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Passivhaus Q&A Series: If Passivhaus is about keeping a building airtight, can the windows open?

This post is part of our series that shares questions we regularly receive about Passivhaus and low energy construction. We will be posting a new one every week. Explore our Blog to learn all about why designing buildings to low energy standards like Passivhaus delivers a lot more than just energy savings.


Passivhaus windows: cosy and open
Passivhaus windows: cosy and open

The Passivhaus, or Passive House, standard has garnered significant attention as an ultra-energy-efficient building approach. Central to its design philosophy is the concept of creating an airtight building envelope. This naturally leads many to question: does this mean that windows in a Passivhaus cannot be opened? Let's explore the relationship between airtightness and operable windows in the Passivhaus design.


The essence of Passivhaus:


The Passivhaus standard is a rigorous, voluntary standard for energy efficiency in a building. It was developed in Germany in the late 1980s and has since become an internationally recognised benchmark for sustainable architecture. The core goal is to reduce the building's ecological footprint by significantly minimising its energy requirements.


A key principle of the Passivhaus design is airtightness. Airtightness is essential for preventing unplanned heat transfer, mitigating moisture-related issues, and ensuring the effectiveness of mechanical ventilation with heat recovery. An airtight building minimises heat loss during cold months and heat gain during warmer periods. Consequently, this leads to reduced energy consumption for heating and cooling.


Windows in Passivhaus:


Windows play a crucial role in Passivhaus design. They're not just a source of natural light but also serve as a tool for passive solar gain. A common misconception is that the emphasis on airtightness implies that Passivhaus windows are sealed shut. This is not the case.


Windows in a Passivhaus are indeed designed to be exceptionally well-insulated and airtight when closed, but they can and do open. The purpose of the airtightness is to ensure that when windows and other openings are shut, there are no unintended drafts or air leakages. However, the ability to open windows is crucial for various reasons:

  1. Natural Ventilation: While Passivhaus buildings typically use mechanical ventilation systems to maintain indoor air quality, there are times when residents might want to introduce natural ventilation. On pleasant days, opening a window can offer fresh air, help to cool the space, and connect the indoors with the external environment.

  2. Overheating Prevention: During unusually hot periods, opening windows, especially during cooler nights, can help to purge excess heat from the building, reducing the risk of overheating.

  3. Occupant Comfort: Providing occupants with the ability to open windows can contribute to a sense of control over their environment, leading to enhanced wellbeing and comfort.

Quality and design matter:


While Passivhaus windows can open, it's crucial to recognise the importance of their quality and design. These windows are highly specialised. They usually have multiple layers of glazing, are filled with inert gases, and have insulated frames to minimise thermal bridges. Their design ensures that when they're closed, they seal tightly, maintaining the building's airtightness.


Conclusion:


The Passivhaus standard emphasises airtightness to achieve energy efficiency, but this doesn’t mean sacrificing the joy of an open window on a breezy day. Windows in Passivhaus buildings can and do open, merging the best of energy-efficient design with the comfort and flexibility desired by occupants. As with all aspects of Passivhaus design, the key lies in meticulous planning, high-quality materials, and expert execution, ensuring that when those windows shut, the building's energy-saving capabilities are in full swing.

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