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, DDS-CAD, Vectorworks, Sketchup (with Plugin) and Archicad. Work with the BIM logic (Building information modeling)
  • Lesosai allows to do the MINERGIE-ECO®, DGNB®, SBNS, SIA2031 and Effinergie labels®.
  • 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 or with module RT2005/RT2012 France also contain routines for the calculation of photovoltaic systems.
  • Lesosai comunicate with the database MaterialsDB.org and Edibatec
  • Lesosai contains enhanced models of thermal bridges from the SFOE (Swiss Federal Office of Energy) catalogue and communicate with the thermal bridge software flixo energy plus.
  • Lesosai reduces the time taken to create projects: significant financial gains.
  • Lesosai allows to do the labels: Minergie®, Minergie® ECO, SIA2031®, EN 15217, DGNB®, SBNS®, BREEAM®

» 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 include many official meteorological data.

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 SIA180 and EN ISO 13786).

» 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


  • Nouvelle base de donnée des matériaux (09/09/2015)
    Rigips SA
  • logiciels partenaires de Lesosai - flixo energy (09/09/2015)
    Plus de 10% des clients Lesosai utilisent flixo energy pour leurs analyses de ponts thermiques.
    Il est le seul logiciel de calcul de ponts thermiques qui obtient la note "très bon" dans la comparaison présentée dans la Bachelor Thesis au TU Darmstadt.
  • Lesosai 2015 build 919 (08/09/2015)
    * réduit sensiblement le temps de chargement des gros projet
    * réduit de 5 à 20% le besoin de mémoire lors des calculs horaires
    * corrigé un problème apparu en 914
  • Lesosai 2015 build 918 (28/08/2015)
    * Il est possible d'effacer les parois lors de l'importation
    * Editeur de ombrages proches
    * Import de fichier gbXML Archicad possible
    * Ajout du titre V Laheroof
    * Ajout du titre V Module d’appartement Cardonnel
    * Diverses corrections sur les autres titres 5
    * Ajout de la possibilité d’ajouter des Paroi_Ext de type mur/toiture/plancher dans les Espaces tampons solarisés (Serres)
    * Ajout des facteurs solaires dans les caissons de stores (reprise des FS de l’enveloppe parente ou définition de FS différents)
    * Ajout des facteurs solaires dans les portes
    * Ajout des facteurs solaires dans les surfaces particulières (reprise automatique des FS de l’enveloppe parente)
  • Lesosai 2015 build 914 (29/07/2015)
    * Le moteur de calcul horaire de Lesosai 2015 est accepté par le BRE pour les certifications BREEAM
    * Lesosai 2015 et 7.4 tournent sous Windows 10
    * Correction de quelques bugs de création du xml RT2012
    * Démarré la certification bisannuelle de la RT2012
    * Mise à jour Edibatec
    Module photovoltaïque (PV):
    * Comparé les résultats avec PVSys, les résultats dans Lesosai sont environs de 6% sous estimés, compatibles avec une méthode de calcul simplifiée
    * Amélioré la position du soleil
    Calcul horaire:
    * amélioré les textes
    * amélioré l'aide
    * Analyse automatique des ponts thermiques (pieds de façade et plafond/façade)
    * Calcul ombrages proches (disponible dès la prochaine mise à jour, fin du mois d'août)
    * La surface de référence énergétique doit être calculé hors fichier gbXML
  • Label BREEAM (28/07/2015)
    Le calcul horaire de Lesosai 2015 est accepté par le BRE pour les certifications du label BREEAM.

» 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
  • DGNB Certification
  • Pre-completing the Minergie® file
  • Exporting ECCB®
  • SIA380/4 Lighting
  • SIA382/2 -SIA2044 Power, energy requirement and operative temperature (air conditioning)
  • 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)
  • RT refurbishments
  • Ubât, Ubâtréf, Cep, Cepréf, C, Créf, Tic, Ticréf, BBC
  • Standardized reports and XML files
  • Calculations of changes
  • Effinergie Label

And the global calculations methodologies:

  • EN 12831
  • EN ISO 13790, hourly method (heating and cooling needs) and monthly (heating needs)
  • EN ISO 13791
  • Label EN 15217
  • SIA180, EN ISO 13788, EN ISO 6946
  • Building Life Cycle Impacts Analysis
  • PV and solar thermal simulation
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.