Software Help


For further questions, please email:

If your questions relates to a specific project file, please attach the NameOfProject.bld file, so that we can respond promptly.

Online Introductory Course

Introduction à Lesosai 2018 en 10 minutes (French pdf v.2018)

La RT 2005 avec Lesosa (French pdf v.2018)

La RT 2012 avec Lesosai (French pdf v.2017)

Minergie-ECO® avec Lesosai 2016 (French pdf v.2016)

Importer le format gbXML (French pdf v.2018)

Comprehensive assistance

You can see the help provdied with the software in html help.

Lesosai Software Help

Lesosai in YouTube



Lesosai does not open any more, whereas it functioned very well before!

We contacted the developers of Avast and the solution consists in updating the database AND the software. If it is not possible, here detailed instructions how to proceed to solve the problem in this downloadable pdf.

Does Version 2018 open files from versions 2017, 2016 and 2015, 7.0 to 7.4, 6.0, 5.5 to 5.7 and 5.0 ?

Yes the old files can be opened in 7.0 without problem. However, opening them in versions prior to 7.0 produces errors. Warning: for the same values as the original files, it is necessary to open them with the correct version. If it is no longer available, please contact support

Is there an Apple (Mac OS X) version of Lesosai?

There is no specific Mac OS X version of Lesosai. The best solution to use a PC program on an Apple Mac is to install either an emulator or a "Virtualiser", which can recreate a Windows environment within Mac OS X.
According to the OS on your machine, we recommend:

For more information:
Thanks to Paul-Eric Duplain for this detailed information.

Where can I find psi values for thermal bridges?

You can find these values in the Lesosai menu. You can also download the 130 page "Catalogue of thermal bridges" (in french or german) for free: thermal bridges (PDF)

How do I include my company logo in Lesosai?

The logo must be in bmp format, 140 pixels x 34 pixels and have a resolution of 96 dpi.

The help doesn't work!

If you can not see the help you need to install Internet Explorer 5 or higher, or download this file and install the two executables.

I have Windows 95 and I do not see the buttons on the menu!

If you can not see the buttons in W95, you must install Internet Explorer 5 or higher, or download this file helpwin.zipand install the two executables.

Why is the print preview screen not in English?

This screen is generated by Windows, and Lesosai has no control over it.

Losses in the graphs are not equal to the contributions !

Rejected gains, as defined in the EN ISO 13790 standard, are the part of the gains which are not useable to heat the building, for example the solar gain in summer is much more than necessary. The rejected part is defined by the utilization rate of heat gain, which depends on a number of parameters, including:

  • internal and solar heat gains,
  • the heat capacity of the building,
  • the building's insulation,
  • the type of building

SIA380/1 2001 added the effect of heatin regulation; if the heating control is based on outside temperature, only 80% of potential gains can be used.

Technical losses have no influence on the outcome of the energy needs required for supporting SIA380 / 1 and Form E1. It is made only for people who are interested in estimating the primary energy and thus the amount of oil, gas or electricity needed.

        Primary energy (heating) = Useful Fract. x Needs useful heat for heating
        Technical losses = (1 - Useful Fract.) x Needs heat for heating

Lesosai 6 & 7 don't recognise windows in old files from Lesosai 4 !

Indeed, the glazing table was reviewed, and the old names have been changed. If you have multiple *. bld files produced by Lesosai4 to reuse, you should copy the file Table.glz located in the GLZ folder of Lesosai4 into Lesosai5. At the next startup, Lesosai5 will automatically fill its index with the windows Table.gl2 described in Table.glz. These will then be recognized by Lesosai5. You can of course also reintroduce the windows data that is not recognized.


Spontaneous remote support

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Contactez-nous par courriel ou par téléphone, puis télécharger l'application suivante (ne nécessite aucune installation ni aucune autorisation autre que la vôtre).

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