Orientation, solar energy transmittance and lambda value
An energy performance certificate describes how much energy a building needs under standard conditions. It helps compare homes and non-residential properties and is required for many construction and property transactions. We prepare certificates for new buildings, existing properties and renovations.
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.
When is a certificate needed?
Common situations include new construction, certain extensions and major renovations, as well as the sale or letting of a property. Subsidy applications may also require a certificate. For sale and letting, the certificate presented generally must not be more than ten years old; statutory exceptions apply.
What does it tell you?
Key figures include heating demand (HWB), primary energy demand, carbon emissions and the overall energy efficiency factor (fGEE). Heating demand relates mainly to the building envelope; fGEE also reflects building services. The figures are based on standard usage and do not predict the occupants’ actual energy bills.
What documents are required?
Floor plans, sections, elevations, information about walls, roofs and windows, and details of heating, hot water and ventilation are useful. If records for an existing building are incomplete, the construction can be assessed and missing information clarified.
For renovations, a comparison between the existing and planned building may be useful or required for funding. Submission and registration rules vary by federal state.
Official information: General information on energy certificates at oesterreich.gv.at