What is Airtightness and Why is it Important in a Passivhaus?
Passivhaus construction places a strong emphasis on airtightness — a fundamental principle that ensures structural durability while increasing energy efficiency and occupant comfort. It signifies a holistic approach to building design that supports thermal performance, durability, sustainability and occupant comfort.
Picture a leaky refrigerator, for example. Without the necessary level of airtightness, your refrigerator would struggle to maintain adequate temperatures, causing additional issues later down the track, like a mouldy seal. To fix this, you wouldn’t add extra insulation or bolt on a renewable power source. Instead, you’d go straight to the problem and fix the leak.
The same happens with our buildings, and this is why an airtight building envelope is vital for optimal and cost-effective outcomes rather than relying on band-aid fixes, like additional insulation or solar.
In this article, we delve into the Passivhaus principle of airtightness, its impact and application on-site as well as the various benefits, mistakes and misconceptions around airtightness.
What is airtightness?
At its core, airtightness involves crafting a building envelope that minimises uncontrolled air movement, ensuring efficient heat retention and reducing reliance on traditional heating systems. Passivhaus buildings achieve this through strategic air barrier placement tailored to various climates.
Achieving a high level of airtightness is crucial as it significantly reduces the size of conventional heating and cooling systems needed to ensure comfortable indoor temperatures once heat recovery ventilation is installed. But contrary to popular belief, Passivhaus focuses on optimising thermal comfort for occupants, rather than energy efficiency in and of itself.
“If we aim for thermal comfort and a durable building envelope, energy efficiency will come with it as a consequence, rather than working the other way around.”
-Scott Stewart, Principal Passivhaus Designer @ LAB Design and APA Trainer.
A continuous air barrier also significantly contributes to the durability of the building envelope as there are fewer chances for moisture ingress which can degrade the building, improving the lifespan of the building.
While achieving an air change rate as close to zero as possible would be ideal for thermal performance, it can be economically challenging. That’s why, based on comprehensive cost-benefit analyses, the recommended level of airtightness in Passivhaus must be ≤ 0.6 air changes per hour (ACH) @ 50 Pascals of pressure. For retrofit projects, the 0.6 ACH goal is the same, however, there is extra leniency of up to 1 ACH, if steps are being taken to improve airtightness.
Benefits and misconceptions about airtightness
Airtightness plays a crucial role in Passivhaus construction, offering numerous benefits when implemented correctly. However, there are also common misconceptions that can lead to misunderstandings about the importance and practical implications of airtightness in building design.
Benefits of airtightness
1. Condensation and Moisture Control: Proper airtightness helps manage condensation and moisture within the building envelope. By minimising air leakages, the risk of moisture-related issues such as mould growth and structural degradation are significantly reduced. Thus, contributing to the long-term durability and health of the building.
2. Energy Efficiency: Airtightness is fundamental to achieving high levels of energy efficiency in Passivhaus buildings. By reducing air infiltration and heat loss, airtight structures require less energy for heating and cooling, leading to lower energy bills and reduced environmental impact.
3. Sound Insulation: Airtight buildings tend to be quieter due to the disruption of sound wave paths through insulation and air barriers. This creates a calm and comfortable indoor environment for improved sleep and relaxation.
4. Vermin and Dust Control: Airtight buildings are less susceptible to vermin, dust, and dirt infiltration. With no unintended gaps for entry, the indoor environment remains cleaner and healthier. This is particularly noticeable in the ceiling areas of a building.
5. Improved Indoor Air Quality: Airtight buildings don’t equal stale buildings. Instead, Passivhaus buildings rely on mechanical ventilation systems to maintain optimal indoor air quality. This controlled ventilation ensures a constant supply of fresh air while expelling stale air, reducing the buildup of CO2 and other pollutants. In contrast, although code homes tend to have a lot of air leakage and infiltration, it still results in much higher CO2 levels when compared to the precise ventilation of a Passivhaus.
6. Reduced Environmental Impact: Improved airtightness not only reduces energy consumption but also contributes to a smaller carbon footprint. Passivhaus buildings with exceptional airtightness can achieve remarkable levels of environmental sustainability due to not having significant cooling or heating demand. As an aside, Passivhaus’ also tend to be built with more sustainable materials, further reducing environmental impact.
Misconceptions about airtightness
1. Buildings Need to "Breathe": One common misconception is that buildings should be allowed to "breathe" to maintain healthy indoor air quality. In reality, if building membranes are used, the building fabric may need to "perspire", but it’s the people inside who need to breathe. That’s why mechanical ventilation systems serve as the "lungs" of the building, ensuring adequate fresh air intake while managing humidity levels far better than buildings built to minimum code. Although, some Australian climates may require dedicated dehumidification as well.
2. Risk of Indoor Air Quality Issues: While mechanical ventilation is key in maintaining good indoor air quality, a Passivhaus will still have sufficient air supply and quality even if there are overnight power outages. For some extra peace of mind, occupants can also open their windows if this issue ever occurs.
3. Maintenance and Perforations: As long as the building envelope isn’t disturbed ongoing maintenance isn’t necessary. Instead, homeowners should be extra careful when installing anything that hangs on the wall as plasterboard screws and other installations can inadvertently puncture the air barrier. If this occurs, it’s important to repair it quickly as even tiny holes can lead to condensation, reducing the durability of the envelope.
4. Misalignment of Priorities: Some may mistakenly prioritise energy efficiency over thermal comfort and durability. In Passivhaus design, achieving thermal comfort and durability through airtightness and insulation leads to enhanced energy efficiency as a natural consequence.
5. You Shouldn’t Open Windows in an Airtight Building: The truth is, if it’s a nice day outside, you absolutely can open your windows! However, it’s often the case that opening the house to the exterior conditions is not ideal, such as when it’s too hot, cold, polluted or noisy, for example. During these times, your heat recovery ventilation will do the hard work of ensuring your building temperature is comfortable and your indoor air is clean and healthy.
While airtightness offers numerous benefits in Passivhaus construction, it is essential to address common misconceptions to ensure successful implementation. By understanding the role of airtightness in managing moisture, enhancing energy efficiency, improving indoor air quality, and promoting durability, stakeholders can appreciate its significance and achieve optimal building performance in Passivhaus projects.
The application of airtightness in Passivhaus
In Passivhaus construction, airtightness is crucial for ensuring the long-term durability and performance of the building envelope.
The air barrier, which forms a critical part of this strategy, can serve as a protective shield that preserves the integrity of the insulation (depending on where the barrier is placed) and safeguards occupants from potential issues arising from moisture ingress and air leaks.
In colder climates, such as Europe, the air barrier is typically positioned on the warm side of the insulation. This prevents warm, moist air from escaping and condensing within the insulation layer, which could lead to reduced thermal performance and potential structural issues like timber rot and mould growth.
However, in regions like Australia, where external moisture intrusion can be a concern due to varying climatic conditions, air barrier placement may involve a combination of interior and exterior barriers or integration with the weatherproofing layer.
Mistakes when adhering to airtightness standards
Adhering to airtightness standards in Passivhaus construction requires careful planning and execution.
However, several common mistakes can occur during the design and construction process that may compromise the effectiveness of the air barrier and overall building performance.
1. Late Consideration of Airtightness: Some architects and building designers may overlook the difficulty of achieving airtightness on-site, leading to design elements that create challenges during construction, such as complex junctions or areas susceptible to air leaks. To avoid this, it’s important for Passivhaus Tradespeople to be involved in the early stages of building design. “Don’t wait for the frame to go up before you start thinking about the air barrier. Think about how you’re going to integrate it into your process from the start and it’ll be much easier.” - Scott Stewart.
2. Failure to Integrate Airtightness Holistically: Another error is treating airtightness as an add-on rather than an integral part of the construction process. Simply adding an air barrier after the traditional construction methods are complete can lead to complications and inefficiencies. We’ve even heard stories of people hanging upside down during air barrier installation because of this issue! Instead, a holistic approach should be adopted from the outset which considers how to seamlessly integrate the air barrier into every stage of construction.
3. Underutilisation of Available Products: For instance, when retrofitting older buildings, many people forget about effective materials like lime render or other wet trades that can provide continuous air barriers. And with other innovative options becoming available, it’s important to know about and understand them as you can combine them on-site for optimal results.
4. Lack of Airtightness Testing at Various Stages: Failing to conduct airtightness testing at critical stages of construction is an oversight that can lead to unnecessary stress if you’re unable to pinpoint the source of air infiltration. Instead, testing should be done at multiple points, such as after the building wrap is installed, after windows are installed, and after trades have completed their envelope penetrations. Following this process will allow you to focus your time on where the leaks actually are, rather than trying to check every nook and cranny of the building.
How our Passivhaus Tradesperson course prepares you for managing airtightness on-site
Our Passivhaus Tradesperson course is designed to equip participants with the essential knowledge and skills to effectively manage airtightness on-site — alongside the other vital Passivhaus principles.
The course covers the fundamental concepts of airtightness, including air barrier continuity (ABC), moisture management, and the impact of air leakage on energy efficiency and building durability.
Participants gain a deep understanding of how airtightness contributes to the overall performance of Passivhaus buildings and practical strategies for dealing with air barrier penetrations and achieving airtightness using a combination of techniques and products.
Additionally, participants will have the chance to attend a hands-on Practical Training Day, covering installation techniques, tips and tricks on aspects like windows, ventilation, mechanical ventilation with heat recovery and more!
While much of the material comes from the original Passivhaus roots, our expert trainers, Scott and Madonna, have done an excellent job integrating the Australian context into the material to make it more applicable. They discuss local regulations, climate considerations and available products to help participants successfully apply Passivhaus in Australia.
“There are a lot of Passivhaus resources out there that focus on planning and design, but there isn’t as much on the construction and how to do it better. We want to bridge this knowledge gap through the trades course, and then sow the seeds for participants to continue growing this knowledge base throughout Australia.”
-Scott Stewart
Beyond the knowledge acquired through the course, our trainers encourage critical thinking, problem-solving and continuous learning post-course completion. Participants learn to evaluate and address potential challenges related to airtightness, enabling them to make informed decisions and adapt Passivhaus principles to real-world construction scenarios.
In summary, our Passivhaus Tradesperson course provides a comprehensive foundation in airtightness management, blending theoretical knowledge with practical skills tailored to the Australian context. Our participants graduate with the confidence and competence to implement airtightness strategies effectively (alongside other principles), contributing to the success and sustainability of Passivhaus projects in Australia.