Opening the loft/attic hatch in your bedroom during a heatwave is likely to warm up your room rather than cool it down. The temperature in the attic tends to be higher than the temperature inside your living spaces, especially during a heatwave.
When you open the loft/attic hatch, warm air from the attic will flow into your bedroom, causing the room temperature to increase. Attics typically have poor insulation and can become very hot, as they are exposed to direct sunlight and lack proper ventilation. Therefore, allowing the hot air from the attic to enter your living space will likely make your room even warmer.
To cool down your room during a heatwave, it's generally more effective to keep the loft/attic hatch closed and take other measures to minimize heat gain and promote ventilation. Here are some suggestions:
Use window coverings: Close curtains, blinds, or use reflective window films during the day to block out direct sunlight and prevent heat from entering your room.
Ventilate at the right time: Open windows during the cooler parts of the day, such as early morning and evening, to let in fresh air. You can also use fans or cross-ventilation to improve airflow.
Use fans or air conditioning: Place fans strategically to circulate air and create a cooling breeze. If available, use air conditioning units to lower the temperature.
Minimize heat sources: Turn off unnecessary electronics and lights that generate heat. Avoid using appliances that produce excess heat, such as ovens or dryers, during the hottest parts of the day.
Create a cooling environment: Use cool towels, ice packs, or a spray bottle with water to provide personal cooling when necessary. Wear lightweight and breathable clothing.
By implementing these measures, you can help maintain a more comfortable temperature in your room during a heatwave.