (medium-density (MD) 24 kg/m3 to 48 kg/m3 (1.5 pcf to 3 pcf). (A third formulation, high-density (HD), is used for roofing applications.) For each cell type, the liquid — comprised of isocyanate and a formulated resin — is mixed in the spray gun and then propelled by a blowing agent — water for open-cell and a chemical blowing agent for closed cell. In both cases, the formulations have no ozone-depleting blowing agents, formaldehyde or any ozone depleting chemicals, and they emit low to no VOCs. The formulated resin portion of any SPF product uses a very small amount of a renewable resource like soy oil or sucrose-based oil, but in all cases that natural component is negligible. The catalyst starts when the pressurized mix comes out as a liquid, rises as a foam and can expand up to 30 times. The major differences are:
- Open-Cell SPF is soft to the touch, has an R-value around 3.5 per inch, and is usually less expensive than closed-cell foam. It is water blown in place. An open-cell foam is defined as having around 60 percent of the cells within the material open (think popped bubbles), making it useful to absorb sound, but should not be used as a vapor or water barrier.
- Closed-Cell SPF is defined as having greater than 90 percent of the cells within the material closed and is chemically blown (with zero–ozone-depleting blowing agents), expands rapidly and significantly upon application, fills all voids, and sets up hard, forming a rigid foam plastic. It chemically bonds to the surface to which it is sprayed. It is an excellent air, moisture and vapor barrier, but not a sound absorber. It is denser, heavier, and offers the superior insulating performance of the two with an R-value around 6.5 per inch of thickness. It is usually more expensive.
In addition, SPF (and any closed-cell plastic foam insulation material) is FEMA-approved for flood prone areas. Because it is rigid and monolithic, its increased strength makes it an appropriate material in hurricane zones. The National Home Builders Association’s SPF research determined that it provides significant racking resistance in stick built projects, providing some structural benefit as well.
SPF is an efficient insulation material for roof and wall insulation (as we will discuss shortly), insulated windows and doors, and air barrier continuity components (sealants) — all contributors to reduced air leakage (infiltration or exfiltration), which accounts for 25 percent to 40 percent of (wasted) energy use according to ENERGY STAR studies.
As a high-performance insulation material, SPF can reduce the amount of fossil fuels needed to heat and cool buildings, reducing the resulting greenhouse gas emissions, and may require less energy to produce than some other insulation products. Plus, the amount of energy required to transport and install SPF is also minimized in comparison to other alternatives, according to a life-cycle Eco-Efficiency Analysis.
Finally, SPF is durable and maintains its physical properties over time. In a vertical wall application, it should last the lifetime of the building. In a low-slope roofing application, its lifespan can be renewed indefinitely with simple recoats (read more about SPF roofing below). It contributes little to the waste stream, and in a single product (depending on the formula and application, as well as local code requirements) can do the job of three or four products — insulation, air barrier, sealant, vapor barrier and weather barrier. Spray-applied polyurethane foam insulates and eliminates thermal bridging through fasteners or gaps in decking.
Extruded Rigid Polyurethane (PU)
Polyurethane PU foam has an R-value of 6.7 per inch of material and is a closed-cell foam that uses a zero-ozone-depleting chemical blowing agent. It exhibits most the performance characteristics and benefits of closed cell SPF, but is engineered to be poured-in-place rather than spray applied. Rigid closed cell PU can be found in a variety of densities and is a key component used in Structural Insulated Panels (SIPs) for walls, floors, and roofs, as well as Insulating Concrete Forms (ICFs), insulated masonry block, entry doors, garage doors, exterior shutters, insulated siding and many insulation applications in civil engineering and infrastructure projects. PU is a key ingredient in OEM products such as weather stripping, gasketing and door sweeps. Outside of insulation, PU can be found in interior and exterior moldings and trim, ceiling medallions, decking, railings and porch posts, architectural columns, louver gable vents and composite board stock.
Expandable Polystyrene (EPS)
EPS offers an R-value of 3.5 per inch and is traditionally used for board stock insulation, and in wall systems such as SIPs, ICFs and Exterior Insulated Finishing Systems (EIFS). Patented in 1950, EPS is a cost-effective and easy-to-handle insulation material. As a closed-cell plastic foam insulation material, it is FEMA approved for use in flood zones.
A recent development in EPS is the advent of graphite-enhanced formulations. Graphite-enhanced EPS features microscopic flakes of graphite that work as small mirrors to reflect heat back into the environment and increase insulation value up to 20 percent versus standard EPS, reducing the thickness of insulation needed for equal results. In retrofit applications, the insulation is attached to gypsum board and installed on the interior side of exterior walls to provide a one-step process for both interior finishing and enhanced insulation performance. For new construction, graphite-enhanced EPS is gaining popularity for SIPs, ICFs and EIFS.
Energy efficiency is the major environmental and financial benefit these high-performance insulation solutions provide. Insulating R-values and resulting performance can be twice as effective as traditional materials.
- Stop thermal bridging, which occurs when materials that are poor insulators come in contact with each other, allowing heat to flow through the path created. Insulation around or beside a bridge is of little help in preventing heat loss or gain due to thermal bridging. The bridging can be improved or eliminated by creative design to “dismantle the bridge” or by using materials with better insulating properties in the bridging configuration itself or by using more effective insulation products to block or isolate the heat/cold from reaching the bridge.
- Reduce or eliminate convective loops, which are wall and ceiling cavities that act as room-sized heat exchangers, relentlessly pumping heat out of a space (to an attic or basement) even if there is no direct air leakage from indoors to outdoors. Convective loop heat losses occur in buildings within and at the top or bottom of uninsulated, wood-framed or metal stud interior partition walls and, of course, in hollow core masonry walls. They can be eliminated as well with proper application of SPF insulation that seals the cracks and crevices and inefficient wall assemblies that facilitate convective loops.
- Likewise, uncontrolled air leakage can be reduced or eliminated with proper specification and application of high-performance insulation products like those discussed here.