The most effective way to cool a 1930s Dutch house without AC is to block sunlight before it enters, create strong cross-ventilation at night, and use fans strategically to move air. Start by closing curtains or blinds on the west-facing side before 18:00 to stop the sun from heating your home, then open windows on opposite sides after sunset to flush out hot air.

For your specific situation where the sun hits after 18:00, invest in blackout curtains or reflective window film. These are temporary, HOA-friendly solutions that block solar radiation. During the day, keep windows closed and curtains drawn on the sunny side. Open windows only on the shaded side if you need airflow, but avoid letting direct sun in. At night, when outside temperature drops below indoor temperature (usually after 22:00), open windows wide on both sides of your home to create cross-ventilation. Place a fan in one window blowing inward and another in a different window blowing outward to maximize air exchange.

Another trick is to use a bowl of ice water in front of a fan. The fan will blow cooler air across the ice, lowering the room temperature by a few degrees. You can also wet a thin sheet or towel and hang it in front of an open window with a fan behind it. Evaporative cooling works well in dry heat, but be aware that in humid conditions it may feel less effective.

Reduce indoor heat sources: avoid using the oven, stove, or dryer during the day. Cook outside on a barbecue or eat cold meals. Turn off electronics when not in use, as they generate heat. If you have a basement, spend time there during the hottest hours. For sleeping, consider a cooling mattress pad or a damp cloth on your forehead.

Tradeoffs: These methods require active management and won't cool your home as much as AC. Blackout curtains may make rooms dark during the day. Evaporative cooling adds humidity, which might be uncomfortable if you're already sweaty. But they are cheap, temporary, and HOA-friendly.

Next steps: Measure your indoor temperature at different times to see which windows are most effective. Experiment with fan placement. If you own the home, consider installing external sun blinds (zonwering) on the west side, which are often HOA-approved and more effective than internal curtains. Check with your HOA about temporary window film or external shades before buying.

By combining these strategies, you can lower your indoor temperature by 3-5 degrees Celsius without AC, making the heatwave much more bearable.