Whereas addresses are intended for public entrances only, sub addresses are used whenever there are multiple private entrances beyond a public entrance.

Sub addresses are important to identify such things as apartments within residential towers, shops along the facades of commercial buildings, lots within industrial zones or ports and villas within residential compounds.

While this element is one step beyond the address unit number and thus not the core of the responsibility of the national addressing organisation, it is of importance to the daily operation of services.

The National Addressing System includes the following code list which is considered extensible, i.e. elements can be added to it as per demand:

• Villa (as in a compounds, i.e. a walled development with controlled access and many individual housing units inside)
• Apartment (as in units inside multi-dwelling buildings)
• Shop (as in commercial and mixed commercial-residential buildings)
• Space (as in industrial facilities)
• Office (as in office buildings)
• Room (as in hotels, accommodation)
• Suite (as in hotels, accommodation and office buildings)
• Multi-dwelling unit (as in residential buildings, used whenever a sub address parent to other sub-addresses)
• Other

The old addressing system that is in place today is in use in certain legal documents, including but not limited to tenancy contracts. In these documents, block numbers, way numbers, address unit numbers and sub addresses are included to help identify the locations and spaces.

When the new addressing system is implemented, ways will in all cases be assigned new street names, and address units may - and in most cases will - be assigned new numbers.

When this happens, the address information included in the legal documents and the addresses evident from signage in the streets and on the buildings will no longer correspond to each other.

This problem must be dealt with in one of two ways, as described below.

At the time of physical implementation of the national addressing system, the old address unit numbers and way number of each address unit will be recorded and added to the data. That way there will be a link between address units in the old system and address units in the new system.

For sub address number plates, the initial implementation of the new addressing system will not touch these. That is, they will neither be added nor removed. Instead, a web service will be made that allows sub addresses to be created for an address unit. That way, creation of sub addresses and mapping of these from the old to the new addressing system can be made part of a variety of licensing and permitting processes already in place in the municipalities and by the service providers.

That way, over time, we can accomplish a complete collection of sub addresses for all buildings and prevent the lack of sub addresses from becoming a show-stopper in services provided to the general public. When a new sub address unit is created, the owner or tenant becomes responsible for placing signage.

Signage must correspond to specifications provided by the addressing organisation.

This alternative is highly impractical and laborious and is not recommended. It is however a technical possibility and is included in this document for that purpose.

Sub addresses are initially created at the same time as creating address units. This requires a comprehensive survey of all buildings to capture all shops and spaces with entrance directly from the street as well as a complete internal inspection of all buildings to determine the floor and unit numbering schemes employed for each building and record all internal units.

All the data will be added to the addressing database and assigning an address to e.g. a tenancy contract will be a matter of hierarchically selecting address elements from drop down boxes or typeahead input fields where the user specifies wilayat, street name, address unit number and finally can choose sub address.

However, since a field survey is not conducted every time a shop is partitioned or a space leased, the update of the model will still require integration with the permitting and licensing applications in order to maintain sub addresses.

While preexisting and correct sub address data being available in the system would be convenient from a third party integration point of view, implementing such a solution in practice would be extremely costly and laborious.