Peer-reviewed articles 17,970 +


Stanislavs Gendelis
•    Prof. DSc. Oleksandr Trofymchuk, UKRAINE 
•    Prof. Dr. hab. oec. Baiba Rivza, LATVIA
Avoiding thermal bridges in the building envelope is one of the key elements for the reduction of energy consumption in buildings. Numerical calculations of heat flux through the joints of building structures are becoming very relevant in the past years due to the EU requirements for nearly zero energy buildings. The most problematic typically is windows installation perimeter, where thanks to fastenings of the frame to the loadbearing structure, linear thermal bridge forms.
The use of numerical calculation of temperature and heat flux fields allows to visualise the thermal bridge effect, as well as to calculate the additional energy losses is such critical places with following recommendation to minimize it. This work focuses on modelling of top, bottom and side thermal bridges in a new window installation in a thermal insulation layer with the variable depth of the installation. Created models allows also to calculate the minimum surface temperature and the dimensionless temperature factor f, both describes the risks of potential condensation formation and mould growth. Calculations are made using Flixo software and according to ISO 10211 standard.
The results of preformed calculations of different installation depths clearly show the optimum of the distance between the main load-bearing wall and window frame. Numerical value of thermal bridge value (or psi-value) at optimum depth may reach even negative values, meaning that the total heat flux for windows and wall connection becomes smaller when they are connected. Overall, the numerical calculations of thermal bridge flux show a wide range of psi-values from 0.025 W/m/K down to -0.005W/m/K for top and side installations. The psi-value for bottom installation with windowsill may be reduced from 0.1 W/m/K down to 0.03 W/m/K. The optimal installation depth is determined as 9…15 cm with essential dependence on the insulation layer thickness.
Assuming that windows are the most thermally conductive building elements, carried out calculations provide information for the engineers in the field building energy efficiency regarding the window installation optimization to reduce the thermal bridge effect and to estimate additional heat losses also numerically at the design stage.
[1] Erhorn-Kluttig, H., Erhorn, H. Impact of thermal bridges on the energy performance of buildings. Information Paper P148 of the EPBD Buildings Platform, 2009.
[2] Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy performance of buildings (recast), Official Journal of the European Union, 153, 2010.
[3] Directive 2012/27/EU of the European Parliament and of the Council of 25 October 2012 on energy efficiency, amending Directives 2009/125/EC and 2010/30/EU and repealing Directives 2004/8/EC and 2006/32/EC, Official Journal of the European Union, 315, 2012.
[4] ISO 10211:2017. Thermal bridges in building construction — Heat flows and surface temperatures — Detailed calculations. International Organization for Standardization, 2017.
[5] Terentjevas J., Sadauskaite M., Sadauskiene J., Ramanauskas J., Buska A., Fokaides P.A. Numerical investigation of buildings point thermal bridges observed on windowthermal insulation interface, Case Studies in Construction Materials, 15:e00768, 2021. doi: 10.1016/j.cscm.2021.e00768.
[6] Sadauskiene J, Ramanauskas J, Seduikyte L, Dauksys M, Vasylius A. A Simplified Methodology for Evaluating the Impact of Point Thermal Bridges on the High-Energy Performance of a Passive House. Sustainability. 7(12):16687-16702, 2015. doi:10.3390/su71215840.
[7] “Triotherm” thermal brackets for External Wall Insulation – Eliminate thermal bridging by reducing Psi. (accessed 1 February 2023).
[8] Kuusk K., Kurnitski L., Kalamees T. Calculation and compliance procedures of thermal bridges in energy calculations in various European countries. Energy Procedia, 132, pp. 27-32, 2017. doi: 10.1016/j.egypro.2017.09.626.
[9] Ratnieks J., Jakovics A., Gendelis S. Long term energy efficiency study on different wall envelopes in Latvian climate conditions, Energy Procedia, 132, pp. 441-446, 2017. doi: 10.1016/j.egypro.2017.09.654.
[10] Ilomets S, Kuusk K, Paap L, Arumagi E, Kalamees T. Impact of linear thermal bridges on thermal transmittance of renovated apartment buildings. Journal of Civil Engineering and Management, 23(1), pp:96-104, 2017. doi: 10.3846/13923730.2014.976259.
[11] “Flixo” – The thermal bridge analysis and reporting application. (accessed 1 February 2023).
[12] Apine I., Birjukovs M., Jakovics A. Comparative assessment of mould growth risk in lightweight insulating assemblies via analysis of hygrothermal data and in situ evaluation. Journal of Ecological Engineering, 20 (11), art. no. 3147, 2019. doi: 10.12911/22998993/113147.
[13] Passive House Component Database. Passivhaus Institut GmbH. (accessed 1 February 2023).
This research was made possible through the postdoctoral project “Analysis of the actual energy consumption of zero energy buildings and the development of the necessary energy efficiency improvement solutions” (
Proceedings of 22nd International Multidisciplinary Scientific GeoConference SGEM 2022
22nd International Multidisciplinary Scientific GeoConference SGEM 2022, 06-08 December, 2022
Proceedings Paper
STEF92 Technology
International Multidisciplinary Scientific GeoConference SGEM
SWS Scholarly Society; Acad Sci Czech Republ; Latvian Acad Sci; Polish Acad Sci; Serbian Acad Sci and Arts; Natl Acad Sci Ukraine; Natl Acad Sci Armenia; Sci Council Japan; European Acad Sci, Arts and Letters; Acad Fine Arts Zagreb Croatia; Croatian Acad Sci and Arts; Acad Sci Moldova; Montenegrin Acad Sci and Arts; Georgian Acad Sci; Acad Fine Arts and Design Bratislava; Turkish Acad Sci.
06-08 December, 2022
Thermal bridge, psi-value, Flixo, numerical calculations, mathematical modelling, optimization, window, building

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