airtightness in the construction

In modern construction technology, the airtightness of buildings plays a crucial role. But what does airtightness actually mean? Airtightness refers to a building’s ability to prevent uncontrolled air flow through leaks. Today, the airtightness of a building is a key quality feature for energy-efficient and damage-free construction. It influences energy consumption, indoor climate, building fabric, and living comfort. It is therefore crucial for craftsmen, architects, and specialist planners to understand the principles of airtight construction—and to implement them correctly. Here you will find the most important information on the subject of airtightness in construction and what mechanical ventilation systems actually have to do with it.

 

 

The importance of airtightness in buildings

Airtightness plays a crucial role in construction and building technology, as it contributes significantly to energy efficiency and indoor climate. An airtight building protects against uncontrolled air exchange. By specifically controlling air permeability, heating costs can be reduced and mold growth prevented.

 

Air tightness ensures that no uncontrolled air flows escape or enter through the building envelope. The advantages:

• Energy efficiency: Uncontrolled air exchange increases heating and cooling requirements.
• Protection of the building fabric: Prevents moisture ingress and condensation in the structure.
• Indoor climate: Consistent temperatures, no drafts, better sound insulation.
• Health & hygiene: Air quality can only be ensured with controlled ventilation.

The airtightness of a building is influenced by various factors, including the quality of construction, the choice of building materials, and the sealing of component connections. Leaks in the building envelope can lead to unwanted heat loss and impair the comfort of the rooms. More heating or cooling is required to maintain a comfortable indoor climate, which in turn can lead to higher energy costs and an unnecessary loss of resources.

 

Windows, doors, and critical connections

Air-tight building envelopes require careful execution, especially in the case of:

• Window connections (air-tight on the inside, diffusion-open on the outside)
• Roof penetrations
• Installation penetrations

However, the airtight design of modern new buildings in particular prevents the natural exchange of air through joints and gaps, which in older buildings (albeit unintentionally) ensured continuous ventilation. This “problem” does not usually arise in modern new buildings, but it does pose another challenge: airtight construction generally requires mechanical ventilation – otherwise there is a risk of moisture damage and poor air quality.

 

 

Standards, requirements, planning

Relevant regulations:

• DIN 4108-7: Planning & execution of airtight layers
• DIN EN ISO 9972: Measurement of airtightness
• GEG: Legal requirements for energy efficiency
• DIN 1946-6: Ventilation concept – legally required for new buildings

Important: According to DIN 1946-6, every airtight construction must be checked to ensure that sufficient ventilation can be provided without mechanical systems. In practice, this is almost never the case – therefore, mechanical ventilation is not optional, but essential.

 

Planning & implementation in practice

Air tightness is a planning task, not a “construction task,” therefore:

• Clearly indicate the air tightness level in the plan (e.g., color code in sections)
• No system breaks between trades
• Specify and coordinate airtight materials at an early stage

Tips:

• Pay attention to details and tested systems in the tender
• Communication across trades (e.g., roofers – drywallers – electricians)

Component connections: Windows, doors & details

The component connections of windows, doors, and other details are crucial for the airtightness of a building. Careful execution of these connections is essential to prevent uncontrolled air currents and thus ensure energy efficiency.

 

Even the best insulation values are useless if windows and doors are not installed properly to be airtight. Typical weak points:

• Window connections: must be airtight on the inside and wind and driving rain tight on the outside. For windows, the connection to the surrounding area is particularly important. Leaks can occur here, which impair the overall thermal insulation. Special sealing systems and installation techniques are necessary to create an airtight connection between the frame and the masonry.
• Roof connections: Eaves, valleys, and roof penetrations are complex and require special care.
• Installation penetrations: Cables, ventilation pipes, or sockets in exterior walls require special collars or sealing tapes. Yes, even small details play an important role. Connections of cables, pipes, and electrical penetrations must be carefully sealed. Any leaks can lead to unwanted heat loss and impair energy efficiency. Special materials such as sealing tapes, sealants, and films are used to ensure the airtightness of component connections. These materials must be processed professionally in order to be fully effective.

Careful planning and execution of component connections can prevent unwanted air currents and ensure the quality of the building envelope.

 

Planning and implementation

Air-tight construction does not begin on the construction site, but rather in the planning stage. Air-tight sealing layers must be planned and consistently represented in the design phase.

Materials:

• Vapor barriers and air-tight sealing membranes (e.g., for roofs and walls)
• Adhesive tapes, butyl rubber, sealants
• Cuffs for pipe penetrations

Construction site practice:

• Clearly define execution details
• Regular construction site inspections
• Air tightness test before interior work if possible

Common mistakes & how to avoid them

Many leaks are caused by minor oversights:

• Incomplete bonding or loose sealing membranes
• Subsequent penetrations without reworking
• Use of unsuitable materials (e.g., adhesive tapes that come loose in cold weather)

Recommendation:

• Use checklists
• Offer training for trades
• Clearly define responsibilities

Further questions

What is the difference between airtight and windproof? Airtight means that no air can flow through the building envelope (inside). Windproof means protection from external wind influences.

Is a house too airtight? No – if there is a functioning ventilation concept. Without airtightness, structural damage occurs – not because of “too little air.”

Does every building need an airtightness test? For subsidized construction projects and passive houses, yes – but in any case, it is highly recommended for quality assurance.

 

Measuring airtightness: Blower door test & n50 value

A common method for measuring airtightness is the blower door test. In this test, a fan is installed in a door or window of the building. The fan creates positive or negative pressure in the building, which reveals any leaks in the building envelope.

 

Key indicator:

The n50 value – this shows how often the air volume per hour is exchanged at 50 pascals due to leaks.

 

Limit values depending on building standard:

≤ 3.0 1/h – conventional buildings

≤ 1.5 1/h – energy-efficient houses

≤ 0.6 1/h – passive houses

The lower the n50 value, the more airtight the building – and the more urgent the need for mechanical ventilation

 

Performing a blower door test is an important step in the construction process to ensure that the airtightness of a building meets the required standards. Decentralized ventilation systems can help to create an optimal indoor climate without compromising airtightness.

Airtightness & mechanical ventilation: two sides of the same coin

 

Modern buildings are now so airtight that natural air exchange practically no longer takes place. However, the people living in them produce moisture, CO₂, and odors—which have to escape somehow.

Why mechanical ventilation is often mandatory in new buildings:

• Air can no longer circulate “just like that”—there are no gaps or leaks.
• Moisture from the kitchen, bathroom, washing, and breathing must be removed.
• Pollutants (VOC, formaldehyde, CO₂) from furniture, building materials, or occupants accumulate.
• Window ventilation is unreliable and inefficient—especially when no one is home.

Solution: Controlled residential ventilation (CRV)—centralized or decentralized

 

• Central systems: Ideal for new buildings with a continuous planning concept.
• Decentralized ventilation systems: Also suitable for new buildings and the individual ventilation of individual rooms (e.g., bedrooms, bathrooms), but are also ideal for renovations, as unlike central solutions, they do not require complex duct systems.

With heat recovery, up to 90% of the exhaust air heat can be used – this not only ensures fresh air, but also reduces heating costs.

 

Decentralized ventilation as a solution:

Thanks to their efficient operation, decentralized ventilation systems help to supply fresh air in a targeted manner and remove stale air without affecting the building envelope. They enable individual rooms to be ventilated according to their specific needs, which is particularly important in times of high energy standards and building physics requirements.

 

Compared to central ventilation systems, decentralized ventilation systems score points for their flexibility and adaptability to different building structures. They offer the possibility of responding specifically to the individual needs and requirements of a building. Thanks to their modular design, they can be easily integrated into existing or new buildings without requiring major renovation work.

 

Another advantage of decentralized ventilation systems is their energy efficiency. Thanks to modern technologies such as heat recovery, they help to reduce energy consumption and thus save costs. These systems enable controlled air circulation while maintaining a high level of airtightness, which has a positive effect on the indoor climate and living comfort.

 

The simple installation and maintenance of decentralized ventilation systems make them an attractive solution for builders, architects, and planners. They offer the possibility of effectively regulating the indoor climate in buildings while ensuring airtightness. With their demand-based control, they contribute to the optimization of energy consumption and thus make an important contribution to sustainability in construction.

 

Further interesting articles

When maintaining a ventilation system, certain aspects are crucial for efficiency and longevity. Learn more about the most important points for maintenance in this article on our website. We also provide an overview of the ASR A3.6 requirements for ventilation in operation here.

Energy-efficient living through the use of ventilation systems and heat pumps is an important step toward reducing energy consumption. Find out what options are available for heating and ventilating your home efficiently in our article here. 

Retrofitting ventilation technology is becoming increasingly important, not only in new buildings, but also in the course of energy-efficient renovation of existing buildings. Decentralized ventilation units in alternating mode of operation are being used more and more due to their ease of integration. Research into user-oriented control of residential ventilation systems has produced innovative control strategies. You can find more information about these strategies in this report.

 

Air tightness is a decisive factor for energy efficiency and well-being in buildings. Innovative ventilation systems such as decentralized ventilation can achieve optimal air exchange while reducing energy costs. Measurements such as the blower door test and the n50 value help to check air tightness. With a focus on component connections and compliance with relevant standards and regulations, buildings can be designed to be airtight and energy-efficient. Decentralized ventilation systems usually offer compelling and sensible additions for an optimal indoor climate. We would be happy to inform you about suitable ventilation options for your construction project. Just get in touch with us.