20.Section 4 makes provision about the meaning of “independent part”.
21.If a part of a structure or set of structures is an “independent part” (“Part A”) then that part is a “building” for the purposes of section 2 (see section 3(5)). If Part A meets the criteria for being a regulated building, then, depending on what category of building it is, the relevant duties under the Act apply in respect of it. For example, if Part A is a category 1 or category 2 building, the principal accountable person commits an offence if Part A is “occupied” but not registered (section 19). “Occupied” is defined in section 136.
22.The intention behind the independent part test is to recognise that if a part of a structure or set of structures meets certain criteria it is appropriate for it to be considered a “building” in its own right (rather than the whole of the structure or set of structures being considered a “building” and the “regulated building” test being applied to that whole).
23.The “independent part” criteria look at whether a part has access to other parts of the structure (or set of structures) and whether it overhangs other parts that are residential. If an independent part, then meets the criteria for being a “regulated building”, most of the duties under the Act apply by reference to the parameters of that independent part and any ancillary areas that it may have (see section 7). An example is the duty under section 29 for the principal accountable person for an “occupied” regulated building to ensure that there is an assessment of the fire safety risks relating to that building.
24.The criteria for being an independent part are set out in subsection (1). There are two elements to the criteria (paragraphs (a) and (b)) and both elements must be met.
25.Paragraph (a) requires the part being considered to have no “access” to another part of the structure (or set of structures, if it is part of a set of structures). If there is “access” from one area of a structure to another then neither of those areas is individually capable of being an “independent part” (unless the “access” is disregarded under subsection (7) e.g. if it is intended to be for emergency use only).
26.Paragraph (b) requires the part being considered to constitute a vertical division of the structure or set.
27.Subsection (2) sets out the meaning of vertical division. It provides that for the part being considered to constitute a “vertical division” that part must divide the structure (or set of structures) from the top to the bottom, and the line/ lines of the division must not deviate from a vertical plane. However, this is subject to subsection (3).
28.The effect of the vertical division element of the independent part criteria is to prevent a part of a structure that contains a residential unit and that overhangs a part of a structure containing another residential unit, from constituting a separate building under the Act, even where the two parts have no access to each other. One of the reasons for this is to recognise that if fire spreads it is most likely to spread upwards. Therefore, for example, in the scenario described here the overhanging part and the underhanging part would be considered a single building and risk assessment duties under the Act would apply accordingly.
29.Subsection (3) provides that when applying the “vertical division” test to a part, the existence of any other parts of the structure (or set of structures) that meet the criteria in that subsection are to be disregarded so that they do not prevent the vertical division test from being met.
30.If one was trying to visualise the effect of subsection (3), one could visualise the potential independent part (“Part A”) of a structure as being shaded in a particular colour, and the part that meets the criteria in subsection (3) (“Part B”) being shaded in the same colour, so that the two parts together form a block of one colour. The two parts would together form a block of one colour that divides the structure from top to bottom along a vertical plane. Part A would be an independent part, provided it also met the criteria in subsection (1)(a) – no access to any other part of the structure.
31.Subsection (4) defines “non-residential part” for the purposes of subsection (3).
32.An example to consider is a scenario in which there are two blocks of flats above a commercial premises, no part of either block overhangs the other block, and they do not share access with each other or with the commercial premises. The effect of subsection (3) would be that the existence of the commercial premises would not prevent each block from constituting a vertical division of the structure. Assuming that each block has an entrance area (e.g. stairwell or access to lifts) that runs adjacent to (but does not share access with or have access to) the commercial premises at the ground floor level, then there will inevitably be some deviation in the line of the vertical division as between the commercial premises and the block above. However, thinking of the scenario in visual terms, the effect of subsection (3) is to shade the part of the commercial area that is under each block in the same colour as the block so that each block is treated as if it divided the structure from top to bottom along a vertical plane. In such a scenario each block of flats would be an “independent part” and therefore a “building” for the purposes of section 2.
33.Subsection (5) makes provision for cases where a part of a building would meet the vertical division test but for the fact that the part cannot constitute a “vertical division” of the structure because the part makes up the whole width of the structure. For example, where there is a single block of flats above commercial premises the block of flats is still capable of being an “independent part” (and therefore a “building”) separate from the commercial part below (so long as it does not share access with or have access to the commercial part). The reason for this provision is to achieve a result in this type of scenario that is consistent with the result in the scenario described above (two blocks of flats above commercial premises).
34.In the scenario of two blocks of flats, each block of flats emerges from the independent part test as a separate independent part, and therefore, “building”. The commercial premises is not part of either “building” under the Act (although there are duties imposed by the Act that would relate to the commercial premises). Subsection (5) is for the purpose of achieving a consistent result in the scenario of a single block of flats above commercial premises (with which the block does not share access, and to which it does not have access) – the block of flats would emerge from the independent part test as an independent part and therefore “building” under the Act. The commercial premises would not be part of that building.
35.Subsection (6) enables the Welsh Ministers to make regulations to specify that, in particular circumstances, a part of an unattached structure or set of structures is an “independent part,” despite it not being such under this section. This enables more unusual ownership models and designs of buildings to be accommodated, so that the duties under the Act apply appropriately.
36.Subsection (7) defines “access” as being a doorway, archway or similar opening. Such accesses intended for exceptional use (such as emergency use) or use for the purposes of maintenance are not included.
Commentary on Sections Part 1 - Safety of Buildings Containing Two Or More Residential Units Regulated buildings, residential units and categories of building Section 4 - Meaning of “independent part”