What is WIS

WIS is a uniform, multi-purpose, PC based European software tool to assist in determining the thermal and solar characteristics of window systems (glazing, frames, solar shading devices, etc.) and window components. The tool contains databases with component properties and routines for calculation of the thermal/optical interactions of components in a window.

Development of WIS

The original WIS tool has been developed in the WIS project (2004-2006). The new version of WIS is a product of the WinDat European Thematic Network. Read more about the WIS development team.


WIS contains features often not found in other software packages including routines for the characterisation of the performance of solar shading devices and ventilation in glazing cavities. WIS enables calculations according to the latest (draft) European standards, calculations using advanced routines for innovative products and customised calculations using appropriate routines such as for determining window properties under specific design conditions. WIS is a user-friendly tool, prepared for a wide variety of users including: consulting engineers, manufacturers, building designers, researchers and those involved in standardisation, building regulation and education. It has been developed with an open, object-oriented structure to enable it to respond to future developments.

WIS as platform

Through its variety of calculation routines and databases, WIS forms an ideal platform for bringing together international research on innovative window systems and contributes to an effective and coherent dissemination of research results. Similarily, there is a close interaction between the development of WIS and European standardisation activities within the framework of CEN.


The thermal and solar properties of a window system are a function of the composition of a number of components and the assumptions concerning its environment.

The main components are the transparent part and the window frame. The transparent part consists of panes, gas or air filled gaps and shading elements parallel to the panes. In case of a temperature difference between inside and outside, heat will be conducted through the transparent part by conduction, convection and thermal (IR) radiation. The panes and shading elements transmit, absorb and reflect solar radiation. Absorbed solar heat is in its turn transported to inner and outer surface of the system by conduction, convection and thermal (IR) radiation. In particular the shading elements will to some extend trans­mit thermal radiation and thermally driven or forced circulating air.

Calculated properties

The main properties of a windows system that are calculated in WIS are:

  • Geometric factors (Projected Frame Area, Visible Area Transparent System & Frame Perimeter Length)
  • U-value
  • g-value
  • solar direct transmittance, light transmittance and UV transmittance
All these properties are calculated as a function of the multi-glazing unit, the frame and the properties of the spacer/edge.

The main calculated properties of a multi-glazing unit are the U-value, solar factor (g-value), (direct) solar, visual and UV transmittance and the colour rendering index.

Ray-tracing calculations are possible for both slatted type blinds (such as Venetian blinds and louvers) and for pleated blinds. Instead of one shading category (venetian blinds), WIS now included 4 different types of scattering layers:
  • Slatted type blinds (venetian and louvers)
  • Pleated blinds
  • Roller blinds and screens
  • Generic diffusing devices (such as diffusing panes and other scattering devices not belonging to one of the other categories
WIS Development team

See The WIS software development team

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