To ensure optimal system performance, special attention must be given to the design of high-performance opaque building envelope. Building envelope technologies account for approximately 30% of the total energy consumed in commercial buildings.1 Optimizing the opaque envelope is crucial for reducing energy consumption, while also improving occupant health and comfort by maintaining consistent temperatures and ensuring good air quality. This technical guide will cover the essential components of the high-performance opaque building envelopes, including walls, roofs, floors and provide strategies to enhance their energy efficiency.
What is a High-Performance Opaque Building Envelope?
A building’s opaque envelope consists of the walls, roof, and foundation, essentially all elements of a building’s envelope excluding windows, creating the boundary between interior and exterior environments.
A high-performance opaque envelope focuses on optimizing these elements to maximize energy efficiency and minimize waste. Key strategies include using high-quality continuous insulation in walls and roofs, thermal bridging mitigation, moisture control layers, exterior sheathing, and sealing gaps airtight to prevent air leaks. These measures help ensure a more energy-efficient and comfortable indoor environment by achieving optimal thermal performance and preventing air infiltration while managing moisture levels within wall assemblies.
Key Components
1. Continuous Insulation
Insulation is a critical aspect of a high-performance building envelope. While fiberglass insulation is commonly used in new construction, the installation technique in which the insulation is applied matters just as much as the type. Proper continuous insulation ensures maximum efficiency. Insulation is absolutely critical to achieving a high-performance building envelope, as it plays a central role in minimizing heat loss and gain, thereby significantly impacting energy efficiency, indoor comfort, and overall building performance by maintaining stable indoor temperatures.
Insulation levels are measured by R-value, which indicates the material’s resistance to heat flow. A higher R-value means greater insulation performance and energy efficiency. The optimal R-value can vary depending on climate zone and building type. For instance, colder climates typically call for higher R-values to minimize heat loss, while milder climates may have lower R-values.
Properly insulating different parts of the building, such as walls, floors, and roofs, with appropriate R-values is critical to maintaining energy efficiency and reducing heating and cooling costs.
2. Air Sealing
Envelope air leakage can significantly impact a building’s energy efficiency by allowing unwanted heat loss in colder climates or heat gain in warmer climates through gaps in the building envelope. These air leaks undermine the insulation’s ability to maintain a consistent indoor temperature, leading to increased heating and cooling demands. Additionally, air leakage contributes to condensation by allowing warm, moist indoor air to escape through gaps, encountering cooler surfaces and condensing. To prevent these issues, it’s essential to seal cracks and gaps with continuous air barriers, weatherstripping, and caulk. While it’s nearly impossible to eliminate all air leakage, addressing these critical areas can significantly improve energy efficiency by reducing thermal loss or gain and minimizing moisture-related problems.
3. Vapor Barrier
A vapor barrier is a layer designed to prevent moisture movement within the wall assembly. By controlling moisture, it helps protect against mold growth and enhances energy efficiency, particularly by reducing heat loss associated with condensation. This layer is typically made from impermeable materials, with the choice depending on climate, building requirements, and building codes. The vapor barrier is installed on the warm side of the insulation within the wall assembly. This side varies between warm and cold climates due to differences in moisture movement in those environments.
4. Thermal Bridging Mitigation Strategies
Thermal bridging occurs when heat escapes through weak points in the building envelope, often at gaps in the insulation layer, or when materials with different thermal conductivity levels come into contact. Structural elements like metal framing commonly contribute to thermal bridging, which can reduce insulation effectiveness, creating cold spots on walls and ceilings, leading to condensation, and significantly increasing heat loss. These factors raise energy consumption, forcing the HVAC system to work continuously and driving up operational costs.
Thermal Bridging Can be Categorized into Two Types:
- Linear thermal bridges occur at continuous connections, such as where walls meet roofs, foundations, or window and door openings. To prevent thermal bridging in these areas, continuous insulation is often required. Special attention must be given to the design and placement of insulation at these junctions to minimize heat transfer.
- Point thermal bridges are smaller and occur at localized points, such as fasteners or exposed metal elements. These areas must be carefully addressed to prevent heat transfer.
5. Weatherproofing
When selecting materials for a building, it’s crucial to account for the climate zone. California’s diverse climate zones present varying weather conditions, which directly impacts the insulation requirements of a building among other elements like weatherproofing. Key factors include moisture levels, temperature fluctuations, and average wind loads specific to the building’s location. Choosing durable and weather-resistant materials for exterior walls, roofs, and other envelope components is essential to ensure long-term performance.
Optimizing Building Orientation
Additionally, building orientation plays a significant role in energy efficiency. Orient longer buildings east-west to consistently harness or avoid thermal gain along the long face. This orientation minimizes the area that’s subject to faster energy swings from the rising or setting sun. Optimizing the building’s orientation is key to maximizing passive solar gains and minimizing heat gains from direct sunlight.
An efficient building envelope helps maintain consistent indoor temperatures, reducing the load for heating and cooling. As a result, this can lower the size and cost of the HVAC system. Together, the building envelope and HVAC system work in tandem to ensure stable temperatures for optimal indoor comfort.
What Are the Benefits?
- Heating and cooling loads are reduced resulting in a more energy-efficient building.
- A good building envelope keeps indoor temperatures consistent and comfortable and enhances air quality by keeping pollution out.
- Greenhouse gas emissions are lessened by cutting energy use.
- The building’s temperature is better maintained, leading to lower energy costs.
- Advanced materials and designs improve longevity, minimize structural stress, and decrease upkeep needs, resulting in a more resilient building.
- A well-constructed high-performance envelope can contribute to improved sound insulation within a building.
- High-performance envelopes can help prevent moisture infiltration, reducing the risk of mold and mildew growth within the building.
What Are the Challenges/Constraints?
- Upfront costs are likely increased because of the use of advanced materials and technologies.
- Requires more specialized knowledge and skills for proper design and installation.
- Enhanced insulation and air-sealing measures might require additional space within walls and other building components.
- Integrating high-performance envelopes with existing systems can be challenging.
- Design challenges with integrating complex building geometries with high-performance envelope strategies can potentially require advanced modeling and analysis tools.
- Balancing high-performance envelope strategies with architectural aesthetics can pose challenges in maintaining the desired building appearance.
- Effective integration of the building envelope design with HVAC systems, lighting, and other components is crucial for maximizing overall energy performance and requires careful coordination.
- Selecting insulation materials with high R-values while considering factors like weight, moisture resistance, durability, and environmental impact.
Who is Eligible for Inducements?
This inducement is available for projects implementing high R-value exterior walls, roofs, slabs, and exposed floor assemblies, and taking prescriptive steps to mitigate thermal bridging. These measures can minimize heating and cooling losses through the envelope, thus reducing energy use and carbon emissions.
- Minimum Effective Insulation Requirements (applicable to all CA climate zones):
- Thermal Bridging Requirements: Projects must meet the prescriptive criteria for thermal bridging outlined in ASHRAE Standard 90.1 (2022), Section 5.5.5, which covers both linear and point thermal bridges.
- Project team agrees to provide the following insight and documentation regarding this measure:
- Envelope design details, including thermal bridging
- Implementation cost data
- Results from any relevant analyses
- Criteria for measure selection
- Summary of design or construction challenges
- Participate in on-site verification and possible data logging of the system
- Project may be selected by PG&E for a future case study
Contact us today to enroll and build resiliency into your project.
Resources:
1. Better Buildings Initiative. (n.d.). Building envelope. U.S. Department of Energy. Building Envelope
2. U.S. Department of Energy. (n.d.). Vapor barriers. Building Science Education. Vapor Barriers
3. ClimaSpec. (2024, January 2). ASHRAE thermal bridging. ASHRAE 90.1-2022 Thermal Bridging: Increased Energy Efficiency
4. Kingspan. (2023, February 13). What is thermal bridging? What is Thermal Bridging
5. Green Girt. (2024, September 4). ASHRAE 90.1–2022: Thermal bridging updates. A2P1097: Meeting and Exceeding Energy Code Requirements in ASHRAE 90.1-2022 – Recognizing Impact: Thermal Bridging
6. Rise. (2021, June 23). Thermal bridging: What it is and how to prevent it. Thermal Bridging and How to Reduce It
