Orientation, solar energy transmittance and lambda value
In Vienna, energy performance certificates are relevant to houses, flats, apartment buildings and commercial properties. We prepare them for new construction, existing buildings and renovation projects.
A building’s orientation tells you which direction its windows and façades face. This matters because sunlight through south-facing windows can help warm a room in winter, but it can also make it too hot in summer. Good shading makes a difference. The solar energy transmittance (g-value) tells you how much of the sun’s energy passes through the glass into the room. A lower g-value lets in less solar heat; a higher one lets in more. The lambda value describes how easily heat passes through an individual building material. The lower the value, the better that material insulates. What matters in practice is how the glazing, insulation and construction work together.
New buildings and planning applications
Vienna’s building regulations determine whether a certificate is required for a given application. Additional evidence on thermal protection, acoustics or building services may be needed. Where electronic submission is required, the city uses the WUKSEA system; the registration should be considered early in the project.
Sale, letting and renovation
A valid certificate generally has to be presented when a property is sold or let. For renovations, the scope of work matters: replacing a single component can involve different requirements from a major renovation. Some funding programmes request calculations for both the existing and the proposed condition.
What do we need to get started?
Plans, sections, elevations and information about the building envelope, windows, heating and domestic hot water. For older buildings, we check which details are available and which need to be recorded.
Official information: City of Vienna: energy certificate and building-physics submission