Can a house insulated with EPS still overheat?

Once the interior has heated up, insulation can also slow the release of heat to the outside. A way of removing the excess energy is therefore needed. This does not indicate a defect in the polystyrene. It shows that summer comfort requires a whole set of measures. The choice of wall material is only one of the decisions.

A large glazed area exposed to the sun can deliver considerable solar gains. Its area, orientation, glass properties and shading matter. Thicker EPS on the wall will not stop radiation passing through the window. Before changing the insulation, it is therefore worth observing at what time of day and in which rooms the biggest problem occurs.

Heat is also supplied by people, cooking, lighting and appliances. In a loft, the influence of the heated roof and roof-slope windows is added. In a house with an intensively used kitchen or computer equipment, internal gains can be significant even after sunset. The assessment should take into account how the rooms are actually used.

It is best to limit gains before the radiation warms the interior. Suitably selected external shading, shading devices and the right choice of glazing help. Their effect depends on the orientation and time of day. A fixed canopy that works when the sun is high may provide less protection against low rays from the west.

Internal blinds improve conditions at the window, but some of the energy will already have passed through the glass. It is worth planning to control the shading before the room heats up. Covering the window only once the temperature has risen removes the cause with a delay. Mounting shading on an insulated façade also requires correct fixing and sealing.

Air exchange can remove heat when the outside air is sufficiently cooler. Night or morning ventilation is often beneficial if conditions allow. Opening windows during the hottest part of the day, by contrast, can introduce additional energy. The decision should be based on the temperature on both sides, not only on a feeling of stuffiness.

Hygienic ventilation must also work in summer. The required air exchange must not be blocked in order to keep the interior cool. In a mechanical system, the summer mode and actual performance must be checked. A heat-recovery bypass function is not the same as air conditioning. During a long heatwave, active cooling may be needed.

No. Lambda describes heat conduction through a material under specified conditions. It does not take into account the size of windows, solar gains, ventilation or the thermal capacity of the structure. Two walls with a similar U-value can respond differently over time if their construction differs. Likewise, two houses with identical EPS can have different indoor temperatures.

The mass of walls and ceilings can limit rapid fluctuations, but it must be able to release the accumulated heat. A summer assessment requires analysis of variable conditions, preferably for the whole building. It is not worth choosing a material on the promise that a particular lambda will ensure a specific temperature in every bedroom.

Start with simple observations. Note the temperatures in the morning and evening, the position of the sun and how you ventilate. Check the condition of the roof insulation and continuity at the details. Then compare the effect of shading, limiting gains and removing heat. Not every improvement requires adding another layer to an already well-insulated wall.

EPS boards for the thermal protection of buildings are produced, among others, by Austrotherm, Swisspor, Yetico and Arbet. Their parameters are selected for the building element, while summer comfort is assessed for the whole house.

If you are planning a larger renovation, combine the decisions on insulation, windows and ventilation in a single study. The expenditure then complements one another. The aim is to limit the inflow of heat during the day and to ensure effective cooling when conditions allow, without worsening indoor air quality.