Building Energy Software Tools
Formerly hosted by US Dept. of Energy    


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Lesosai is software for the certification and thermal balance calculation of buildings containing one or more heated or cooled zones. It was created in 1984 and continuously imporved since then.
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).
It is available from
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 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 384.201 by zone or by room. Lesosai offers the possibility of calculating the thermal inertia of the buidling by introducing layers of walls (calculation possible under the standard SIA382/1).

Expertise Required: 

The program is designed primarily for building engineers, HVAC engineers and architects.
Understanding French, German, Italian or English is necessary.
Lesosai includes a wizard that allows to quickly modelling a building, ideal for pre-projects and renovation diagnostics.


Several thousands are sold today, mainly in Switzerland, France, Italy, Luxembourg and United Kingdom.


Building envelope elements dimensions and thermal characteristics. The latter can be entered when known, or calculated on the basis of their structure. Occupancy data (defauld values are provided if necessary)
When needed (e.g. for hourly calculations, energy use for lighting and appliances, or room-by-room calculations) internal walls characteristics.
Meteo data and buildign materials characteristics are included in a database.
Also Lesosai imports gbXML file format and works with the BIM logic (Building information modeling)


Building heat balance, energy use for heating, hot water, lighting and other appliances.
Heating power room by room or for the whole building
Official reports on heating energy use for Switzerland, italy, France and Luxembourg.


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).
Its user interface is user friendly. The basic uses can be learnt in 30 minutes.

Major Capabilities: 
Load Calculations
Code Compliance
Life Cycle Analysis
Building Type: 
Multi Family
Mac OS X
Free To Try
Help and Support: 
Free Email Support
Free Phone Support
Subscription Email Support
Subscription Phone Support
Last Software Update: 
16 September 2015
Last Entry Update: 
24 September 2018
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