Building automation system (200, 300, 400, 600), comprising: - at least one first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) comprising at least one actor (218, 318.1, 318.2) and/or at least one sensor (320.1, 320.2), - wherein the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) comprises at least one first function module (222.1, 322.1), - wherein the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) is configured to operate in accordance with the first function module (222.1, 322.1) in order to provide at least one first function, - at least one peer-to-peer network (226, 326, 426, 626) comprising at least one peer-to-peer application (224, 324, 424, 524), - at least one peer-to-peer module (230, 330) assigned to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) and configured to communicate with the peer-to-peer application (224, 324, 424, 524), - wherein the peer-to-peer application (224, 324, 424, 524) comprises at least one controlling means (227, 327, 527) configured to provide at least one second function module (222.2, 322.2) to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) by means of the peer-to-peer module (230, 330) assigned to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3), and - wherein first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) is configured to operate in accordance with the second function module (222.2, 322.2) in order to provide at least one second function, - characterized by the following features: the peer-to-peer application (224, 324, 424, 524) is configured to generate a function transaction agreement at least about the provision of the second function module (222.2, 322.2) to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3). - at least one first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) comprising at least one actor (218, 318.1, 318.2) and/or at least one sensor (320.1, 320.2), - wherein the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) comprises at least one first function module (222.1, 322.1), - wherein the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) is configured to operate in accordance with the first function module (222.1, 322.1) in order to provide at least one first function, - at least one peer-to-peer network (226, 326, 426, 626) comprising at least one peer-to-peer application (224, 324, 424, 524), - at least one peer-to-peer module (230, 330) assigned to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) and configured to communicate with the peer-to-peer application (224, 324, 424, 524), - wherein the peer-to-peer application (224, 324, 424, 524) comprises at least one controlling means (227, 327, 527) configured to provide at least one second function module (222.2, 322.2) to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) by means of the peer-to-peer module (230, 330) assigned to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3), and - wherein first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3) is configured to operate in accordance with the second function module (222.2, 322.2) in order to provide at least one second function, - characterized by the following features: the peer-to-peer application (224, 324, 424, 524) is configured to generate a function transaction agreement at least about the provision of the second function module (222.2, 322.2) to the first appliance device (204, 304.1, 304.2, 304.3. 404.1, 404.2, 404.3).