This topic refers to the potential impact on building stability from the installation of services within walls. Approved Document A, Structure, 2004 Edition, as amended, (ADA) can be downloaded from the Communities and Local Government website at www.planningportal.gov.uk
Service installations
The installation of electrical, gas, water or other services in the walls of a building is generally permitted by the Building Regulations 2010. However, removal of material from a wall for the installation of services can weaken the wall and may lead to structural movement of the wall and/or building. Therefore, the designer and installer of building services must take account of the requirement not to impair the stability of the walls where such services are to be installed within a wall.
Chases in walls
To reduce the risk of structural movement of a wall and/or building, chases in walls for the installation of services should not be positioned in such a way as to impair the stability of the wall. Furthermore, ADA recommends for particular walls that the dimensions of chases are restricted. The restrictions given in paragraph 2C30 of ADA are illustrated in Fig 1. They apply to walls constructed of masonry units, such as bricks or blocks, forming part of a residential building of up to three storeys, where such walls are parapet1 or extend to the full storey height and the walls are:
- external walls,
- internal load-bearing walls,
- compartment walls, or
- separating walls
The restrictions on dimensions of chases apply equally to parapet walls, external and internal load-bearing walls that extend to the full storey height, where such walls form part of:
- small single-storey non-residential buildings, or
- small buildings forming annexes to residential buildings (including garages and outbuildings
Where electrical equipment is installed within walls, in addition to the recommendations of ADA, the applicable requirements of BS 7671 will have to be met. In such circumstances, Regulation 527.1.2 requires a wiring system to be installed so that the general building structural performance and fire safety are not reduced.
Where a cable is installed at a depth of less than 50 mm, the requirements of Regulation Group 522.6 apply.
Rules for protection of cables against penetration
Cables embedded in a wall or partition can be vulnerable to penetration by nails, screws and the like, which can lead to the dangers of electric shock or fire. It is therefore important that cable runs are properly planned and that the cables are installed in such a manner as to afford compliance with the requirements of BS 7671. Regulation 522.6.202 requires that where a cable is concealed in a wall or partition at a depth of less than 50 mm from any surface of the wall or partition, the cable must:
(i) be installed in a zone within 150 mm from the top of the wall or partition or within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switchgear, the cable may be installed in a zone either horizontally or vertically to the point, accessory or switchgear on the surface of the wall or partition, to which the cable is connected. Where the location of the accessory, point or switchgear can be determined from the reverse side, a zone formed on one side of a wall or partition of 100 mm thickness or less extends to the reverse side, or
(ii) comply with Regulation 522.6.204.
Generally, a zone created on one side of a wall or partition does not extend to the reverse side. There is only one exception. If the location of the accessory, point or switchgear can be determined from the reverse side, a zone formed on one side of a wall or partition of 100 mm thickness or less extends to the reverse side as shown in Fig 3.
Additional protection by means of an RCD
In installations not intended to be under the supervision of a skilled or instructed person, for example, in domestic premises, cables concealed in walls and partitions are required to be provided with additional protection by an RCD unless they are protected by other specified means. The requirements are set out in Regulations 522.6.202 and 522.6.203 and are summarised below. As is always the case for additional protection, the RCD must have a residual operating current (I∆n) not exceeding 30 mA and an operating time not exceeding 40 ms at a residual current of 5I∆n.
For more information please visit: www.elecsa.co.uk
