{"id":997617,"date":"2026-09-22T08:00:00","date_gmt":"2026-09-22T06:00:00","guid":{"rendered":"https:\/\/kienzler-klima.de\/?p=997617"},"modified":"2026-08-19T11:26:12","modified_gmt":"2026-08-19T09:26:12","slug":"role-of-airtightness-in-building-indoor-climate","status":"publish","type":"post","link":"https:\/\/kienzler-klima.de\/en\/role-of-airtightness-in-building-indoor-climate\/","title":{"rendered":"What role does airtightness of a building play in indoor climate?"},"content":{"rendered":"
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The airtightness of a building directly and significantly influences the indoor climate: a well-sealed building loses less energy through uncontrolled leakage and maintains temperature and humidity more stably. At the same time, high building airtightness prevents natural air exchange, meaning indoor air quality quickly deteriorates without a deliberate ventilation strategy. The following sections explore how airtightness and indoor climate are connected, what risks overly tight buildings present, and which ventilation solutions provide the right balance.<\/p>\n

How does airtightness affect indoor air quality?<\/h2>\n

High building airtightness reduces uncontrolled air exchange through cracks, joints, and leaky connections. This improves energy efficiency, but also means that pollutants, CO\u2082, and moisture generated indoors can no longer escape naturally. Indoor air quality in an airtight building therefore depends entirely on controlled ventilation.<\/p>\n

In conventional, less airtight buildings, so-called infiltration ventilation \u2014 the diffuse entry of air through building component joints \u2014 provided a certain baseline exchange. Modern buildings built to current energy standards seal these joints consistently. This makes sense from an energy perspective, but fundamentally changes the conditions for indoor air quality. Anyone planning or renovating a house today must treat ventilation and building airtightness as an inseparable pair.<\/p>\n

This is particularly relevant in practice for pollutants from building materials, cleaning products, and furnishings, as well as for the rise in CO\u2082 from breathing. Even with just a few people in a well-sealed room without ventilation, CO\u2082 levels rise within a short time to values that noticeably impair concentration and well-being.<\/p>\n

What happens to indoor air when a building is too airtight?<\/h2>\n

If a building is very airtight without controlled ventilation in place, pollutants, moisture, and CO\u2082 accumulate in the indoor air. The consequences range from increased risk of mold and odor problems to health complaints such as headaches, fatigue, and difficulty concentrating.<\/p>\n

Moisture loading is particularly critical. People release significant amounts of water vapor through breathing and perspiration alone, with additional contributions from cooking, showering, and plants. In a tight building without adequate ventilation, this moisture condenses on cooler building surfaces, promoting mold growth. Mold is not just an aesthetic problem but a serious health risk, especially for people with respiratory conditions.<\/p>\n

In addition, volatile organic compounds (VOCs) from paints, adhesives, and plastics can accumulate in indoor air when no air exchange takes place. Building airtightness therefore only truly provides protection when combined with a well-thought-out ventilation strategy.<\/p>\n

What role does the ventilation system play in an airtight building?<\/h2>\n

In an airtight building, the ventilation system takes over entirely the task the building itself can no longer perform: the controlled exchange of stale indoor air for fresh outdoor air. It is therefore not an optional add-on, but a technical necessity to ensure air quality, moisture balance, and health protection.<\/p>\n

Modern ventilation systems with heat recovery are particularly efficient: they extract up to 90 percent of the heat contained in the exhaust air and transfer it to the incoming fresh air. This allows the energy efficiency of airtightness to be fully exploited without compromising air quality. Building ventilation and building airtightness thus form a system that must be considered together during planning.<\/p>\n

For the distribution of supply air throughout individual rooms, choosing the right air distribution system is crucial. Conventional sheet metal duct systems and textile ventilation systems<\/a> differ in several relevant respects, which will be explored in the next section.<\/p>\n

How do textile and conventional air distribution systems differ in airtight buildings?<\/h2>\n

The key difference lies in the way air is discharged: conventional sheet metal ducts direct air to defined outlets where it exits at higher velocity. Textile air distribution systems, by contrast, release air evenly across the entire permeable surface of the duct, with very low discharge velocity and no drafts.<\/p>\n

Uniform air distribution without drafts<\/h3>\n

In airtight buildings where the ventilation system is the sole source of fresh air, the quality of air distribution is of particular importance. Textile air ducts distribute supply air along their entire length, reliably preventing temperature stratification and localized drafts. The indoor climate therefore remains consistently homogeneous, regardless of whether the system is operating in heating or cooling mode.<\/p>\n

Installation and material costs compared<\/h3>\n

Another practical advantage concerns the installation effort. Textile air distribution systems can be installed significantly faster than sheet metal duct systems and enable savings of up to 60 percent in material and installation costs. This is a considerable advantage especially for retrofits in existing buildings, where space constraints and installation accessibility are often challenging. More about the possible applications across various industries and applications<\/a> is provided in the corresponding overview.<\/p>\n

When does it make sense to retrofit ventilation in existing buildings?<\/h2>\n

Retrofitting ventilation in existing buildings makes sense when building airtightness has been increased through energy-efficient renovation, when mold problems occur repeatedly, or when indoor air quality is noticeably impaired. Increased requirements for hygiene or energy efficiency can also provide the impetus.<\/p>\n

Typical triggers for a retrofit include:<\/p>\n