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. Simple and effective, the monitors adapt the required information to the needs of the chosen standard or label. 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), Rhino 3D/Grasshopper with plugin and Archicad. Work with the BIM logic (Building information modeling)
  • Lesosai allows to do the MINERGIE-ECO®, DGNB®, BREEAM®, 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 Rooms - sizing hot/cold - comfort – electr. 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.

» 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 Standard SIA2032 (Life Cycle Impacts Analysis complete with ECO+® module).

Compatible BEM (Building Energy Modelling) via the gbXML format.

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 and SIA2044 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 données des matériaux (05/06/2019)
    Fixit SA
  • Long weekend fermé (29/05/2019)
    Le bureau E4tech Software SA sera fermé du 29 au 30 juin 2019 compris
  • Lesosai 2019 build 1417 (29/05/2019)
    - Béton armée libre (exemple par le KBOB Rechner)
    - Amélioré la base de donnée de béton
    - Amélioré le pdf du ECO label
    - Amélioré l'intro des données dans le local
    - Amélioré la traduction en italien
  • Lesosai 2019 build 1416 : CECB (22/05/2019)
    - Amélioré l'export des variantes pour aider le CECB à lier les éléments avec la base
    - Corrigé l'export de la SRE des écoles en multizone
  • Lesosai 2019 build 1415 - important (09/05/2019)
    - Correctif SIA mars 2019, valeur cible 70% de la valeur limite
    Chauffage au sol
    - Correction dans le rapport (filtrage des locaux par groupe)
    - Résolution d’un problème en calcul automatique lorsque le local était lié à un modèle du dépôt
    - Correction de la prise en compte des facteurs b dans le calcul de Ath pour Minergie 2017/2018 lorsque SIA380/1:2016 est sélectionné. Calcul erroné entre build 1408 et 1414
    - Amélioration de la visualisation lorsque les coordonnées des objets 3D sont « extrêmes »
    - Correction des valeurs d’impacts des bétons pour KBOB 2016. De nouveaux matériaux bétons ont été créés dans la base de données. Les anciens bétons sont toujours présents mais sont définis comme « plus en vente »
    - Les pages de commentaires sont dorénavant affichées correctement si l’ordre des commentaires a changé
    - Traductions ajoutées dans la fenêtre d’export pdf
    Gestion des matériaux
    - Résolu problème lorsqu’on double-clique sur un matériau qui possèdent des couches de différentes épaisseurs
    - Les matériaux n’étant plus en vente sont dorénavant affichés en gris et en italique
    Aides et pdf
    - Adapté le pdf MoPec 2014 / Minergie 2019
    - Amélioré l'aide
  • Lesosai 2019 build 1414 (11/04/2019)
    - amélioré les écrans résultats
    Version 64bit:
    - amélioré la gestion des pointeurs qui pouvaient planter le logiciel
    Polysun :
    - amélioré le rapport
    - re-activé THD pour certains ordinateurs

» All News

NEW: Lesosai 2019

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, 2009 and 2016
  • MINERGIE-ECO® Certification
  • DGNB Certification
  • Pre-completing the Minergie® file
  • Exporting CECB®
  • SIA385/2:2015 HW
  • SIA380/4 and SIA387/4 Lighting
  • SIA382/2 -SIA2044 Power, energy requirement and operative temperature (air conditioning)
  • SIA385/2 Hot water needs and power
  • SIA382/1 and SIA380/4 Ventilation
  • SIA180 and SIA382/1 Summer overheating
  • SIA384.201 heating power
  • SIA 384.512-515 heating floor
  • 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


  • 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 heating power
  • EN 1264 floor heating
  • EN ISO 13790, hourly method (heating and cooling needs) and monthly (heating needs)
  • EN ISO 13791
  • EN ISO 13370
  • Label EN 15217
  • SIA180, EN ISO 13788, EN ISO 6946
  • Building Life Cycle Impacts Analysis
  • PV and solar thermal simulation
Other software and sites
  • Eco-Sai: Calculation of the U-value follwoing EN ISO 6946 and SIA180, of U-dynamic, and condensation.