A detailed comparative study examines envelope systems in residential buildings made from mass timber, conventional construction and SIPs.

Editor’s Note: This is a summary of an academic paper that originally appeared in: Kurzinski, S., Mirzabeigi, S., and Riccitelli, B. (2025). “Comparative Performance Analysis of Mass Timber, Conventional, and SIPs Envelope Systems in Residential Buildings.”Mass Timber Construction Journal, 8(1), 1-11; iimag.link/XKOnd.

The building sector is a significant contributor to global energy consumption and greenhouse gas emissions, accounting for approximately 40 percent of the final energy demand and about 36 percent of emissions in the European Union. In the United States, residential housing accounts for about 21 percent of the total energy use, presenting a substantial opportunity for energy reduction through retrofitting solutions.

The research described in this article focuses on evaluating the lifecycle assessment (LCA), hygrothermal performance (i.e., of or relating to a combination of moisture and heat) using WUFI simulations, and thermal resilience of three distinct residential building envelope systems: 1) a conventional stick-built system with continuous insulation, 2) structural insulated panels (SIPs) and 3) a bio-based cross-laminated timber (CLT) system. These systems were selected based on their common applicability to the climate conditions and the sustainability demand of the materials.

Enhancing the thermal efficiency of building envelopes is crucial for reducing energy consumption and mitigating environmental impacts. The study focuses on optimizing the building envelope to improve thermal performance and reduce energy consumption, particularly in cold and humid climates.

Study Subjects

In this project, three different envelope wall systems were selected to showcase their differences and effectiveness in a residential setting. The first system, a conventional stick-built assembly with continuous insulation, is designed to provide continuous thermal insulation. This system typically includes layers such as exterior sheathing, a continuous insulation layer and an interior finish, all working together to enhance the building’s energy efficiency by minimizing thermal bridging and improving the overall thermal envelope.

The second system, SIPs, integrates an insulating foam-core sandwiched between two structural facings, typically the oriented strand board. SIPs are known for their high thermal performance and quick installation. This system includes the SIP panels, an exterior finish and an interior finish, providing a robust and energy-efficient wall assembly.

Figure 1. The layers and materials of (left to right) bio-based CLT, SIP and stick-built building envelopes.

The third system, a bio-based CLT wall, incorporates CLT panels and wool insulation with a cement exterior board. CLT is a sustainable building material made from layers of solid wood boards glued together at right angles, providing structural strength and stability. The wool insulation, made from natural fibers, enhances the thermal performance of the wall while offering environmental benefits such as reduced carbon footprint and improved indoor air quality. This system includes layers such as the CLT panels, wool insulation, a cement exterior board and an interior finish, creating a robust and sustainable wall assembly.

As shown in Figure 1 (above), each system’s unique composition and performance characteristics regarding sustainability, thermal performance and moisture penetration were analyzed to determine their effectiveness in wall section envelope applications. By comparing these systems, valuable insights were gained into their potential benefits and limitations, providing a comprehensive understanding of their applicability in residential envelope wall projects.

Key Findings

The study aimed to evaluate and compare the environmental impact, energy efficiency and moisture management of these three residential building envelope systems. A summary of key findings includes the following:

Environmental Impact

The study employed the Building Transparency Embodied Carbon in Construction Calculator (EC3) to evaluate the environmental impact of the building materials used in each envelope system. The EC3 tool is designed to analyze the embodied carbon, which includes the total greenhouse gas emissions associated with the production, transportation, installation, maintenance and disposal of these materials.

The LCA focused on stages A1-A5 of the building lifecycle, which encompass the product stage (A1-A3) and the construction process stage (A4-A5), which are critical for understanding the environmental footprint of the materials used in the envelope wall systems. The product stage includes raw material extraction (A1), transportation to manufacturing sites (A2), and the manufacturing process itself (A3). The construction process stage involves the transportation of materials to the site (A4) and the actual construction and installation activities (A5).

The study also compared the global warming potential (GWP) of each envelope wall system across these lifecycle stages. GWP is a measure of the total greenhouse gas emissions associated with the materials and processes used in each system. The results were presented in terms of both conservative and achievable GWP values. Conservative GWP reflects the inherent environmental impacts of the materials and manufacturing processes used in each system. Achievable GWP indicates potential reductions in GWP through sustainable practices such as carbon sequestration and advanced manufacturing technologies.

The bio-based CLT system demonstrated the lowest GWP compared to SIPs and the conventional stick-built system, highlighting the environmental benefits of using CLT, which supports carbon sequestration. The SIPs and conventional stick-built systems showed similar GWP values, indicating that both systems have room for improvement in terms of reducing their carbon footprints. The transportation impacts (stage A4) were also analyzed, with the SIPs system showing the lowest transportation-related GWP due to its lighter weight and efficient logistics.

By using the EC3 tool, the study provided detailed insights into the environmental impacts of the different envelope wall systems, enabling informed decisions to minimize the overall environmental footprint.

Moisture Management

The study employed WUFI Pro 6 to simulate moisture intrusion and mold growth among the three envelope wall assembly systems. WUFI VTT and BIO were also used for analyzing the moisture performance of building components, allowing for a detailed assessment of how different materials and assemblies handle moisture through time. The simulations were conducted considering the climate conditions of Bristol, R.I., which is classified under ASHRAE Climate Zone 5A that’s characterized by cold winters and warm, humid summers, making it essential to evaluate the assemblies’ ability to effectively manage moisture and prevent mold growth.

The study analyzed the initial water content and the rate of moisture loss and retention over a specified period. The ideal performance involves losing moisture quickly to prevent initial issues and then stabilizing to maintain long-term integrity and efficiency. The findings revealed significant differences in the moisture-management performance of the three systems:

Stick-built system:The stick-built system at stud demonstrated a moderate water-loss rate of 8.15 percent, indicating a relatively stable performance through two years. However, the stick-built system at the cavity, which utilized fiberglass insulation, exhibited an unusual increase in moisture content, resulting in a negative water loss rate of -8.08 percent. This suggests potential issues with moisture ingress or inadequate drying.

CLT envelope system:The CLT envelope system showed the highest rate of water loss at 23.24 percent, indicating significant drying over the two-year period. This suggests that the CLT system is more effective in managing moisture, reducing the risk of mold growth and moisture damage.

SIP envelope system:The SIP envelope system exhibited a high water-loss rate of 21.74 percent, reflecting substantial drying. This indicates that the SIP system is also effective in managing moisture by losing it quickly and then stabilizing.

The study conducted a mold growth test over a five-year period using WUFI VTT7. The findings revealed that among the three building envelope systems analyzed, only the stick-built system at the stud exhibited mold growth over the first five years of service. Although there was a very small amount of mold growth, it remained below the threshold for the risky mold index according to the ASHRAE 160 standard. The CLT and SIP systems did not show any mold growth, highlighting their effectiveness in preventing mold growth and maintaining indoor air quality.

The hygrothermal performance analysis demonstrated that the bio-based CLT system effectively managed moisture, reducing the risk of mold growth and moisture damage6. The SIP system also showed strong moisture-management capabilities, while the conventional stick-built system had higher moisture-retention risks. These findings underscore the importance of selecting appropriate building envelope systems to ensure long-term durability and indoor air quality.

Thermal Resilience

The study employed EnergyPlus to simulate the thermal resilience of the three envelope wall systems during a four-day heatwave and power failure in Bristol. The simulations aimed to understand how each system maintains indoor thermal stability under these disruptive events. The baseline building model was developed using the reference building model introduced by the U.S. Department of Energy. The building envelope characteristics were changed to create the three different envelope wall systems.

The study analyzed the thermal resilience of different envelope systems during the heatwave and power failure by examining the time-dependent thermal resilience curve for the living room zone. The post-processed time-series data illustrated how indoor operative temperatures evolved under the four-day power failure, emphasizing the impact of thermal mass and insulation.

SIP envelope system:Despite its high insulation (R=19.8), the SIP system exhibited rapid temperature spikes due to its low thermal mass, causing indoor conditions to quickly exceed habitable limits.

Bio-based CLT envelope system: Benefiting from higher thermal inertia, the CLT system demonstrated a delayed temperature rise and improved stability, staying within habitable levels for a longer duration (except during peak solar radiation hours).

Conventional stick-built system: Showed moderate performance, heating up faster than CLT but performing slightly better than the SIP system.

Overall, the bio-based CLT system provided the highest thermal resilience, maintaining lower indoor temperatures for a longer period during the blackout. This highlights the significance of incorporating thermal mass alongside insulation when designing buildings for extreme climate resilience. The findings support mass-timber construction as a viable passive design strategy to enhance occupant thermal comfort and reduce heat stress risks during power failures in hot conditions.

Conclusions and Further Research

The study findings highlight the critical role of material selection in optimizing energy efficiency, durability, and climate resilience in residential buildings. The bio-based CLT system demonstrated the lowest GWP and superior moisture regulation, losing water quickly and preventing mold growth. Its high thermal mass contributed to enhanced thermal resilience, maintaining stable indoor temperatures for longer periods during heatwave-induced power failures. However, its transportation emissions were higher due to logistical challenges.

The SIPs system offered high insulation value but exhibited rapid temperature fluctuations due to its low thermal mass, while the conventional stick-built system showed the highest moisture retention risk and moderate thermal resilience, with some mold growth detected in the fiberglass-insulated cavity.

These findings suggest that CLT is the most sustainable and resilient option among the selected envelope systems, though improvements in supply chain logistics could further reduce its environmental footprint. SIPs provide strong thermal insulation benefits, making them ideal for energy-efficient retrofits, while the conventional system remains viable but requires better insulation strategies to enhance long-term durability.

Future research should focus on long-term field validation of these envelope systems, hybrid wall designs that optimize both thermal mass and insulation, and cost-benefit analysis to assess large-scale adoption feasibility. Expanding resilience testing under various climate conditions will also provide deeper insights into year-round building envelope performance. This study reinforces the need for innovative, low-carbon building solutions to meet evolving sustainability and resilience demands. By integrating advanced envelope systems, the construction industry can significantly reduce energy consumption, improve occupant comfort and extend building lifespans, contributing to a more sustainable and climate-resilient built environment.