How to Keep a House That Gets Too Hot Cooler

A house that gets too hot during the day does not retain heat simply because the outside air is warm. Its roof, walls and windows are exposed to solar radiation for hours, absorbing some of that energy before passing it indoors. That is why certain rooms can still feel stuffy long after sunset. The most effective way to lower the temperature is to stop heat getting in and ventilate only when the outdoor air is cooler.

Why does the house stay warm after the sun has gone down?

Concrete, brickwork, roof tiles and similar materials take in energy while they are in the sun. This thermal load does not vanish as soon as night falls: walls and roof slabs gradually release their stored heat, keeping indoor spaces warm for several hours.

The issue is often more pronounced in top-floor rooms and along walls exposed to the strongest afternoon sun. Pay particular attention to:

• Roofs and roof slabs in direct sunlight;
• Walls exposed to sunshine for long periods;
• Windows without blinds, curtains or external shading;
• Rooms with limited air circulation;
• Dark external surfaces, which absorb more radiation.

When is the best time to open the windows?

Opening every window during the hottest part of the day can have the opposite effect, letting even warmer air inside. Instead, keep windows and sunshades closed while the outdoor temperature is higher, then create cross-ventilation early in the morning, at night, or whenever the air outside is cooler than indoors.

How can you stop the sun heating walls and windows during the day?

Preventing solar radiation from reaching a surface is generally more effective than trying to remove the heat afterwards. Awnings, trees, pergolas, shutters and other types of external shading directly reduce the energy reaching windows and walls.

Internal curtains and blinds can help too, especially when they are closed before sunlight reaches the room. On the outside of the building, lighter colours generally reflect a greater proportion of radiation than very dark surfaces.

• Close blinds before direct sunlight reaches the window;
• Use awnings or other external shading where possible;
• Provide shade for walls that receive strong afternoon sun;
• Consider light shades for façades that become very hot;
• Do not leave dark furniture in direct sunlight through glazing.

Why should the roof be considered before buying another fan?

The roof is often among the surfaces receiving the most solar radiation throughout the day. Thermal insulation, a reflective roof covering suited to the building system, and effective waterproofing can all reduce the heat transferred to the rooms below. A fan improves how cool the air feels on the skin, but it cannot stop a heated roof slab from radiating warmth indoors.

Lowering the temperature starts by keeping heat out

Air conditioning can remove heat from a room, but it has to work harder while walls, ceilings and furniture are still releasing stored energy. Before increasing the unit’s capacity, passive measures such as shading, insulation, ventilation at the right times and window protection can reduce the thermal load that needs to be managed.

A cooler house, then, relies less on one single solution and more on identifying where the heat is entering. If it comes through the roof, insulation may have the greatest impact; if it mainly affects one particular room in the afternoon, shading and window protection may eliminate much of the discomfort. The principle is straightforward: the less solar radiation a building absorbs during the day, the less heat it will return to its occupants at night.