The voluntary technical approval (ATG) provides technical advice, including a description and the technical characteristics. An ATG is a favorable assessment of one specific construction product from one manufacturer for a specific application. It must enable the user to check the conformity of the products delivered at the construction site with the existing approval. ATGs are delivered for products for which no product standards exist. It therefore mainly concerns systems, innovative products and products that consist of multiple components. An ATG is in principle delivered on the basis of an approval guideline. Such guidance is drawn up by experts from the Belgian Union for technical approval in construction (UBAtc) and forms an assessment basis for construction products.

On top of that, certification usually occurs, which means the WOOD.BE / BCCA with an established frequency exercises external supervision over the conformity of the production with the published approval. This review or check is described in a convention that is drawn up when the ATG is granted. This agreement indicates how the manufacturer organizes his own control of the production and which external tests will be carried out.