The Building Decree 2012, which establishes a duty to connect to heating grids, entered into force on 1 April 2012. The principle of equivalence in the Building Decree 2012 provides for the possibility of an alternative to this obligation: instead of connecting to a heating grid, an equivalent solution may be applied which would nullify the obligation. This would make investments in a heating grid uncertain, because it would no longer be clear ahead of time whether the minimum number of connections required for the operation of a heating grid would ever actually be met. The Decree of 11 February 2013 amending the Building Decree 2012 (Bulletin of Acts, Orders and Decrees 2013, 75) introduces the Heat Plan (Warmteplan): the possibility for forcing connection to a heating grid until the number of connections required for economically feasible operation of the grid is reached. A Heat Plan must indicate the area involved, the number of connections needed to operate the heating grid economically feasible and the degree of energy efficiency and environmental protection that can be achieved by connecting to the heating grid. A Heat Plan has a maximum effective term of ten years. The municipality verifies the equivalence of an alternative using the energy efficiency and the protection of the environment as described in the Heat Plan.