The science behind Passivhaus

Passivhaus general | The 5 principles | The science behind Passivhaus


Airtight Construction

Mechanical Ventilation with Heat Recovery (MVHR)

High-Performance Windows and Frames

Eliminating Thermal Bridges

Optimized Solar and Internal Heat Gains

Rigorous Energy Modeling

Quality Assurance

Climate-Specific Design Strategies

Comfort and Indoor Climate Control


Thermal insulation is a cornerstone in the design of a Passive House (Passivhaus), playing a crucial role in minimizing heat transfer and ensuring energy efficiency. This article provides an in-depth analysis of the scientific principles behind thermal insulation within the Passive House standard, its importance, and the materials and strategies used to achieve optimal thermal performance.

A Passive House achieves remarkable energy efficiency by significantly reducing the need for active heating and cooling systems. Central to this achievement is the use of high-performance thermal insulation, which effectively reduces the rate of heat transfer between the interior and exterior of a building, thus maintaining a stable and comfortable indoor environment with minimal energy input.

Scientific Principles of Thermal Insulation:
Thermal insulation works on the principle of reducing heat transfer through conduction, convection, and radiation. In a Passive House, the insulation is part of a comprehensive system designed to minimize the building’s overall energy consumption for heating and cooling.

  1. Conduction: Insulation impedes the flow of heat through the building envelope.
  2. Convection: Properly installed insulation reduces air movement within the walls, preventing heat loss.
  3. Radiation: Reflective insulation can reflect radiant heat, contributing to thermal comfort.

Materials Used in Passive House Insulation:
A variety of materials can be used in Passive House insulation, each with its own thermal properties:

  1. Polyurethane Foam: Offers high R-values per inch and excellent air sealing properties.
  2. Cellulose: Made from recycled paper, it provides good thermal performance and sound dampening.
  3. Mineral Wool: Has fire-resistant properties and can be used for insulation and soundproofing.
  4. Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS): Both are types of rigid foam board insulation with different compressive strengths and moisture resistance.

Strategies for Implementing Thermal Insulation in Passive House Design:
Passive House design utilizes specific strategies to maximize the benefits of thermal insulation:

  1. Continuous Insulation: Avoids thermal bridging by ensuring there are no gaps in the insulation layer.
  2. Increased Insulation Thickness: Passive Houses often have much thicker insulation compared to conventional buildings.
  3. High-Performance Windows: Double or triple-glazed windows with insulated frames are used to complement wall insulation.
  4. Airtight Construction: Works in tandem with insulation to prevent heat loss through air leakage.

Importance of Thermal Insulation in Passive House:
Thermal insulation in a Passive House offers numerous benefits:

  1. Reduced Energy Consumption: By limiting heat transfer, insulation decreases the amount of energy needed for heating and cooling.
  2. Comfort: Consistent indoor temperatures are maintained, leading to increased occupant comfort.
  3. Durability: High-quality insulation can protect the building structure from temperature fluctuations and moisture.

Challenges and Considerations:
While insulation is essential, there are challenges to consider:

  1. Installation: Incorrect installation can reduce the effectiveness of insulation. Care must be taken to avoid gaps and compression.
  2. Moisture Management: Insulation must be accompanied by strategies to manage moisture to prevent mold growth and building deterioration.
  3. Material Selection: The environmental impact and sustainability of insulation materials are also important considerations.

The application of advanced thermal insulation is indispensable in the construction of a Passive House. It plays a pivotal role in achieving the ultra-low energy requirements characteristic of this standard. As the construction industry moves towards more sustainable practices, the principles utilized in Passive House insulation not only lead to significant energy savings but also pave the way for future innovations in building technology and design. With the continued emphasis on energy conservation and environmental responsibility, thermal insulation in Passive House design stands as a prime example of intelligent, sustainable construction that can be adapted and applied globally for a more energy-efficient future.

Airtight Construction

The Passivhaus standard represents the zenith of energy-efficient building design, with airtightness being a fundamental criterion. Airtightness in a Passivhaus plays a critical role in reducing energy consumption, mitigating unwanted air leakage, and ensuring a comfortable indoor climate. This article delves into the scientific principles of airtightness in the Passivhaus paradigm, exploring its importance, how it is achieved, and the resultant benefits.

The Passivhaus, or Passive House, design has set an international benchmark for energy efficiency, largely attributable to its stringent airtightness requirements. Airtightness is quantified by the number of times the total volume of air within a building is replaced through unintentional leakage per hour at a pressure difference of 50 pascals (n50 value). Passivhaus standards dictate an n50 value not exceeding 0.6 air changes per hour, a target far surpassing typical construction practices.

The Importance of Airtightness:
Achieving airtightness is paramount in Passivhaus design for several reasons:

  1. Energy Efficiency: Airtight buildings require significantly less energy to heat and cool, as the loss of conditioned air is minimized.
  2. Thermal Comfort: With reduced air infiltration, there are fewer cold drafts, resulting in a more consistent and comfortable indoor temperature.
  3. Moisture Control: By controlling air leakage, airtightness also regulates moisture ingress, which can prevent mold growth and structural damage.
  4. Acoustic Insulation: Airtightness contributes to noise reduction, as gaps and cracks that allow air to pass through can also transmit sound.

Achieving Airtightness in Passivhaus Design:
Airtightness is achieved through meticulous design and construction practices, which include:

  1. Careful Planning: From the onset, architectural plans must detail the air barrier and consider continuity at all joints and interfaces.
  2. Quality Materials: Specialized materials such as membranes, sealants, and tapes are employed to create an uninterrupted air barrier.
  3. Skilled Workmanship: Proper installation of materials is crucial and often requires workers trained in Passivhaus construction techniques.
  4. Blower Door Testing: This diagnostic tool is used both during and after construction to detect leaks and verify that the airtightness criterion is met.

Benefits of Airtightness:
The benefits of airtight construction are extensive and include:

  1. Lower Heating/Cooling Loads: Airtightness reduces the building’s heating and cooling demand, leading to lower operational costs.
  2. Enhanced Durability: By preventing moisture-laden air from entering the building envelope, airtightness prolongs the life of building components.
  3. Improved Indoor Air Quality: With a controlled ventilation system, indoor air quality is significantly improved as the introduction of pollutants from outside is reduced.
  4. Environmental Impact: The reduced energy demand directly translates into lower carbon emissions, contributing to environmental sustainability.

The principle of airtightness is an integral component of the Passivhaus design, which ensures exceptional energy performance and occupant comfort. Through the strategic application of building science and meticulous construction practices, airtightness not only aligns with stringent energy efficiency goals but also exemplifies a commitment to sustainable building practices. As the Passivhaus standard continues to gain traction globally, the emphasis on airtightness sets a new precedence in the construction industry, forging a path toward a more energy-independent and ecologically conscious future.

This focus on airtightness is particularly essential in a world where energy efficiency and sustainability are not merely aspirational goals but imperative requirements for the betterment of our environment and society.

Mechanical Ventilation with Heat Recovery (MVHR)

Mechanical Ventilation with Heat Recovery (MVHR) systems represent a pivotal technology in Passivhaus construction, optimizing energy efficiency while maintaining superior indoor air quality. This article investigates the functionality of MVHR systems within the Passivhaus standard, exploring their role, benefits, and the science underlying their operation.

The incorporation of Mechanical Ventilation with Heat Recovery is a defining feature of the Passivhaus standard, facilitating a constant supply of fresh air without the thermal losses typically associated with ventilation in conventional buildings. The MVHR systems are engineered to recover heat from exhausted indoor air and transfer it to the incoming fresh air, significantly reducing the energy demand for space heating and cooling.

Operational Principles of MVHR:
MVHR systems consist of two airflow streams: exhaust air from the interior and fresh incoming air from the exterior. These streams flow through a heat exchanger, where heat from the warmer exhaust air is transferred to the cooler incoming air. This heat exchange process is facilitated without mixing the two air streams, thereby conserving energy that would otherwise be lost.

Core Components:

  1. Heat Exchanger: The central unit where heat transfer occurs, typically a counter-flow or cross-flow heat exchanger.
  2. Ductwork: A network of insulated ducts that deliver fresh air to and extract stale air from the building.
  3. Filters: To ensure air quality, filters remove particulates and pollutants from incoming air.
  4. Fans: Low-energy fans are used to move air through the system efficiently.

Importance in Passivhaus Design:
The MVHR system is integral to the Passivhaus concept due to several key factors:

  1. Energy Conservation: By recovering heat from exhaust air, the energy requirement for heating new incoming air is significantly reduced.
  2. Comfort: Consistent indoor temperatures and humidity levels are maintained, enhancing occupant comfort.
  3. Air Quality: Continuous filtered ventilation ensures a supply of clean air, which is particularly beneficial in urban areas with high pollution levels.

Benefits of MVHR in Passivhaus:

MVHR systems offer multifaceted benefits:

  1. Energy Savings: MVHR can recover up to 90% of the heat from exhaust air, thereby reducing the energy needed to heat the building.
  2. Reduction in Carbon Footprint: Lower energy consumption directly correlates to reduced greenhouse gas emissions.
  3. Healthier Living Environments: Enhanced air quality reduces the risk of respiratory issues and contributes to the overall well-being of occupants. Energy and Heat Recovery Ventilation

Challenges and Solutions:
While MVHR systems are highly efficient, they require careful design and installation:

  1. Balancing Airflows: Ensuring that the supply and extract air volumes are balanced is crucial for system efficiency.
  2. Noise Minimization: Adequate silencing features and strategic ductwork design are necessary to prevent noise transfer.
  3. Maintenance: Regular maintenance of filters and the heat exchanger is essential to maintain system performance and air quality.

MVHR systems in Passivhaus construction are a testament to the harmonious balance between environmental sustainability and the creation of healthful living spaces. They epitomize the Passivhaus commitment to energy efficiency without compromising indoor air quality or occupant comfort. As the focus on sustainable building grows, MVHR technology stands out as a cornerstone in the design of energy-efficient buildings that also prioritize the health and well-being of their inhabitants. The integration of MVHR in Passivhaus design is not just a feature of high-performance buildings but a necessary step towards a more sustainable and conscientiously built environment.

High-Performance Windows and Frames

In the realm of Passive House (Passivhaus) standards, windows and doors are far more than mere access points; they are sophisticated components integral to the building’s thermal performance and energy efficiency. This article elucidates the rigorous requirements for windows and doors in a Passive House, detailing their design, function, and the critical role they play in maintaining the delicate energy balance within these highly insulated and airtight structures.

A Passive House is a meticulously designed construct that drastically reduces the ecological footprint by utilizing passive solar building design and superinsulation to minimize the need for active heating and cooling. Within this framework, windows and doors are key elements that contribute to the Passive House’s overall thermal envelope, allowing for light and interaction with the outside while preserving the energy integrity of the building.

Scientific Principles of Windows and Doors in Passive House Design:
Windows and doors in a Passive House are engineered to achieve superior thermal performance through the following principles:

  1. Glazing: Multiple layers of glazing with gas fills such as argon or krypton enhance the thermal resistance of windows.
  2. Spacers: The use of warm-edge spacers between panes reduces heat transfer and prevents condensation.
  3. Frames: Highly insulated frames with thermal breaks limit heat loss and prevent thermal bridging.
  4. Orientation: Strategic placement harnesses passive solar gain while minimizing overheating risks.

Design and Construction Aspects:
Passive House windows and doors must adhere to rigorous specifications:

  1. U-values: The U-values for these components are typically below 0.8 W/(m²K), indicating their high insulating ability.
  2. Airtightness: They are installed with precision to ensure airtight seals, crucial in maintaining the building’s overall energy performance.
  3. Durability: Materials and construction are chosen to withstand the test of time while maintaining their insulating properties.
InVitra centre seal passive house – WA15/2 | Kömmerling

Role in Passive House Energy Balance:
Windows and doors are crucial for the following reasons:

  1. Energy Efficiency: They contribute significantly to reducing the heating demand to the Passive House threshold of 15 kWh/(m²yr).
  2. Comfort: By eliminating cold drafts and providing consistent indoor temperatures, they ensure occupant comfort.
  3. Natural Light: They facilitate ample daylight, reducing the need for artificial lighting.

Challenges in Integration:
Incorporating high-performance windows and doors requires addressing several challenges:

  1. Cost and Availability: The higher initial cost and sourcing of appropriate products can be a barrier.
  2. Installation Expertise: Proper installation by trained professionals is essential to realize the benefits of these high-tech components.
  3. Balancing Gains and Losses: It’s important to balance solar gains through windows with potential heat losses, especially in different climates.

Windows and doors are not mere peripherals but are central to the Passive House design ethos, representing the synergy of functionality, energy efficiency, and comfort. They are powerful allies in the quest to reduce energy consumption, greenhouse gas emissions, and to provide durable, comfortable, and sustainable living spaces. As the Passive House standard continues to gain traction globally, the development and refinement of windows and doors will remain a key focus for innovators and manufacturers alike. The future of building design hinges on such advancements, pushing the boundaries of what is possible in energy-efficient construction and setting new benchmarks for the industry at large.

Eliminating Thermal Bridges

Thermal bridging is a pivotal concern in the architectural integrity of Passive House (Passivhaus) standards, as it can significantly undermine the thermal efficiency of a building. This article explores the concept of thermal bridges, their impact on Passive House design, and the strategies employed to mitigate their effect, thereby ensuring the thermal envelope’s continuity and performance.

Passive House represents the zenith in low-energy building standards, necessitating meticulous attention to detail to prevent heat loss. Thermal bridging, an area within the building envelope that has a significantly higher heat transfer rate than the surrounding materials, is a critical factor that can compromise the insulative properties of a building. By understanding and addressing thermal bridges, Passive House designers can drastically reduce unnecessary heat loss and optimize the building’s energy efficiency.

Scientific Explanation of Thermal Bridging:
A thermal bridge occurs when materials with poor insulating properties allow an easy pathway for heat flow across a thermal envelope, leading to increased heat loss in winter and heat gains in summer. These can be categorized as follows:

  1. Structural Thermal Bridges: Occur where the building structure penetrates the insulation layer, e.g., at floor and wall junctions.
  2. Material Thermal Bridges: Arise when materials with different thermal conductivities come into contact, allowing for heat transfer.
  3. Geometric Thermal Bridges: Result from the shape or geometry of the building itself, such as corners or edges where the area of heat loss is greater.

Passive House Approach to Thermal Bridging:
The Passive House standard necessitates a comprehensive approach to mitigating thermal bridges:

  1. Thermal Bridge Free Construction: This involves designing details where there is continuous insulation across all junctions.
  2. Thermal Modeling: Utilizing software to predict where thermal bridges may occur and to quantify their impact.
  3. Innovative Materials: Employing advanced insulating materials and construction techniques to interrupt heat flow.
  4. Quality Assurance: Rigorous onsite verification ensures that the construction matches the thermal bridging-free design.

Impact on Energy Performance:
Thermal bridges can lead to:

  1. Increased Energy Consumption: They can account for a significant portion of a building’s heat loss, leading to higher energy use for heating and cooling.
  2. Condensation Risks: They can cause surface temperatures to drop below the dew point, leading to condensation, mold growth, and structural degradation.
  3. Comfort Issues: Cold spots can occur, leading to discomfort for the occupants.

Mitigation Strategies in Practice:
Effective strategies to mitigate thermal bridges include:

  1. Insulated Structural Components: Using materials such as insulated concrete forms or structural insulated panels.
  2. Thermal Breaks: Inserting materials with low thermal conductivity into the structure to interrupt heat flow.
  3. External Insulation: Wrapping the building envelope with continuous insulation to cover potential thermal bridges.

In the quest for achieving the Passive House standard, the meticulous management of thermal bridges is essential. It requires a synergy of advanced materials, innovative design, and precision in execution. Addressing thermal bridging effectively enhances building durability, occupant comfort, and energy efficiency. As the building industry evolves towards more sustainable practices, the lessons learned from Passive House design in mitigating thermal bridges will influence wider construction methodologies, fostering a future where buildings are not only energy-efficient but holistically designed to minimize their environmental impact.

Optimized Solar and Internal Heat Gains

The Passivhaus design takes a proactive approach to harnessing the sun’s energy. Through careful planning and strategic placement of windows and shading devices, buildings are positioned to take advantage of the sun’s path for passive solar heating when necessary and to prevent overheating during warmer periods. This balance ensures that natural resources are utilized efficiently, contributing to the heating needs in colder months and preventing excess heat during warmer times.

The PHPP software is used to calculate the precise amount of solar heat gain required to maintain comfort based on window orientation, shading, and local weather patterns. It also accounts for internal gains from people, electronics, lighting, and appliances, reducing the need for external energy input.

Rigorous Energy Modeling

The application of the PHPP or equivalent energy modeling tools in Passivhaus design isn’t just about adhering to a certification; it’s about understanding the minute details of how a building will perform. This includes accounting for all forms of heat transfer, ventilation dynamics, and thermal mass impacts. The modeling is comprehensive, encompassing every element of the building’s design, from the thermal characteristics of materials to the impact of occupants and their activities.

Quality Assurance

In a Passivhaus project, quality assurance is an ongoing process, not a final check. It starts with the design and continues throughout construction, with meticulous inspections, testing, and adjustments. This ensures that the building not only meets the theoretical specifications but also operates as intended in real-world conditions. Post-occupancy evaluations are often conducted to monitor performance and provide feedback for future projects.

Climate-Specific Design Strategies

Design strategies are adapted to climate specifics, such as high levels of insulation and south-facing windows for cold climates, or strategic shading and natural ventilation for warmer climates. Every design decision is made with the local weather patterns and environmental conditions in mind to optimize for energy efficiency and comfort.

Comfort and Indoor Climate Control

Passivhaus design prioritizes the indoor thermal environment. The standard aims to keep the temperature differential between air and surfaces within 4.5°C. It also requires that temperatures do not exceed 25°C for more than 10% of the hours in a year (for most climate zones), which is achieved without conventional heating or cooling systems.


By integrating a meticulous design approach with robust scientific principles and advanced technologies, the Passivhaus standard creates buildings that are exemplary in their energy efficiency, comfort, and sustainability, making them a responsible and economically prudent choice for the future of construction.

The scientific approach of Passivhaus is not just about the energy though; it’s about creating buildings that are supremely comfortable, affordable to maintain, and have a minimal ecological footprint. The rigorous application of building physics ensures that once a Passivhaus is constructed, it will perform to the highest standards of efficiency and comfort for its entire lifespan.