OK, here it is, from the same BS:
8.8 Pipes buried in concrete ground floors
8.8.1 Installation pipework shall not be buried in concrete slabs.
8.8.2 Rigid stainless steel pipework shall not be buried in concrete screeds.
Pipe buried in concrete screed shall be installed in accordance with Figure 5.
Where a pipe is buried in a concrete screed there shall be a minimum of 25 mm of cover above the pipe.
8.8.3 Pipes buried in concrete ground floors shall be protected against failure caused by movement. Joints shall be kept to a minimum. Compression fittings shall not be buried in concrete screeds or concrete slab.
COMMENTARY AND RECOMMENDATIONS ON 8.8.3
Suitable methods of protection are as follows.
a) Pipe laid on top of base concrete and subsequently covered by a screed (see also 9.2.1).
b) Steel or copper pipe installed into preformed ducts with protective covers.
c) Steel or copper pipe fitted with additional soft, non-permeable covering material. The coverings should
be soft and thick enough to provide movement yet resilient enough to support the concrete cover while it is setting.
The covering should be at least 5 mm thick and resistant to concrete ingress which would negate its ability to allow movement.
Reference should also be made to 9.2.1 for the application of adequate corrosion protection.
And
8.7 Pipes laid in joisted floors
NOTE See foreword.
8.7.1 Where pipes are installed between solid timber joists in floors, intermediate floors or roof spaces, they shall be correctly supported (see Table 2).
8.7.2 Where pipes are installed between timber engineered (I) joists, the pipes shall be installed through
the web of joists in accordance with Table 2 and the joist manufacturer’s guidance.
8.7.3 Where pipes are installed between metal web joists the pipes shall pass between the metal webs with pipe supports fixed to the top or bottom of the timber flanges.
8.7.4 The flanges of timber engineered joists and metal web joists shall not be notched.
8.7.5 Where pipes are laid across solid timber joists fitted with flooring they shall be located in purposemade notches or circular holes.
Joists less than 100 mm shall not be notched. Notches shall be in accordance with Figure 4.
COMMENTARY AND RECOMMENDATIONS ON 8.7
Prior to running pipework below suspended floors a visual inspection should be carried out to note the position of any electrical cables, junction boxes and ancillary equipment, in order that accidental damage or injury does not occur when inserting pipework.
Care should be taken when re-fixing flooring to prevent damage to the pipes by nails or screws. Where possible, the flooring should be appropriately marked to warn others. Where possible the design should remove the need for notching solid timber joists.