Internal services


Internal services shall not adversely affect the stability of the home and be installed to ensure satisfactory operation. Issues to be taken into account include:

  1. fitting of pipes and cables
  2. notching and drilling of joists
  3. concealed services.

Fitting of pipes and cables

Services should:

  • comply with Chapter 5.1 ‘Substructure and ground-bearing floors’ where they pass through the substructure
  • be protected by a sleeve, or ducted, when passing through structural elements and not solidly embedded
  • not be located in the cavity of an external wall, except for electricity meter tails
  • not be buried in screeds unless permitted by relevant codes of practice.

Where copper pipes are permitted in floor screeds, they should be:

  • sleeved or wrapped so that they can move freely along the length and at joints and bends
  • jointed with capillary joints.

Pipes should:

  • be adequately secured with suitable clips or brackets
  • be installed neatly with clips spaced to prevent sagging, but not restrict thermal movement
  • have adequate falls (where appropriate)
  • be installed with adequate room for thermal expansion and contraction to avoid damage and noise.

Metallic tape should be placed behind plastic pipework, where it is concealed behind wall surfaces, and would otherwise not be located by a metal detector or similar equipment.

Joints in pipes should be made:

  • strictly in accordance with the manufacturer’s instructions
  • using lead-free flux recommended by the pipe manufacturer, with traces removed immediately after jointing.

Fire stopping should be provided around any services which penetrate fire-resisting floors, walls or partitions. Where a proprietary system, such as an intumescent seal is used, it should be installed in accordance with the manufacturer’s instructions.

Notching and drilling of joists

Notching, drilling and chasing to accommodate service pipes and cables should either:

  • comply with the clauses below, or
  • be designed by an engineer.

Solid timber and studs

Table 8: Limits for notching and drilling solid timber members

LocationMaximum size
Notching joists up to 250mm in depthTop edge 0.1-0.2 x span0.15 x depth of joist
Drilling joists up to 250mm in depthCentre line 0.25-0.4 x span0.25 x depth of joist
Drilling studsCentre line 0.25-0.4 x height0.25 x depth of stud

Where the structural strength is impaired by notching or drilling, the element should be replaced or correctly repaired.

Holes should be spaced at a minimum of three times the hole diameter.

Notches and holes in the same joist should be separated by a minimum horizontal distance of 100mm.

Instructions should be obtained from the designer when notching and drilling, where:

  • the joist is deeper than 250mm, or
  • the dimensions are not in accordance with Table 8, or
  • it is close to heavy loads, such as those from partitions, cisterns, cylinders and stair trimming.


Preformed holes are provided, and additional holes and notches should not be cut without the approval of the manufacturer.

Metal web joists

Services should run in the gaps between the metal webs. Conduits may need to be inserted before the joists are fixed in position.

Lightweight steel

Lightweight steel should be used in accordance with Chapter 6.10 ‘Light steel framing’.

Concealed services

Services concealed in walls or floors should be located so that significant cracking of the surface does not occur. Where chases in walls are necessary, their depth should not exceed:

  • 1/6 thickness of the single leaf for horizontal chases
  • 1/3 thickness for vertical chases.

Hollow blocks should not be chased unless specifically permitted by the manufacturer.

Pipes under floor screeds should:

  • be protected by wrapping or ducting
  • have adequate allowance for thermal expansion, particularly at changes of direction.

Screed cover should be a minimum of 25mm over pipes and insulating material, and:

  • where pipes cross, it may be necessary to form a duct to achieve adequate cover
  • for in-situ suspended concrete floors, the location and depth of pipes should be approved by the designer.