The quality of a building’s envelope is measured by the ability to prevent infiltration of outside air. Many prospective homeowners are familiar with the R-Value system that measures the insulation that goes into the new home. However, the stated R-Value doesn’t account for the wall’s actual thermal performance that may be affected by construction methods and time.
A comparison test by the Oak Ridge National Laboratory (ORNL) showed that a wall system using structural insulated panels is thermally very well designed. The testing compared a 4-inch SIP wall to both 2x4 and 2x6 stud walls at 16- and 24-inch spacing using fiberglass batt insulation. The tests concluded that the 2x6 frame wall filled with fiberglass labeled R-19 only achieved a whole-wall R-value of 13.7. The SIP test wall achieved a realistic whole-wall R-value of 14. The testing concluded that a 4” SIP wall provided 40% more thermal resistance than a 2x4 stud wall with an R-value of 9.6. A six-inch SIP panel results in an R-value of 21.6 in the same test comparisons.
Further testing demonstrated that the real performance is not the same as the rating of its insulation. About 15-25% of a stick wall’s areas consists of framing lumber. That lumber transmits heat at a much higher rate than the insulated cavities do. Wood framing in the wall create cold and warm zones on both the interior and exterior. Then, there are thermal short-cuts at corners and at joints where wall plates meet the floor or roof framing, means the actual insulating value may be cut by nearly a third.
Additional tests show that in worst case, but commonly found procedures for installing the batt insulation, the actual performance drops to R-11 as a result of installation imperfections.
In testing, SIPs have proven to be up to 50% more energy efficient. Under identical conditions, the room with 4-inch SIP walls used 9% less heating energy than the wood-framed room with 2x6 walls and R-19 fiberglass insulation.
A structural insulated panel provides the structural, insulating and air-sealing needed in wall, roof, floor and foundation systems. The panel is made by placing a foam core between oriented strand board. The panels are joined with splines, using foam sealant between all joints.
The ORNL performed tests on air flow in a 2x6 wood-framed and fiberglass-insulated wall compared to a SIP wall. Results showed that the SIP construction was 15 times more airtight than the wood-frame construction. The blower door test at 50 pascals of negative pressure showed 126 cubic feet of air per minute (cfm) leaking from the wood-framed room. The same blower door test on SIPS had an air leakage of 9 cfm. The same tests demonstrated the importance of properly sealing joints. When the joins are sealed properly, air infiltration and exfiltration is prevented. Moisture is also prevented from entering the building envelope, ensuring long-term durability.
SIP testing goes as far back as 1935 when the Forest Products Laboratory in Madison, Wisconsin first introduced the prototype. Their panels were used to build test homes that were disassembled and tested after thirty years to reveal that the panels retained their initial strength values.
Structural insulated panels provide a continuous air barrier as well as increased R-value when compared to traditional construction which means they can achieve energy-efficient and high-performance enclosures for new homes.