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, Lenoz® 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 modu 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


  • Jeûne fédéral (14/09/2018)
    le lundi 17 septembre notre bureau en Suisse est fermé.
  • Formations au Luxembourg (06/09/2018)
    Plusieurs cours sont disponibles dans le cadre de la Formation Construction Durable de l'IFSB (Institut de Formation Sectoriel du Bâtiment):
    M4060_La simulation thermique : Utilisation du logiciel LESOSAI et
    création de certificats de performance énergétique suivant la nouvelle règlementation.

    Le premier jour est structuré aussi comme cours "refresh" pour les utilisateurs actuelles de Lesosai.

    Informations: Construction durable - Formation technique - M4060. inscription: html.
    Prochains cours: mardi 23 et mercredi 24 octobre 2018
    C1054 Ponts thermiques : Calcul par les logiciels Flixo Energy Plus et
    Informations: Construction durable - Formation technique - C1054. inscription: html.
    Prochains cours: jeudi 25 Octobre 2018, 1 journée
    C1056 Lesosai & Calcul des besoins de climatisation, risques de surchauffe et simulation horaire.
    Informations: Construction durable - Formation technique - C1056. inscription: html.
    Prochains cours: vendredi 26 Octobre 2018, 4h
  • Lesosai 2018 build 1218 (05/09/2018)
    - correctif Bat. Neuf ECS fact. énergie primaire dans le cas ECS électrique et instantané
  • Lesosai 2018 build 1217 (03/09/2018)
    SIA387/4 et éclairage naturel:
    - Eclairage naturel selon Minergie ECO 2018
    - SIA387/4 addendum 2019
    - Nouveau bld example

    - Amélioré plusieurs aides
  • Workflow de Revit vers les logiciels de calculs énergétiques (24/08/2018)
    Nous avons le plaisir de vous inviter le mercredi 29 août 2018 à 13 heures à un Webinar:

    Workflow de Revit vers les logiciels de calculs énergétiques.

    Webinar de présentation, par des exemples pratiques, des problématiques de modélisation dans Revit pour accéder aux justificatifs énergétiques via les logiciels certifiés et adaptés.

    par Elise Hautecoeur de la société swissBIM

    Vous allez recevoir le lien pour suivre le webinar quelques jours avant l'événement, inscription par messagerie:
  • Lesosai 2018 build 1216 (14/08/2018)
    - amélioré édition Rset

» All News

NEW: Lesosai 2018!

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 ECCB®
  • 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
  • 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
  • Lenoz


  • 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.