German experts advise partially open roller shutters to prevent summer heat buildup

Closing roller shutters completely during hot weather can create a sealed space between the shutter and the window. Sunlight heats this cavity, and without fresh air the temperature can rise sharply, leading to uncomfortable indoor heat and even risk of glass breakage or shutter deformation.

To avoid these problems, experts recommend leaving a ventilation gap of about 5–10 cm at the bottom of the shutters. This allows air to circulate, prevents heat stasis, and still provides shade. The shutters should be drawn down to block direct sun, but the small opening ensures that light can enter and that indoor CO₂ and humidity can be released through brief, regular ventilation—ideally in the cooler evening or early‑morning hours.