HPZ-Walls - High-performance exterior brick walls without additional thermal insulation

Sustainable multi-storey housing made of bricks can only be realised if the strength of thermally optimised vertical coring bricks is tripled. This is to be achieved by changing the hole pattern, namely by reducing the air gap from 8 to 4 mm. A success of the project will form the basis for the realisation of insulation-free, 8-storey residential and office buildings in brick construction.

Short Description

Starting point / motivation

A quarter of all heat flows between the interior and exterior of a building pass through the exterior wall. This illustrates the importance of the exterior wall for the energy demand of a building. Driven by legal regulations on "energy saving and thermal insulation", external thermal insulation composite systems have become established.

Although these fulfil the required thermal insulation properties, they cause air temperatures in neighbourhoods to rise in summer, prevent the extraction of solar thermal energy during the heating season and have to be disposed of as hazardous materials at the end of their relatively short service life.

The monolithic, mineral plastered brick wall, on the other hand, can meet both the sustainability requirements and the high thermal requirements of urban residential and office buildings as long as the architecture, the masonry and the brick are optimised for this purpose. The thermally optimised, highly porous bricks currently available on the market do not have sufficient load-bearing capacity to be able to realise multi-storey residential construction.

Contents and goals

In the project presented here, a macrostructural approach is taken to solve this problem. The load-bearing capacity of the brick is to be increased by reducing the proportion of holes without worsening the thermal insulation properties. This seemingly paradoxical goal has already been theoretically achieved and was patented under the name "TRALAM".

A case study of an 8-storey residential building showed that the load-bearing capacity requirements of a 50 cm TRALAM masonry wall are met for a building height of 22 m. Furthermore, it demonstrated that the heating requirement according to the U-value method corresponds to that of an ETIC system, and that an additional solar energy gain of 10% is achieved via the non-insulated opaque outer surface. To increase the load-bearing capacity without changing the fired clay strength, more clay must be fired and consumed – with all the associated effects on the ecological footprint of production.

In return, the high-performance masonry requires only one third of the building ground and one third of the roof area to create the same living space because the load-bearing capacity of the brick is approx. three times higher and consequently the number of storeys can also be tripled in comparison to actual pure brick buildings.

TRALALM buildings do not require any insulation material, they have significantly extended service life, as the robustness of the brick allows the facade plaster to be renewed after one period of use (reparability), and they use solar energy in winter and reduce overheating in summer.


In order to be able to transfer these promising results to reality, comprehensive experimental verification is necessary. The TU-Graz plans to carry out this project in cooperation with the Austrian brick industry. One of the goals of this R&D project is to carry out a 1-year field test in one of the test houses at the TU-Graz. This test is to determine the actual total energy balance by measurement.

However, the production of the necessary bricks has not yet been tested and is thus a high project risk. This should be minimised by starting the exploratory project presented here as a preliminary step, focusing only on the feasibility of the production and the final optimisation of the brick design and the masonry bond.

Expected results

It is expected that a reduction of the air gap thickness from 8 to 4 mm can be realised in terms of production technology. Laboratory tests and numerical physical simulations will be carried out to determine the mechanical and structural properties to make sure that the follow-up project can be developed in detail. Therefore, approximately 200 prototype quarter bricks are to be produced.

Project Partners

Project management

Graz University of Technology / Laboratory for Structural Engineering

Project or cooperation partners

  • Forschungsverein Steine – Keramik
  • Architekt Horst Gamerith, Em.Univ.-Prof. Dipl.-Ing. Dr.techn.

Contact Address

Graz University of Technology
Laboratory for Structural Engineering
Priv.-Doz. Dipl.-Ing. Dr.techn. Bernhard Freytag
Inffeldgasse 24
A-8010 Graz
Tel.: +43 (316) 873 7050
E-Mail: freytag@tugraz.at
Web: www.lki.tugraz.at