LESOSAI: 30 years !!

At a glance

Lesosai 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 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 allows to do the MINERGIE-ECO® 2011 - 2012 label.
  • Lesosai 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 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 contains enhanced models of thermal bridges from the SFOE (Swiss Federal Office of Energy) catalogue.
  • Lesosai reduces the time taken to create projects: significant financial gains.

» Full list of new features

Complete software

Lesosai 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


  • USai Revit Plugin (28/03/2015)
    une version de USai (le moteur de la version 4) adapté pour le logiciel de CAO Autodesk® Revit®.

    Pour plus d'informations
  • Lesosai 2015 build 909 (27/03/2015)
    Présentation des nouveautés au 27.03

    Erreurs dans l'arborescence
    - amélioré la visibilité
    - corrigé création des stores lors de la re-importation avec changement d'affectation
    - ajouté valeur limite Canton Bâle rénovation (90% x 125% Qhli)
    Rapport EN-5:
    - corrigé charges thermiques internes si rénovation
  • Lesosai 2015 build 908 (24/03/2015)
    - amélioré le rapport ponctuel
    - dans le rapport mis Uw sp
    Label LCA:
    - enlevé SRE non LCA
  • USai Revit Plugin (18/03/2015)
    Avec la société Mensch und Maschine (MUM) nous avons développé une version de USai basée sur la version 4, adaptée pour le logiciel de CAO Autodesk Revit® et compatible avec Lesosai 2015.
    Pour plus d'information utiliser ce lien (version test disponible): USai Revit Plugin
  • Lesosai 2015 build 907 (16/03/2015)
    Présentation nouveauté
    GBXML :
    - Importation des constructions USai Revit Plugin
    - Amélioré la gestion des erreurs
    - La géométrie intérieure des locaux n’est plus nécessaire pour charger un projet gbXML.
    - Importation des constructions gbXML standard
    · Modifié pour importer selon plusieurs formats
    · Importation des valeurs-U fixes si les couches ne sont pas définies
    ·Importation de l’absorption
    Groupe :
    - Liste des locaux du groupe avec possibilité de les ordonner dans plusieurs normes
    - Amélioré le rapport des ponts thermiques
    - Amélioré le rapport Minergie
    - valeur limite par défaut 31/12/2016
    - corrigé erreur de format dans le label
    - pour export fixé maximum isolant à 0.095
    - corrigé quelques points dans le rapport
  • Cours Lesosai (02/03/2015)
    09/03 cours de base
    09/03 cours avancé
    18/03 Flixo energy plus
    20/03 SIA380/4
    24/03 Labels ECO (Minergie, DGNB,...)
    26/03 SIA382/2-SIA2044 climatisation

» All News

NEW: Lesosai !

Free Download !

Downloads page

Lesosai: » Specifications | » New Features

Why buy Lesosai if I am…
Countries and Standards

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


  • SIA380/1 2007 and 2009
  • MINERGIE-ECO® Certification
  • Pre-completing the Minergie® file
  • 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.