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


  • Lesosai 2019 build 1409 - France (06/03/2019)
    - RT2012 moteur 8.1
    - amélioré la gestion des matériaux
    Minergie A ECO
    - adapté à Minergie 2019
  • Lesosai 2019 build 1408 (27/02/2019)
    Chauffage au sol :
    -blocage du calcul et warning lorsqu’un raccordement entrant/sortant passe par un local qui a déjà un raccordement passant par le 1er local (calcul impossible).
    -Problème erreur lors du rapport résolu
    -Ajouté la surface restante
    -Traité les cas ou on avait des NaN affichés lorsqu’on entrait des valeurs peu plausibles
    -Amélioré les warnings
    - Ajouté valeurs limites pour Minergie 2019 avec SIA380/1:2009
    - Amélioré le rapport LCA
  • Nouvelle base de données des matériaux (25/02/2019)
    Swisspor SA
  • Lesosai 2019 build 1407 (14/02/2019)
    - corrigé la génération de certains rapports (comme PV)
    - amélioré le rapport SIA380/1
  • CECB - xml (13/02/2019)
    Dans le cas des export vers le CECB pour les maisons individuels, dans la zone chauffée le nombre de pièce doit être plus grand que zéro.
  • Lesosai 2019 build 1406 (13/02/2019)
    Rapport Minergie 2019:
    - ajouté le commentaire que la puissance n'est pas demandé
    Chauffage au sol:

    - Améliorations dans le rapport
    - Prise en compte des planchers intérieurs dans le calcul si checkbox « aucun lien, local à la même temperature ».
    - Correction apparition du warning pour la surface (problème de chiffres significatifs)
    - Bloquer la possibilité d’avoir plusieurs boucles automatiques dans le même local. Seule la première boucle peut-être fully auto.
    - Dorénavant la méthode automatique prend également en compte la limite fixée pour les pertes de charge (en plus de la longueur max).

» 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.