THE INDOOR CLIMATE BRIEFING

Take a deep breath

Within 10 seconds of being born, we take a breath of air. Then we continue for the rest of our lives, 15 breaths a minute, 11,000 litres a day¹.

This highlights the vast amount of air that passes through our bodies in a lifetime. Considering that "the rest of our lives" is spent 90 percent indoors², the quality of indoor air becomes profoundly important. While all air contains pollutants to varying degrees, indoor air can be up to five times more polluted than outdoor air³. Significant efforts are made to reduce outdoor air pollution, but less focus is often placed on indoor air quality.

This briefing addresses key questions: How can we determine if the air we breathe is good or bad? What are the health risks associated with poor indoor air quality, and how is healthy air defined? How do sustainable buildings contribute to better indoor environments, and vice versa?

To answer these questions, insights from a wide range of sources have been gathered and compiled into this clear, educational, and accessible document, designed to shed light on the invisible air around us and its significance.

15 breaths a minute

11,000 litres a day

Key insights

How is the air we breathe in Europe?

While research comparing indoor air quality across Europe is limited, outdoor air quality is better documented, directly affecting indoor air. A steady inflow of outdoor air is needed to replace stale indoor air, which tends to accumulate pollutants and reduce comfort. The challenge arises when outdoor air itself is polluted.

Air enters buildings through three primary methods: infiltration (cracks and gaps), natural ventilation (open windows/doors), or mechanical ventilation (controlled systems). Insulation and ventilation methods are crucial. Higher rates of outdoor air replacement reduce pollutant risks, with infiltration having the lowest air exchange rate and mechanical ventilation the highest, often incorporating filters.

Air quality, insulation, and ventilation collectively influence indoor air and reveal regional differences. This document focuses on four regions: North, West, South, and East, comparing air quality based on annual PM2.5 (dust particles) levels, as these show stronger and more consistent health effects.

Insulation & ventilation

Northern European homes are typically well-insulated with airtight construction and triple-glazed windows, necessitating mechanical ventilation for air quality. Western Europe generally has good insulation, particularly Germany and the Netherlands, though older homes may rely on passive ventilation.

Southern Europe traditionally has poorer insulation due to the warm climate, with natural ventilation being common, though mechanical systems are increasing in newer buildings. Eastern Europe presents a mixed picture: newer buildings have better insulation, but older ones often lack adequate ventilation, leading to moisture and mold issues.

EU wants to raise the standards

Regions with the poorest outdoor air quality often have the lowest access to mechanical ventilation. Colder climates typically encourage better insulation, which in turn demands more effective ventilation. EU directives, like the Energy Performance of Buildings Directive, are driving improvements in building insulation and mechanical ventilation to enhance energy efficiency and indoor air quality across all regions.

Healthy air indicator

A thermometer graphic illustrates air quality levels:

• EXCELLENT
• GOOD
• FAIR
• POOR
• BAD

The thermometer is an illustration based on WHO recommendations for healthy air (max 5 µg/m³ PM2.5 annually) and EEA measurements.

Northern Europe: Sweden, Norway, Finland, Denmark, Iceland, Estonia, Latvia, Lithuania

Western Europe: Germany, France, Netherlands, Belgium, Austria, United Kingdom, Ireland, Luxembourg

Southern Europe: Italy, Spain, Portugal, Greece, Cyprus, Malta

Eastern Europe: Poland, Czech Republic, Slovakia, Hungary, Romania, Bulgaria, Serbia, Bosnia and Herzegovina, North Macedonia, Croatia, Slovenia, Albania, Kosovo, Montenegro

Factors for healthy indoor air

This briefing focuses on the common international factors defining indoor air quality:

1. Carbon dioxide
2. Relative humidity
3. Temperature
4. Particulate matter
5. Volatile organic compounds

Digitisation and sensor technology enable continuous real-time monitoring of these factors, often integrated into building management systems or dedicated indoor air quality monitors. In essence, these technologies allow us to visualise the invisible.

1. How does carbon dioxide affect us?

Carbon dioxide (CO2) is a naturally occurring, odorless gas. We exhale it, but it also originates from sources like space heaters, clothes dryers, and stoves. Indoor concentrations are often higher, directly correlating with the number of occupants. High CO2 levels can indicate stale air, which typically contains more particles and pollutants¹⁶.

How you notice

Elevated CO2 levels can cause symptoms such as headaches, drowsiness, difficulty concentrating, and reduced productivity¹⁶.

What to aim for

An ideal CO2 concentration is generally considered to be between 400-800 parts per million (ppm). Well-ventilated buildings typically maintain levels around 600-800 ppm, while outdoor levels are around 350-450 ppm¹⁷.

What you can do

The most effective way to reduce CO2 is to increase airflow by enhancing ventilation. If this is not feasible, opening doors or windows is a simple solution, assuming the outdoor air is clean.

2. Relative humidity - an absolute health factor

Relative humidity (RH) measures the amount of moisture in the air relative to the maximum it can hold at a given temperature. Warm air holds more moisture than cold air; thus, as temperature rises, RH drops, and vice versa. Low humidity is common in winter when heated indoor air becomes dry.

How you notice

Low humidity can irritate mucous membranes, increasing susceptibility to cold viruses. It can also cause nosebleeds, dry eyes, dry skin, and sinus discomfort. High humidity promotes the growth of molds and other biological contaminants, leading to symptoms like sneezing, runny nose, red eyes, skin rashes, and triggering asthma attacks^{23, 24}.

What to aim for

Research suggests that a healthy RH level for both people and buildings is between 40-60 percent, minimizing mold growth, irritation, and virus transmission²⁵.

What you can do

To combat dry air, slightly lowering the temperature can help. For high humidity, increasing ventilation is recommended. Dehumidifiers are useful for specific situations like water damage or precise humidity control. Persistent high humidity may indicate issues with pipes or plumbing leaks.

3. Temperature - cold facts on a hot topic

Temperature is often the primary consideration in discussions about indoor air, being the most noticeable and adjustable factor. The goal is thermal comfort, defined as "that condition of mind that expresses satisfaction with the thermal environment"¹⁸. Perceived comfort varies with age, clothing, health, and personal preference. While temperature is central, thermal comfort also depends on radiant temperature, air movement, humidity, clothing, and activity level.

How you notice

High temperatures can lead to fatigue and difficulty concentrating, potentially exacerbating existing pollution. Low temperatures can hinder physical activity. Both extremes can affect mental acuity, work capacity, strength, and mobility¹⁹.

What to aim for

Generally, a suitable indoor temperature is 23-26°C in summer and 20-24°C in winter^{20, 21}. Summer temperatures may need to be warmer to compensate for light clothing and the difference from outdoor temperatures. A cooler room (16-20°C) is recommended for sleep, as body temperature naturally drops during rest²².

What you can do

Individuals often know their preferred temperature. For larger spaces with multiple occupants, tools like Predicted Mean Vote (PMV), Percentage of Dissatisfied (PPD), and Draught Rate can help designers create environments that feel comfortable for most people, considering thermal conditions and airflow.

4. Why particulate matter, matters

Particulate matter (PM) consists of dust particles floating in the air, originating from natural sources like sandstorms and forest fires, as well as human activities such as fossil fuel combustion, fireworks, and tobacco smoke. PM is categorized by size, with PM10 being smaller than 10 micrometers.

How you notice

Most particulate matter lodges in the lungs, but smaller particles can enter the bloodstream and spread to other organs. High levels can cause short-term health effects including irritation of the eyes, nose, throat, and lungs, as well as coughing, sneezing, runny nose, and shortness of breath²⁶.

What to aim for

WHO guidelines recommend an annual average of 5 micrograms of PM2.5 per cubic meter of air or less⁶. This can be monitored using indoor air sensors.

What you can do

Prioritize keeping premises clean and dust-free. Ensure ventilation systems have good quality HEPA filters to remove outdoor particles. For existing indoor particles, consider using an air purifier with HEPA filters.

5. The thousand gases of our everyday lives

Volatile organic compounds (VOCs) are a collective term for thousands of different gases used and produced in daily life. Indoor concentrations can be up to ten times higher than outdoors²⁷. VOCs are found in cleaning products, perfumes, and are generated by activities like cooking and smoking, as well as from furniture and building materials.

How you notice

Short-term effects may include headaches, nausea, cough, dizziness, and irritation of the nose, throat, and skin. Long-term effects can manifest as seemingly normal symptoms, such as allergic skin reactions or leg cramps²⁸.

What to aim for

An ideal VOC concentration is 300 micrograms per cubic meter of air or less. Levels between 300 and 500 µg/m³ are considered acceptable, with higher levels potentially causing irritation and discomfort²⁹.

What you can do

Reduce the number of products that emit VOCs by checking labels for low-emission options. Increase ventilation when using products that emit VOCs. If no ventilation system is available, opening doors and windows can temporarily help remove stale air and introduce fresh outdoor air.

Good air do us good

Creating environments with healthy indoor air promotes activity, happiness, and high functioning. It's not only about reducing negative health effects but also about enhancing positive ones, often going hand-in-hand.

Sustainable buildings and energy-efficiency

Sustainable buildings are designed for long-term durability and comfort with minimal environmental impact. In Europe, these buildings are guided by the Energy Performance of Buildings Directive, which sets Minimum Energy Performance Standards and supports the EU Green Deal's goal of a climate-neutral building stock by 2050.

Final thoughts

Outdoor air quality and pollution are significant concerns for the public and governing bodies. Indoor air, however, is often overlooked despite the substantial time spent indoors. Considering this, indoor air deserves at least as much attention as outdoor air, particularly from a health perspective.

The EU has introduced directives and goals to accelerate the renovation of sustainable, energy-efficient buildings. While driven by climate impact and cost reduction, these renovations also impose higher requirements on ventilation and other elements that improve indoor air quality, yielding significant health benefits.

Current building techniques and ventilation practices across Europe show considerable differences, influenced by climate and past knowledge gaps regarding indoor air's impact on health. EU directives help streamline construction and ventilation, improving indoor air quality. However, responsibility extends beyond governments; individuals can and should demand better air quality in all environments.

We can all demand better air quality in our gyms, schools, hotels - and above all, in our homes. After all, our health is at stake if the indoor air is poor.

Most of us spend the majority of our time indoors. Indoor climate is crucial to how we feel, how productive we are and if we stay healthy.

We at Lindab have therefore made it our most important objective to contribute to an indoor climate that improves people's lives. We do this by developing energy-efficient ventilation solutions and durable building products. We also aim to contribute to a better climate for our planet by working in a way that is sustainable for both people and the environment.

Lindab | For a better climate