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Fair roof window marketplace
with good reputation

Consumers need to be able to trust on product declarations

Above all else, the VELUX Group wants a fair roof window marketplace with a good reputation, so that consumers can rely on the Uw-value or thermal performance of the roof windows they buy as holding true.

The VELUX Group believes that transparency about the status of Uw-values is paramount to creating a fair and level playing field in the roof window industry, so that consumers can rely on the declared values. Therefor VELUX has made the results of the testing public available.

Comprehensive testing for compliant and well-functioning market

Comprehensive testing is necessary in order to secure compliance between the actual and declared thermal performance of roof windows and to ensure a well-functioning market that has transparent and universal standards for the benefit of consumers.

Therefore, the VELUX Group set up independent testing of its own and competitors’ products between 2016 and 2018, which were continued in 2019, The testing in 2016-2018 involved 222 tests of competitors’ roof windows and 55 tests of VELUX roof windows. The new round of testing in 2019 involved 55 tests of competitor roof windows and 16 tests of VELUX roof windows. 

The tests of competitors’ products showed discrepancies between the declared Uw-values and the Uw-values of most of the actual windows tested. Therefore, the test results are brought to the attention of competitors, as well as relevant market surveillance authorities, to which complaints are filed by the VELUX Group.


The VELUX Group has instigated the global consultancy Navigant to independently source and organise testing of different roof window types from four European manufacturers, including its own. The roof windows were purchased randomly at different dealers in different countries over a 4 years period. The tests were carried out by two European notified test institutes and the results presented give a full and trustworthy picture of the tested products’ actual Uw-value performance. 

The roof windows were first tested at ift Rosenheim in Germany and thereafter a sample of them were sent for control testing at Centrum Stavebního Inženýrství a.s. in the Czech Republic.

Both institutes are notified bodies for testing roof windows.

The tests were carried out in accordance with the European standard for testing roof window Uw-values (EN ISO 12567-2), using the reference size, and the roof windows were installed in test boxes, in compliance with the respective manufacturers’ guidelines.

The VELUX Group believes that the test results presented by the global consultancy Navigant give a complete and trustworthy picture of the tested products’ actual Uw-value performance.

The testing procedure for tests during the next years will follow the same procedure as above.