In Switzerland, good thermal insulation of buildings is not only a question of energy efficiency, but also a legal requirement and increasingly an ecological statement. The choice of insulation materials and their optimum thickness influence energy consumption and therefore also the environmental balance and investment costs. In this article, we examine the ideal insulation thicknesses for common materials and relate these to legal requirements, Minergie standards and ecological and economic criteria.

Legal requirements: Focus on the U-value
The cantonal energy ordinances (MuKEn 2014) require certain heat transfer coefficients (U-values) for new buildings and renovations. This value indicates how much heat is lost per square metre and one degree of temperature difference per hour through a building component - the lower the value, the better the insulation.
A maximum U-value of 0.17-0.25 W/m²K generally applies to external walls.

Minergie standards
If you want more, go for Minergie. The voluntary Minergie standards go beyond the minimum legal requirements. The target U-value for external walls is typically 0.15 W/m²K or even better. To achieve this, thicker or more efficient insulation materials are required - an investment that pays off in the long term.

Ideal insulation thicknesses according to material
1.glass wool
- Lambda value: approx. 0.035 W/mK
- Thickness: 16-22 cm (legal) / 24-30 cm (Minergie)
- Advantages: Inexpensive, flame retardant, good availability
- Ecology: Energy-intensive production, recyclable

2. rock wool
- Lambda value: approx. 0.035-0.040 W/mK
- Thickness: 18-24 cm (legal) / 26-32 cm (Minergie)
- Advantages: Fire protection, sound insulation, durable
- Ecology: Similar to glass wool, robust, recyclable

3. cellulose (blown-in insulation)
- Lambda value: approx. 0.040-0.045 W/mK
- Thickness: 20-26 cm (legal) / 28-34 cm (Minergie)
- Advantages: Good eco-balance, CO₂-binding
- Ecology: Made from recycled paper, very sustainable

4. soft wood fibre
- Lambda value: approx. 0.038-0.045 W/mK
- Thickness: 20-26 cm (legal) / 28-36 cm (Minergie)
- Advantages: Open to diffusion, good summer heat storage
- Ecology: Natural, regionally available, sustainable

Conclusion: Holistic planning pays off
The ideal insulation thickness depends heavily on the material used, the desired energy standard (e.g. Minergie) and the legal requirements. While mineral insulation materials such as glass wool and rock wool score highly in terms of price and fire protection, ecological alternatives such as cellulose and soft wood fibre impress with their sustainability and healthy living.

From an economic point of view, investing in more insulation is worthwhile in many cases - especially with rising energy prices and subsidy programmes. The decisive factor is a holistic view of ecology, economy and legal compliance.