The breathing façade

The scene shows a façade section layer by layer: the outer cladding (ceramic, stone, timber, fibre cement, aluminium, HPL…), the ventilated air cavity, the insulation and the backing leaf. The arrows and colour gradient show the air moving through the cavity: it enters at the bottom, heats up on contact with the sun-warmed cladding, and exits at the top. The better that cavity "draws", the more heat gets removed before it reaches the insulation.

• Transmittance (U)

  The insulation of the whole assembly in W/m²·K. The lower it is, the less heat passes through.

• Cladding temperature

  How hot the outer skin gets in the sun. In a ventilated cavity, much of that heat leaves with the air rather than moving inward.

• Cavity temperature

  The air inside the cavity. The difference with the outdoor temperature is what drives the chimney effect.

• Airflow rate and speed

  How much air circulates through the cavity (m³/h per metre of façade). Depends on cavity width, openings and thermal draw.

• Heat removed by ventilation

  The W/m² the cavity carries away before it reaches the interior: the real benefit of ventilating.

• Thermal load reduction

  How much the load reaching the interior drops compared with a façade with no cavity, in %.

• Condensation risk

  Compares the cavity's humidity with its dew point. Ventilation also dries: it prevents mould and degradation.

The header buttons load real-world situations: a summer day in Córdoba (38 °C and blazing sun), a winter in Galicia (cold, damp and windy), a summer night, and two key comparisons — a well-designed cavity versus a narrow cavity or a blocked outlet— to see how a poorly resolved construction detail cancels out the chimney effect. You can also change the cladding, insulation and backing-leaf material to compare.