Daniela Matsuzaki

September 22, 2026, 4:42 am | Read time: 4 minutes

How heat buildup occurs in rooms

It’s a familiar summer scenario: you can still breathe easily in the bedroom, while the air in the adjacent living room is stifling. We often blame the sun for this, but that’s only part of the story. How much a room heats up in summer and how long it retains the heat depends not only on the room’s orientation and size. Building physics factors such as the mass of the exterior walls, the type of glazing, and even the ceiling height can play a crucial role.

The orientation of the house plays a crucial role

The direction the house faces is often decisive and significantly contributes to how much solar energy a room can absorb. The sun moves from east to west via the south during the day. While south-facing rooms receive the most intense sunlight, west-facing rooms are particularly prone to extreme heat buildup. The afternoon sun hits already warmed exterior air. This energy transfers to furniture and walls and is perceived as stagnant heat well into the night. In contrast, rooms on the north and east sides remain cooler, even if they are the same size.

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Are window surfaces partly responsible for heating up rooms?

Windows can often act like greenhouses for rooms, as they allow shortwave solar radiation to enter unimpeded. This creates longwave heat energy that cannot easily escape through the window. In summer, this can quickly lead to overheating, especially in rooms without external shading. This effect is further intensified when regular window glass is used.

Which windows generate more heat in the room?

Not only shading but also the proper window equipment helps effectively prevent rooms from heating up in summer. Windows with solar control glass, meaning with a low g-value, can act like a shield. Windows with a high g-value of over 60 percent allow sunlight to enter the room unimpeded. Particularly old windows with single glazing and old double-glazed windows without thermal protection coating are especially vulnerable.

More on the topic

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In the Summer 4 Mistakes That Turn Your Apartment Into a Heat Trap

Do rooms with exterior walls heat up faster?

Exterior walls can absorb heat from sunlight and air, which is then released into the interior with a delay. This often happens in the evening or at night. Additionally, a dark facade color, a southwestern orientation, and large windows without external shutters can amplify the effect. Poor insulation of exterior walls can also cause heat to enter the house more quickly. If you want to keep it cooler in summer, you should definitely consider these factors.

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Do floors and ceiling height affect how rooms warm up in summer?

Ceiling heights play a certain role in summer warming. This is related to the available air volume. The more volume there is, the longer it takes to warm up. Additionally, warm air rises, so the lower living area remains cooler. However, there is no “best” ceiling height that could completely prevent warming.

Floors, on the other hand, can also influence the room temperature. Tiles, screed, and concrete store heat but release it with a delay, similar to exterior walls. With wood and carpet floors, it’s different, as these floor coverings store less heat and react more quickly to temperature fluctuations. Therefore, the room heats up faster but also cools down just as quickly.

Room size alone is not decisive for how much a room can warm up. Even with the same size, flooring, window size and orientation, shading, and other factors play a crucial role.