Home Practice Notes on Underpinning

Practice Notes on Underpinning



  • A solid foundation made below ground level to support or strengthen a building.
  • Material or masonry used to support a structure such as a wall. 
  • A support or foundation.
  • Support, base, foundation, footing, groundwork.
  • A strong piece of metal or concrete that supports something such as a wall
  • A solid foundation laid below ground level to support or strengthen a building.



  • To set upright.
  • To make to stand up
  • To set a thing on end
  • To build up, construct, create, produce etc
  • To lift up and put in position the parts of a structure
  • To construct by piling up, building or fitting together
  • To found, build up


Common Law

  • An owner has the right subject to statute and not causing nuisance to his neighbours to excavate his own land.  He must maintain the land of his neighbour.  His land will extend in the case of party walls to (normally) half the thickness of the wall.  The implication is that an owner has always had a right to form a basement with the support of the neighbour’s land being entirely on the developer’s land (including half a party wall) (normally).
  • It does not matter whether the work under the party wall is defined as being a ‘downward raising’ or underpinning.  It is a retaining structure in the nature of a wall.
  • The downside of this argument is that all loads imposed by the party wall have to be taken on the developer’s new structure and before the LBA’s that means the future developer would have been in difficulties if he wished to mirror the exercise.


  • ACT:  “In relation to a wall means the solid ground or artificially formed support resting on solid ground on which the wall rests.”
  • OED:  The lowest load-bearing part of a building typically below ground level.

Forming a Basement Wall

  • Underpinning, raising a wall downwards or both?
  • 2 (2) (a) gives a right to underpin the whole width of a party wall.
  • Underpin is defined as “a solid foundation below ground level to support or strengthen a building”.  Depth of underpinning is not defined in the Act and could not be for practical reasons.  Underpinning suggests a foundation whereas the concept of raising a wall downwards implies that the retaining element of the downward raising is a wall rather than a foundation and may therefore be reinforced without the need for an Adjoining Owner’s consent.
  • One definition of underpin – “a support” or a “foundation” could reasonably include a wall.
  • Since a wall is not a foundation, consent for reinforcement would not be required.  The difficulty arises where the wall meets the foundation.

    Special Foundation

    • Consent for special foundations is required when in modern construction steel rods are placed in concrete as reinforcement to distribute loads and such reinforcement is to be placed on the land of the Adjoining Owner.

    Where are the lines drawn?

    • The simplest answer is to cast a reinforced concrete wall on a mass concrete foundation in exactly the same way as walls and foundations are built normally, however, this poses some practical difficulties of construction and was originally rejected by a High Court Judge in a Moot.  Subsequently and with owners with much to lose this issue was decided in the County Court of Central London Technology and Construction List by his Honour Judge Edward Bailey as being an acceptable method of construction not requiring the Adjoining Owner’s specific consent for Special Foundations.
    • The most common proposal is the reinforced concrete box, a wall of which supports the party wall.  The vertical reinforcing bars in the wall element are bent 90º to reinforce the floor slab.  This solution falls under the definition of foundation and being reinforced, a special foundation, for which the Adjoining Owner’s consent is required.

    Is the retaining wall a special foundation requiring consent if it is only reinforced on the Building Owner’s side of the boundary?

    • This effectively implies the construction of a wall with two elements, one reinforced the other mass concrete.  The vertical load from the party wall would be carried by the entire wall into the foundation on both parties land.  As such since the steel in the wall is on the Building Owner’s side of the Line of Junction and not on the Adjoining Owner’s side it is not a special foundation.
    • The alternative view is that it does not matter where in the wall reinforcement is placed.
    • The wall is reinforced and thus the Adjoining Owner’s consent for special foundations is required.
    • It remains to be seen if the argument that reinforcement on the Building Owner’s side only to restrain lateral movement does not distribute load from the party wall.

    Why are we here?

    • Over the last few years the debates on the form of basement construction have intensified the reason for which being a substantial increase in owners seeking to expand their living space in expensive areas of London and it could be argued the failure of Surveyors to find common ground on the interpretation of the Act is increasing the costs of Building Owners.
    • The various definitions of ‘raise’ suggests, contrary to the view expressed by Akenhead, that a wall could be increased in height by building downwards, reinforced concrete without the need for consent bearing on mass concrete (the foundation).
    • Underpinning is defined as a foundation therefore, if notice is served to underpin the wall element and base containing steel reinforcement, it would be special and subject to the Adjoining Owner’s consent.
    • In the design of the underpin the Adjoining Owner must not be disadvantaged from carrying out similar work themselves and thus the loads must not be carried entirely onto the Building Owner’s land.  
    • If that consent is not forthcoming then the Building Owner now has the option of reverting to founding his reinforced concrete box on a mass concrete foundation.


    1. Section 4 (1) (b) when consent under 7 (4) given then Adjoining Owner may give Counter Notice for the special foundations be constructed of sufficient strength to bear the load of columns of any intended building of the adjoining owner.
    2. Should an Adjoining Owner give consent to special foundations then care has to be taken to ensure that during the course of the work the concrete is cast up to the agreed vertical planes and not encroaching upon the Adjoining Owner’s land beyond the limit set by the party wall surveyors.
    3. For general guidance see attached Practice Notes. 

    Party Wall Articles/Underpinning