The thermal envelope of a building has a big job. According to the National Renewable Energy Laboratory, the thermal envelope is “everything that serves to shield the living space from the outdoors. It includes the wall and roof assemblies, insulation, air/ vapor retarders, windows, and weather stripping and caulking.” The outdoors includes everything from heat and cold to moisture to insects. The results of an efficient thermal envelope include improved indoor air quality and energy efficient living.
To achieve a comfortable living space, it is necessary to ensure that the thermal envelope is designed and built properly. While it is possible to improve the thermal envelope in an existing building with new insulation, windows and doors, an older building will never achieve the level of efficiency in a well-built new home.
Attacked by so many outside elements, a structure must be built with an efficient thermal envelope. This envelope, however, must not put an undo financial burden on the building owner. The efficiency savings recognized with a well-built thermal envelope must not be negated by the cost of building.
Sponsored by Hi-Tech Building systems, a distributor for ThermaSteel RP™ structural steel insulated panels (SSIPs), this report will explore the benefits of a thermal envelope built with SSIPs.
SLOW THE FLOW
Heat always moves from hot areas to cold areas. During summer, heat from the outside will flow toward the cooler inside. In winter, the opposite is true. The job of good insulation is to slow this flow.
A good thermal envelope will enable heat and cold to stay indoors while keeping the elements out. The last thing wanted is to lose the money spent on heating and cooling through poorly insulated walls. The best way to evaluate insulation is using the R-value. Different areas have varying requirements for insulation in attics and walls. According to EnergyStar for Homes, attics in an average climate usually should be around R-30 while walls should be at least R-13 to R-15. These numbers will adjust based upon the average temperature in the area where a house is built. Generally speaking, however, the higher the R-value, the more energy efficient a home will be.
R-value cannot be blindly viewed. Actual insulation efficiency or effective R-value is drastically affected by thermal bridging. A thermal bridge is an area where a poorly insulated material allows for easy passage of heat flow across a thermal barrier. One of the most common examples are wood wall studs. Wood inherently has an R-value of only 1 or 2. This lower value offsets the efficiency of, say, fiberglass bat insulation proportionally. So, if a wall is filled with an R-19 insulation and wood studs are placed 16 inch on center, nearly 25% of the wall is solid wood. As such, only about 75% of the wall actually has an efficiency of R-19, resulting in an effective R-value of about R-14.
To truly achieve peak efficiency, it is necessary to avoid thermal bridging as much as possible. ThermaSteel SSIPs, consisting of structural grade steel and Expanded Polystyrene (EPS), boast of no thermal bridging as a result of the offset steel studs. As such, a wall or built with structural steel insulated panels will have a consistent R-value throughout, providing an effective R-value of R-19 – about 136% over that of a traditional wood or steel frame building with 6 inch walls and R-19 bat insulation.
SHED THE WATER
The thermal envelope is bombarded by rain and wind. Effective vapor barrier is essential, but humidity and rain can still permeate the envelope. During a rainstorm, the pressure difference between inside and outside can actually suck water into small leaks around windows and doors and though breaks in the vapor barrier. This, along with moisture created inside the building, can infiltrate walls and lead to mold and mildew.
Modern, high efficiency construction is much more air tight than older buildings so they are able to maintain comfortable levels of temperature and humidity. This ability increases the psychometric stresses driving moisture into the building envelope. Many high-performance building materials include paper and resins that are subject to attack by mold and bacteria. Even wood is conducive to such infiltrations. Such microorganisms lead to poor indoor air quality, illness, and allergies. Contrarily, the steel and EPS that makes up a structural steel insulated panel are impervious to mold and mildew.
An efficient structure is tight. An air tight envelope can create problems with air quality, however. Fresh air not flowing as freely from the outside not only translates into better thermal efficiency but also holds allergens and “bad air” captive.
Most energy efficient homes have natural air infiltration rates of 0.2 to 0.5 air changes per hour (ACH). While this is technically enough to meet current indoor air quality (IAQ) guidelines, natural air leakage in and out of a building varies with outdoor conditions. Thus, these structures do not ventilate reliably and some areas may be left unvented.
Poor IAQ can result from a variety of sources ranging from smoking to elevated levels of Radon gas. Building materials can present high levels of volatile organic compounds (VOCs) including formaldehyde. Likewise, as discussed previously, leaks and high indoor humidity can lead to mildew and mold, releasing airborne spores.
According to a report written by Dr. Awbi, who is professor of the built environment at Reading University’s school of construction management and engineering, “Poor indoor air quality is connected with a range of undesirable health effects, such as allergic and asthma symptoms, lung cancer, chronic obstructive pulmonary disease, airborne respiratory infections and cardiovascular disease.”
While electronic air cleaners and increased ventilation can help with IAQ to an extent, it is best to start at the beginning and ensure that building materials lend themselves to reduced pollutants. Wood and fiberglass insulation emit VOCs including formaldehyde. These emissions are consistent with poor IAQ. EPS and steel are intrinsically VOC free, with no off gassing, making ThermaSteel panels an effective method of building a thermal envelope.
While bugs might be an acceptable nuisance on a camping trip, it’s safe to say that they are not normally welcome inside a building. Whether termites that eat their way in or insects that come in through cracks in the walls and roof, bugs can be a health hazard. Infestations can lead to allergy and asthmatic attacks. Bites and stings are irritating and can be toxic.
While it may not be possible to fully eradicate bugs from a building because of open windows and doors, it is feasible to reduce their accessibility. ThermaSteel panels are mounted tightly with shiplap joints making it harder for bugs to get in. In addition, the materials used in ThermaSteel SSIPs are naturally impervious to insects, making them a poor meal choice for termites and other boring insects.
SAVE THE PLANET
Sustainable building materials help lighten the footprint of any construction project. They reduce the impact on the environment by using products that are either completely renewable or gathered in a way that doesn’t mar the surrounding area, pollute the air, or permanently reduce the supply. They provide further benefits during the building’s lifecycle by reducing waste and increasing energy efficiency.
An efficient thermal envelope is, by nature sustainable because of its ability to reduce the energy needed to heat and cool a structure. The materials used, however, can be sustainable or not.
According to the Argonne National Laboratory, it would take one hundred 8.5in diameter trees to build a 1500 sf home. That is nearly an acre of forest. Conversely, a home of the same size built with ThermaSteel would only use the amount of steel from two recycled cars. The panels use 80% recycled steel in the manufacturing process.
At the same time, the panels’ steel and EPS can be recycled. In regards to EPS, this material is made of recycled materials and contains no VOCs. Recycled EPS is actually used in the manufacturing of other building materials, furniture, and toys.
Since ThermaSteel panels are free of any VOCs, they do not off-gas. As such, they do not add to greenhouse gasses or damage the ozone layer.
One way that building projects impact the environment is through the waste created. This garbage fills landfills and takes an inordinate amount of time to break down. The more that is in the landfill, the more environmental impact there is in the form of off-gassing and other forms of terrestrial toxins. ThermaSteel panels are made to order for a building project. As such, there is scarcely any waste on the jobsite. This is in contrast to approximately 20-40% waste factor for lumber on traditional job sites.
SAVE THE DOUGH
Ultimately, none of the aforementioned benefits make a difference if a building costs too much to build or own. ThermSteel SSIPs are far more economical as a building method than many other high-performance building supplies including insulated concrete forms (ICFs) and hollow blocks. In comparison to traditional wood building, ThermaSteel panels add only 3-5% to the overall budget. In the bigger picture, however, there are areas that will ultimately offset this increase.
Because of the ease of erection, a building built with ThermaSteel can be done far faster than other building options. As such, the cost of labor is less. To that end, it bears mentioning that one reason that building with ThermaSteel is faster is that the panels combine the jobs of structural framing, insulation, sheathing, and a vapor barrier in one fast, high-tech step. This cuts labor by 75% since the panels just need to be put up and not visited repeatedly to accomplish all the key elements of building a thermal envelope. The 4’ x 8’ panels are light and manageable. A single person can lift and move the panels, making it easy for a crew to work efficiently.
As mentioned previously, there is little waste when building with ThermaSteel panels. The leftover material can easily fit in the bed of a pickup truck avoiding the need for expensive dumpsters and waste removal.
These savings are only the tip of the iceberg. Saving during the construction period is one thing, but the real savings comes in the many years of ownership. Because of the level of energy efficiency, the owner of a building built with ThermaSteel panels will spend 50-70% less on heating and cooling when compared to a conventionally constructed building. Case in point, one 138,000 sf all electric senior housing complex spends less than 3 cents per square foot on electricity each month.
About the Sponsor
Hi-Tech Building Systems is a licensed distributor of ThermaSteel structural steel insulated panels. Located in the Chicago area, the company works with homeowners, project managers, architects, and builders throughout North America, South America, and the Caribbean. Projects range from single family homes to industrial buildings to commercial projects.