Unlocking High-Performance Building: Key Terms and Concepts Explained

In this article, we'll dive into the essential terms and concepts that define often referenced in the high performance building world. From air tightness to thermal bridging, we'll explore the building blocks of healthier, more resilient structures.

Air Tightness: Air tightness measures how much air leaks through a building envelope. A tightly sealed building minimizes air leakage, preventing heat loss and improving energy efficiency. It also prevents insects from entering the building, and helps maintain indoor air quality by keeping pollutants and moisture out, increasing health and reducing the risk of mold and rot.

Building Envelope: The building envelope is like the skin of a building, separating its interior from the exterior environment. It includes walls, windows, roofs, and foundations, as well as the joints between these elements. A well-designed building envelope regulates heat, air, moisture, solar radiation, insects, and noise, ensuring comfort and durability.

Continuous Insulation: The structural wood or metal framing in any building can transfer heat and cold, making it less energy efficient. This sneaky heat or cold transfer is called "thermal bridging." By adding a layer of continuous insulation over the framing (studs and cavities), the thermal bridging is reduced.

Dew Point: The dew point is the temperature at which water vapor in the air begins to condense into liquid water. In buildings, understanding the dew point is crucial because it indicates areas where condensation may occur, potentially leading to mold growth and other moisture-related issues. For instance, if insulation is improperly installed inside a wall, it can create a dew point between the insulation and the wall surface, increasing the risk of condensation buildup and subsequent mold growth. Proper management of dew points is essential for maintaining indoor air quality and preventing moisture-related damage in buildings.

Ductless Mini-Split (DMS): A DMS is a heating and cooling system that doesn't require ductwork to distribute air. Instead, it consists of an outdoor compressor unit connected to one or more indoor units. DMSs are incredibly energy-efficient, allowing for personalized comfort and lower energy bills.

Grid-tied: Grid-tied refers to a building or system that is connected to the public utility grid for electricity supply. Grid-tied buildings can generate their own power through renewable sources like solar or wind, with any excess electricity being sold back to the grid. This setup allows for energy independence while still having access to grid power when needed.

Heat Recovery Ventilator (HRV/ERV): An HRV (Heat Recovery Ventilator) is a mechanical ventilation system that exchanges stale indoor air with fresh outdoor air while recovering heat from the exhaust air. In addition to just sensible energy recovery (heat), an ERV (Enthalpic Recovery Ventilator) also recovers latent energy (humidity). HRVs and ERVs help maintain good indoor air quality while minimizing energy loss, making them essential components of high-performance buildings.

High Performance Windows: High performance windows are designed to minimize heat transfer, enhance energy efficiency, and improve comfort levels within a building. These windows utilize advanced technologies and materials to provide superior insulation, reduce air leakage, and mitigate thermal bridging. Common technologies are thermally broken components, dual or triple-pane windows filled with argon or krypton gas (depending on climate), and Low-E (Low-emissivity) coatings. 

Off-grid: Off-grid describes a building or system that operates independently of the public utility grid. Off-grid buildings generate and store all the energy they need on-site, typically through renewable sources like solar panels and wind turbines. Off-grid living requires careful energy management and storage to ensure uninterrupted power supply.

R-value/U-value: R-value (thermal resistance) and U-value (thermal transmittance) are measurements used to assess the thermal performance of building materials, and they have a direct, inverse relationship. R-value measures a material's resistance to heat flow, with higher values indicating better insulation. U-value, on the other hand, measures the rate of heat transfer through a material, with lower values indicating better insulation. Both values are crucial for determining efficiency of building components.

Solar PV: Solar PV (photovoltaic) panels convert sunlight into electricity, to reduce reliance on grid electricity and fossil fuels, making them key components of sustainable building design.

Thermal bridge: A thermal bridge is a pathway for heat to flow through a building's envelope, typically where two materials with different thermal properties meet. Thermal bridges can result in localized heat loss, condensation, and increased energy consumption. Preventing thermal bridges through proper design and insulation is essential for maintaining thermal comfort and energy efficiency.

Wind Barrier: A wind barrier is a membrane that acts like a shield to protect vapor open continuous insulation from exposure to wind. Walls without a wind barrier can lose 34-45% of their effective R-value in windy conditions. Wind barriers are still relatively unknown in the High Performance building world. 

WRB (Water-Resistive Barrier): Imagine a raincoat for a building. Just like you wear a raincoat to stay dry when it's raining, a WRB is like a protective layer for the outside of a building. It's usually a material that goes underneath the siding or exterior finish of a building. Its job is to stop water from rain or snow getting inside the walls. If water gets inside, it can cause all sorts of problems like mold, rot, and damage to the structure of the building. So, a WRB is really important for keeping buildings safe and dry.

Vapor Permeability: Despite our best efforts, liquid water and water vapor can make its way into the wall assemblies. Opting for vapor-open insulation and vapor-open WRB and air membranes allows water vapor to move through the building materials so that the wall can dry effectively.  Many traditional building materials can act as vapor barrier, trapping and moisture within the walls, leading to rot and mold. 

To learn the key concepts of performance building, see our guide: High Performance Building: A Beginners Guide to the Five Fundamentals.

For more on the benefits of high performance building, see our guide: The Benefits of High Performance Building: A Science Based Approach to Design and Construction