Before you start comparing numbers, you need to determine the true energy efficiency of your building envelope. A building’s energy efficiency is more than just an insulation’s tested R-value. The whole-wall R-value is a more accurate measurement of real-world performance compared to the insulation’s R-value alone. Many studies show a building’s airtightness has more of an impact on energy efficiency than these popular terms. Premier SIPs help reduce energy consumption, lower construction waste, support healthier indoor air quality and create a more comfortable living and working environment. The clear advantage of building with Premier SIPs is a stronger, advanced construction product with fewer impacts on the environment.
Airtightness in SIPs vs Stick Framed Construction
In a study by the Department of Energy’s Oak Ridge National Laboratory, two identical test rooms were built side by side. One stick-framed, one SIP-framed. Rooms were tested for air infiltration and the SIP room was FIFTEEN times more airtight, and more energy efficient than the stick-framed room. This alone illustrates how critical airtightness is to a building’s energy efficiency. The science behind air infiltration in framing products explains the key types of air movements and their effect on energy efficiency.
Air leaks through joints in sheathing and the inevitable gaps between lumber connections and between wood framing and the insulation. SIPs dramatically reduce air transfer within walls and roofs by minimizing these joints and by providing solid, continuous insulation across each panel’s height, width and depth.
SIPs can be manufactured up to 8′ x 24′ without joints in the OSB, whereas traditional stick-framed sheathing is typically only 4′ wide. Air can also leak through electrical and plumbing holes that are drilled in lumber studs.
The airtightness of a SIPs home has been repeatedly confirmed with blower door tests. In fact, Energy Star does not require a blower door test for SIPs homes to earn the Energy Star rating.
As warm air rises and cold air sinks in a conventionally framed wall cavity, a natural phenomenon called thermal or convective looping occurs, wasting valuable energy. Unless the insulation is a solid material to stop this air movement, it doesn’t matter what the insulation’s R-value is. What good is insulation if heat-carrying air can flow thought it and the cavities in the wall? SIPs’ solid insulation core helps eliminate this.
Thermal bridging occurs where there is a continuos element (such as studs within traditionally framed walls, and studs within traditionally framed walls, and stud-to-siding connections) between the cold and warm faces of a wall. These wood elements form a bridge between the inside and outside that can allow heat or cold to pass through by conduction. Simply installing R-19 batt insulation in a stick wall doesn’t mean the whole wall will have a R-19 R-value because there is still a significant amount of thermal bridging in traditionally framed stick walls.
Stick-framed buildings rely on lumber at regular intervals to provide structural support. 15-25% of the shell of a stick-framed home is lumber, compared to as little as 3% in the shell of a typical SIP framed home.
Whole Wall R-value (Energy Efficiency)
When all of these factors are considered, it makes sense that the ORNL’s whole wall R-value tests showed the following R-values for SIP versus stick-framed buildings:
Joe Pasma, PE, Premier SIPS Technical Manager