Tallinn University of Technology

Simo Ilomets, a PhD student at the Department of Civil Engineering and Architecture of TTÜ School of Engineering, will defend his doctoral thesis "Renovation Need and Performance of Envelopes of Concrete Apartment Buildings in Estonia" on 28 June.

The future of ageing prefabricated concrete large-panel apartment buildings is widely debated in Estonia as well as in neighbouring countries. Recent studies about the current technical condition of these concrete apartment buildings show that the load-bearing structures are generally in a satisfactory condition (except some facades, balconies, awnings, barriers etc.). In total there are about 3000 apartment buildings composed of prefabricated reinforced concrete large-panels (built mostly between 1962 to 1990), from which only less than one-tenth are estimated to have been fully renovated.

The goal of the doctoral thesis was to study the current need for the renovation of the building envelopes (in particular the external walls and its junctions) and the physical performance of walls in the current (not yet renovated) state as well as after renovation. Indoor loads on exterior walls (temperature and humidity), risk for mould growth on the interior surface of the building envelope, the impact of thermal bridges on heat loss, hygrothermal performance of walls before and after renovation and corrosion of steel in reinforced concrete external core of a three-layer wall were determined based on field measurements and computer simulations.

Simo Ilomets says, "In unrenovated apartment buildings, insufficient ventilation was detected in 2/3 of the apartments. Also, thermal transmittance of external wall is unacceptably high in these buildings, causing coldness and draught in the apartments and bringing about unreasonably high heating costs."

However, the main damage is caused by mould growth and surface condensation with the risk of ca 50%. Thermal bridges after adding external thermal insulation constitute 10–34% of the transmission heat loss of all the building envelopes. The exact percentage of thermal bridges in the transmission of heat loss depends on how the thermal bridges of balconies have been solved, whether the windows have been replaced and positioned into the same plane as the additional external thermal insulation or not. If windows are not positioned into external plane and thermal bridges of balconies are not reduced, the thickness of the additional insulation of external walls (e.g. 15 or 20 cm) will become a secondary factor.

According to Ilomets, the doctoral thesis provides convincing evidence that the building envelopes need to be renovated. Improvement of ventilation and additional external thermal insulation of building envelopes are essential in bringing the buildings into compliance with current requirements. Additional thermal insulation eliminates unacceptable thermal bridges, does not cause any problems related to physical performance of the buildings and, in addition, stops degradation of facades. "Renovation can be done only within a limited time-frame due to the huge construction volume and ongoing degradation of the facades," Simo Ilomets asserts.

"In conclusion it can be said that improvement of ventilation and additional external thermal insulation help to extend significantly the service life of our numerous old prefabricated concrete large-panel apartment buildings," Simo Ilomets adds.

The supervisor of the doctoral thesis is Professor Targo Kalamees (TTÜ).
The opponents of the doctoral thesis are Professor Jari Puttonen (Aalto University, Finland) and Dr. Karolis Banionis (Kaunas University of Technology, Lithuania).

The doctoral thesis has been published in the digital collection of TTÜ library: https://digi.lib.ttu.ee/i/?7670

Kersti Vähi, TTÜ Research Administration Office