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Class B: Development by or on behalf of sewerage undertakers
Class B covers specified development by or on behalf of a sewerage undertaker. Underground sewer and outfall works, surveys, flow measurement, pumping-system equipment and some operational-land work have separate limbs.
The Class is limited by the type, location and size of the work; it is not a general permission for a new treatment-works building.
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Permitted development can avoid a full planning application, but only if the right applies and every relevant limit and condition is met. Planning Geek can check the planning history, Article 4 directions and other restrictions, and help with a lawful development certificate or prior approval where needed.
Main limits and conditions
B(d)’s 29 m³ threshold restricts a station or house at or above ground level or under a vehicular highway. B(f) permits some works on operational land but excludes a new building; alterations to an existing building and tall plant have further limits. B.3 defines associated apparatus and a sludge main.
A B(b) survey must end at completion or within six months of starting, whichever is sooner. Remove temporary equipment and restore the land as soon as reasonably practicable. Check Part 13, Class B and the general limits.
Legislation
Class B – development by or on behalf of sewerage undertakers
Permitted development
B. Development by or on behalf of a sewerage undertaker consisting of—
(a) development not above ground level required in connection with the provision, improvement, maintenance or repair of a sewer, outfall pipe, sludge main or associated apparatus;
(b) the provision of a building, plant, machinery or apparatus in, on, over or under land for the purpose of survey or investigation;
(c) the maintenance, improvement or repair of works for measuring the flow in any watercourse or channel;
(d) the installation in a sewerage system of a pumping station, valve house, control panel house or switch-gear house;
(e) any works authorised by or required in connection with an order made under section 73 of the Water Resources Act 1991 (power to make ordinary and emergency drought orders);
(f) any other development in, on, over or under their operational land, other than the provision of a building but including the extension or alteration of a building.
Development not permitted
B.1 Development is not permitted by Class B if—
(a) in the case of any Class B(d) development involving the installation of a station or house exceeding 29 cubic metres in capacity, that installation is carried out at or above ground level or under a highway used by vehicular traffic;
(b) in the case of Class B(f) development, it would consist of or include the extension or alteration of a building so that—
(i) its design or external appearance would be materially affected;
(ii) the height of the original building would be exceeded, or the cubic content of the original building would be exceeded, by more than 25%; or
(iii) the floor space of the original building would be exceeded by more than 1,000 square metres; or
(c) in the case of Class B(f) development, it would consist of the installation or erection of any plant or machinery exceeding 15 metres in height or the height of anything it replaces, whichever is the greater.
Condition
B.2 Development is permitted by Class B(b) subject to the condition that, on completion of the survey or investigation, or at the expiration of 6 months from the commencement of the development concerned, whichever is the sooner, all such operations cease and all such buildings, plant, machinery and apparatus are removed and the land restored as soon as reasonably practicable to its former condition (or to any other condition which may be agreed with the local planning authority).
Interpretation of Class B
B.3 For the purposes of Class B—
“associated apparatus”, in relation to any sewer, main or pipe, means pumps, machinery or apparatus associated with the relevant sewer, main or pipe; and
“sludge main” means a pipe or system of pipes (together with any pumps or other machinery or apparatus associated with it) for the conveyance of the residue of water or sewage treated in a water or sewage treatment works as the case may be, including final effluent or the products of the dewatering or incineration of such residue, or partly for any of those purposes and partly for the conveyance of
trade effluent or its residue.
Page updated: 24th September 2026