LESOSAI: 30 years !!

At a glance

Lesosai 7.4 is software for the certification and thermal balance calculation of buildings from 1984 containing one or more heated or cooled zones. It is designed primarily for building engineers, HVAC engineers and architects.

The software can be used in the following languages: French, German, Italian and English. It can use many calculation methods, which can be selected one after another. (see "Countries and Standards" below).

New features

  • Lesosai 7.4 import gbXML file format that is generate by Autodesk Revit, Sketchup (with Plugin) and Archicad (with Plugin 1 / Plugin 2). Work with the BIM logic (Building information modeling)
  • Lesosai 7.4 allows to do the MINERGIE-ECO® 2011 - 2012 label.
  • Lesosai 7.4 includes a wizard that allows you to quickly model a building, ideal for pre-projects and renovation diagnostics. It is now easier and faster !
  • Lesosai 7.4 includes the module Polysun Inside®, for the simulation, caluclation and dimensioning of solar thermal systems. Lesosai with the modul hourly calculations & SIA380/4 or with module RT2005/RT2012 France also contain simple routines for the calculation of photovoltaic systems.
  • Lesosai 7.4 contains enhanced models of thermal bridges from the SFOE (Swiss Federal Office of Energy) catalogue.
  • Lesosai 7.4 reduces the time taken to create projects: significant financial gains.

» Full list of new features

Complete software

Lesosai 7.4 allows the calculation of environmental impacts of the energy consumption, taking into account the energy used in the building, but also the building's construction materials (Life Cycle Impacts Analysis / Environmental Assessment). This calculation is based on a building life cycle approach, and uses the list of impacts maintained by KBOB (extracted from the EcoInvent database), and the methodology conforming to Swiss Draft Standard SIA2032 (Life Cycle Impacts Analysis complete with ECO+® module).

To calculate the heat transfer coefficient (U-value) we have integrated the software USai, which allows the creation of constructions and materials while controlling condensation. It also allows you to synchronise the database with those of the many materials producers who participate in the materialsdb.org project.

To simulate buildings anywhere in the world, Lesosai includes the meteorological data generator, Meteonorm®.

Lesosai can also calculate required heating power, follwing EN 12831 and SIA 384.201by zone or by room. The hourly calculations following EN ISO 13790 are validated with the help of tests follwing EN 15265. Lesosai offers the possibility of calculating the thermal inertia of the buidling by introducing layers of walls (calculation possible under the standard SIA382/1).

» Full list of features

Cutting edge software

The developers of Lesosai continually monitor new regulations and standards, and are constantly incorporating new features. The Lesosai user-experience is constantly being optimized to be as quick and easy as possible. The software was developed with support from several institutions and businesses, notably the Solar Energy and Building Physics Laboratory (LESO-PB) of Ecole polytechnique fédérale de Lausanne (EPFL).

» Institutions and Businesses credited


  • Comparaison entre logiciels SIA382/2-SIA2044 (18/12/2014)
    Nous venons de finir la première phase de tests SIA2044 gérée par la HES de Lucerne. Nous avons comparé les résultats des calculs entre Lesosai, Tectool et Plancal et adapté les logiciels.
    Pour Lesosai 7.4 (à partir du build 871) le changement le plus important a été le calcul de la température Tem qui est maintenant faite à partir des surfaces brutes et non plus des surfaces corrigées par le facteur introduit dans les locaux.
    Un rapport (en allemand) sera publié dans les prochaines semaines.
  • Lesosai 7.4: build 871 (18/12/2014)
    - adapté aux exigences DGNB le calcul des couches
    - changé le calcul du Tem (voir news logiciels SIA2044)
  • Quels labels et normes ECO sont possibles dans Lesosai? (10/12/2014)
    Lire dans le FAQ du site Lesosai le tableau d'explications:
  • Nouvelle base de donnée des matériaux (27/11/2014)
    Isover SA
  • Lesosai 7.4: build 869 (21/11/2014)
    Calcul horaire:
    * amélioré gestion mémoire, il est possible de lancer le calcul de 400 locaux en parallèle
    * amélioré représentation résultats ventilation
    * corrigé bug ouverture fenêtre et bouche hygroréglable simultané
    * ajouté Titre V: Système Biofluides ERS
    RT rénovation:
    * amélioré le rapport
    * corrigé bug du rapport
  • Nouvelle base de donnée des matériaux (20/11/2014)
    Fixit SA

» All News

NEW: Lesosai 7.4 !

Lesosai 7.4
Free Download !

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Lesosai 7.4: » Specifications | » New Features

Why buy Lesosai if I am…
Countries and Standards

Lesosai 7.4 can perform calcluations under the following standards and performance tests :


  • SIA380/1 2007 and 2009
  • MINERGIE-ECO® Certification
  • Adaptation for pre-completing the Minergie® file, version 10a, 11a and 12
  • Exporting ECCB®
  • SIA380/4 Lighting
  • SIA2044 Useful energy requirement and operative temperature
  • SIA380/4 Ventilation
  • Summer overheating
  • SIA384.201 heating power
  • SIA 2031 Primary energy, CO2, air-conditioning (using values from SIA 380/4 and SIA 2024)
  • SIA 2032 Grey energy
  • SIA 2023 window natural ventilation
  • SIA 2028 Official Swiss meteorological stations


  • Calculation of Qh
  • Primary energy and CO2 calculation
  • Energy Passport


  • RT2012
  • RT2005 motor TH-C-E
    (sheet for use)
  • Ubât, Ubâtréf, Cep, Cepréf, C, Créf, Tic, Ticréf, BBC
  • Standardized reports and XML files
  • Calculations of changes


  • DLGs 192, DLGs 311 and calculation of Cd following law 10 (2008-2010 values)

And the global calculations methodologies:

Other software and sites
  • USai: Calculation of the U-value follwoing EN ISO 6946 and SIA180, of U-dynamic, and condensation.

  • ECAT: Adapation of Lesosai for the United Kingdom.