This part of ISO 17484 specifies the recommended practice for the installation of multilayer pipe systems in accordance with ISO 17484-1. It is applicable to pipe systems used in buildings to supply gas with a maximum operating pressure (MOP) up to and including 5 bar. This part of ISO 17484 specifies common basic principles for indoor gas systems. Users of this part of ISO 17484 should be aware that more detailed national standards and/or codes of practice can exist in ISO member countries. These existing regulations, as well as new national regulations, take precedence over this part of ISO 17484. It is intended to be applied in association with these national standards and/or codes of practice setting out the above-mentioned basic principles.