The city is heating up!

There is a great deal of discussion about the rise in city temperatures. According to an article in the press from 25 July 2019, we are heading for an increase in the average daytime temperatures of Vienna city centre by up to 7.2° on sunny days.


What can we, as planners, therefore recommend:

The use of green roofs

Green roofs have many advantages: they not only improve the overall air quality in cities, but also create new habitats for insects and small animals. The thin soil structure of just over 8 cm in extensive constructions serves not only as additional insulation (both winter and summer), but also allows for the absorption of rainwater thereby relieving wastewater systems. Through the evaporation of rainwater, the room temperature of the directly underlying rooms is able to become significantly cooler in the summer.

Moreover, new studies show an increased efficiency of photovoltaic systems through the cooling of the roof surfaces.

The service life of the roof is significantly increased because of the mechanical protection and absorption of UV radiation.

There is no major effort expended in the case of an 'extensive' green area (soil structure min. 8 cm) because very robust plants are used, which already subsist on low water volumes.

More effort will be expended in the long run for 'intensive' green areas (soil structures min. 30 cm) due to the management of the green spaces. However, this creates usable places for building residents (for example: gardens on top of hospitals and office buildings).

Façade greenery

Façade greenery is also an effective way to improve city climate. Façade plants likewise provide habitats for animals and insects. Furthermore, you can reduce the heating and cooling loads through an insulation effect of evergreen climbing plants.

Sun protection and window blinds systems

The best solution for darkening rooms during the day is externally mounted roller shutter boxes. Sunbeams are completely blocked out – window panes cannot warm up and thus cannot emit any heat into the room's interior.

Window film is yet another good and inexpensive alternative for avoiding annoying sun glare (bouncing onto computer screens, amongst other things).

The replacement of old construction or casement windows can also significantly reduce the heating and cooling loads.


Façade painting with high reflection radiation

Even the colour of the building can significantly affect the temperature of the interior. A white façade heats up considerably less than a dark brown or a black house façade. You can often see this in southern countries such as Tunisia.

Construction method

In this respect, you need to weigh up what is useful and technically possible proportionally in terms of thermal insulation and heat storage. The old Viennese apartment complexes are built with massive outer walls up to 90 cm thick. In this case, the proportion of possible heat storage is high, while the thermal insulation rather low. As long as the heat can be released back here at night, this is a positive effect for summer and transitional days.

However, when the heat storage capacity is exhausted and can no longer give off any more heat at night, the outside air continues to warm up and results in overheating issues.

In order to use the heat storage effect, the massive structural components are in the meanwhile thermally activated. Heating or cooling elements are installed here in the concrete walls or ceilings, and a temperature exchange between the building and the subsoil is arranged via thermal pumps and depth probes.

Air conditioning systems

Air conditioners are real energy guzzlers and only partially sustainable, because the recooling unit gives off heat to the outside. Although they cool the air inside a room, they blow out hot exhaust air and thus contribute to 'urban warming'. At present, mobile air conditioning systems in particular (together with gas boilers) cause CO2 poisoning because they generate low pressure in the room by blowing out the room air. Combustion occurs only partially and thus the combustion gases, which should actually escape through chimney flues, are sucked back into the room.

In modern new buildings, cooling is often already included and combined with heat recovery units in certain situations to generate hot water (for instance) with the gained energy.

We are happy to support you with calculating the cooling load and planning sustainable solutions!


Find out more in the following articles:

Artikel Wiener Zeitung - Gut gekühlte Zukunft vom 25. Juli 2019

Mit 8 Schritten zum grünen Dach

Förderantrag Dachbegrünung Stadt Wien

Die 10 besten Tipps zur Abkühlung



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