Heatwave: A simple trick that can lower your home’s temperature by up to 6°C
During a heatwave, many homes become unbearably hot because roofs, walls, and windows absorb sunlight throughout the day and release that heat indoors. One simple, low-cost technique that can significantly reduce indoor temperatures is using a “cool roof” method — covering or coating the roof with a reflective white layer.
The trick: Make your roof reflect sunlight
A large amount of heat enters a house through the roof. A dark roof absorbs solar radiation and can become extremely hot, sometimes reaching 60–80°C under strong sunlight. A white or reflective roof absorbs much less heat and reflects more sunlight back into the atmosphere.
Studies and practical experiences show that a reflective roof coating can reduce indoor temperatures by around 3–6°C in hot conditions, depending on the building design, climate, insulation, and ventilation.
How to do it
1. Paint the roof white
- Use white roof paint or a solar-reflective roof coating.
- White surfaces reflect a high percentage of sunlight.
- Apply two coats for better durability.
- Clean and dry the roof before painting.
2. Use a temporary low-cost method
If you cannot paint the roof:
- Place a white sheet, reflective tarp, or light-colored fabric above the roof (leaving an air gap).
- Use bamboo mats or shade structures to block direct sunlight.
- Keep the covering slightly above the roof so hot air can escape.
3. Add roof insulation
A reflective roof works even better when combined with insulation:
- Foam boards
- Mineral wool
- Reflective foil sheets
- Ceiling insulation materials
Insulation slows heat transfer from the roof into rooms.
Other simple ways to cool your home during a heatwave
1. Block sunlight during the hottest hours
- Close curtains, blinds, or shutters on sunny windows.
- Use light-colored curtains because they reflect heat.
- External shading (awnings, trees, shades) works better than indoor curtains.
2. Ventilate at the right time
- Open windows during cooler hours (early morning and night).
- Close windows when outdoor air becomes hotter than indoor air.
3. Create cross-ventilation
Open windows or doors on opposite sides of the house to allow airflow.
4. Reduce indoor heat sources
- Turn off unused lights.
- Avoid using ovens and stoves during peak heat.
- Use LED bulbs instead of incandescent bulbs.
5. Use the “night cooling” method
At night:
- Open windows to release stored heat.
- Use fans to move cool air inside.
- Close windows and curtains again before the outdoor temperature rises.
Why the 6°C reduction happens
The effect comes from three main changes:
- Less solar absorption
A reflective roof receives less heat from sunlight. - Lower roof surface temperature
The ceiling below the roof stays cooler. - Reduced heat radiation indoors
Walls and furniture absorb less heat during the day.
Important note
A 6°C drop is not guaranteed in every home. It depends on:
- Roof material and color
- Amount of sunlight
- House insulation
- Number and size of windows
- Local climate
However, a reflective roof combined with shading and good ventilation is one of the cheapest and most effective passive cooling methods for hot climates.