Multiple Residence Data is a dataset maintained by Royal Mail that records the individual flats, apartments, or other separate units that lie behind a single shared postal delivery point. In a typical block of flats, for example, the postman delivers all letters to a communal post box or a single entrance, yet each separate dwelling has its own distinct address. Multiple Residence Data captures these hidden sub-addresses, making them visible in official address records.

What Is Multiple Residence Data?

Royal Mail's Postcode Address File (PAF) is the definitive source of postal addresses in the United Kingdom. For most premises, there is a one-to-one relationship between a physical building and a postal address. However, many properties are subdivided into multiple self-contained units, such as flats in a converted house, student accommodation clusters, or office suites. In such cases, the Royal Mail assigns a single 'delivery point' to the main entrance, but each unit still needs to be individually identifiable for mail sorting and delivery. The Multiple Residence Data set is essentially a supplementary file that lists each of those individual units, along with a reference to the parent delivery point address.

How Is It Structured?

The data is typically provided as a simple table or flat file, where each record contains fields for the parent address's postcode and unique delivery point reference, followed by the individual unit identifier (e.g. 'Flat 1', 'Flat 2', or 'Apartment A') and sometimes a separate sub-building name. This allows the main postal address to remain unchanged while still acknowledging the existence of multiple occupancies. The data covers all types of multiple occupancy: purpose-built blocks, conversions, retirement complexes, and even temporary accommodation such as houseboats in a single mooring with a communal post box.

Where Does It Sit in the UK Postcode and Geography System?

The Multiple Residence Data is a part of the broader address infrastructure. The central building block is the Royal Mail PAF, which contains around 30 million delivery point addresses. Among those, several hundred thousand are actually multiple residence 'parents' that have one or more sub-units listed in this separate dataset. Geographically, each unit still falls within the same postcode sector and unit postcode as the parent building. The key difference is that the sub-units are not assigned their own individual delivery point reference; instead they are children of the main delivery point. This means that when you query a postcode, the PAF returns the parent address, and it is only by cross-referencing with Multiple Residence Data that you can see the full set of occupiable units. In the Ordnance Survey's address products, such as AddressBase, these sub-units are given their own Unique Property Reference Numbers (UPRNs), linking the Royal Mail data to the wider geographic framework.

How It Relates to Postcodes and Addresses Specifically

Every unit listed in Multiple Residence Data shares the same postcode as the parent building. For example, a large Victorian house converted into four flats might have the address '123 High Street, Townsville', but the four flats are recorded as 'Flat 1', 'Flat 2', 'Flat 3', and 'Flat 4' at that same address. Without the Multiple Residence Data, a researcher looking at the postcode 'AB12 3CD' would only see the single parent address and might incorrectly assume the building is a single dwelling. The data therefore provides the granularity needed to understand the true number of residential units within a postcode area. It is particularly important for distinguishing between single-family homes and multiple-occupancy buildings, which in turn affects population density estimates and service planning.

Why It Matters to Someone Researching an Area

For anyone studying demographics, housing, or local services, Multiple Residence Data is invaluable. It enables researchers to:

  • Count the actual number of households in a postcode or neighbourhood, rather than just the number of delivery points.
  • Identify blocks of flats or converted houses that may have higher densities and different tenure types.
  • Correctly allocate population estimates from census data, which often uses address counts as a base.
  • Plan for utilities, rubbish collection, and postal services at the sub-building level.
  • Understand the mix of housing types - for example, whether an area contains many converted flats or purpose-built apartments.

Without this data, analyses based solely on the PAF would systematically underestimate residential numbers in cities and towns where multiple occupancy is common. Local authorities rely on it for council tax registers and electoral rolls; emergency services use it to locate individuals in large complexes. In short, Multiple Residence Data fills a critical gap between the outward appearance of a building and the real living arrangements within it, making it a fundamental resource for accurate geodemographic research.