Is it party time when we want to extend our terrace?

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Is it party time when we want to extend our terrace?

Party Walls

Party walls or shared walls are partitions erected on a property boundary, partly on the land of one owner and partly on the land of another, to provide common support to the structures on both sides of the boundary.  Commonly found in attached and semi-detached houses, they provide the structural support from which to build upon whilst also having fire rated and sound proofing qualities.  Other examples of party structures exist in the form of high rise apartment floors and roofs.Party Wall Diagram

Ownership can take on different forms. It may mean:

  1. a wall of which the adjoining owners are tenants in common;
  2. a wall divided longitudinally into two strips, one belonging to each of the neighbouring owners;
  3. a wall which belongs entirely to one of the adjoining owners, but is subject to an easement or right in the other to have it maintained as a dividing wall between the two tenants.

What happens when a forward-thinking owner of an attached or semi-detached house wants to extend, develop or improve the current structure? How can neighbours reach agreement when neither party entirely owns the wall?

First, consent must be obtained from the adjoining owner or owners.  It is a legal requirement that all owners give consent to the lodging of the application to council. A development application cannot proceed or be granted unless all parties have written consent to allow the works.  There cannot be any conditions from adjoining owners – it is either a simple “Yes” or “No”.

There may be some benefits for the neighbour to approve or give consent to the future development or extension.  It may improve the neighbour’s wall and provide a basis upon which they can extend or duplicate the proposed works in the future, should they wish.  In any case, it may add value when it comes time to sell their property as there would now be a precedent for a future extension as well as the physical structure to build upon.

Disputes can arise if both parties can’t agree on the development, renovation or alteration of the shared wall. But if no consent is given from one or more parties this certainly doesn’t stop the proposal, it just means the method of effecting the development may need changing, which may result in a more expensive outcome.  This is the point at which some people have to assess whether the project is still feasible or whether it is time to move on and buy or build elsewhere.

Where the application does not have adjoining owners consent, but includes a design which shows that the works are to be supported independently of the party wall, these plans must be accompanied by a certificate from a qualified Structural Engineer.


The owner of No.1 demolishes the light grey shaded area and rebuilds as shaded dark grey. No. 1 is relying for vertical support on the party wall with No. 3 and therefore needs the written consent of No. 3. No. 1 will also need the written consent of No. 3 even if demolition is not proposed as the works rely on the party wall for support. Party wall demolish
The owner of No. 3 constructs an extension that relies on the party wall for support; therefore No. 3 needs the written consent of No. 1 in order to lodge the application. party wall extend
The owner of No. 1 is unable to obtain the written consent of No. 3 for works involving the party wall. No. 1 therefore must provide details from a structural engineer which identifies how the new work will be independently supported without any reliance on the party wall. The structural engineer certifies that the new works will not rely on the party wall for vertical or lateral support. Architectural plans must be amended accordingly. Party wall engineering


So, can we extend our terraced house?

Yes –  providing there is consent from the adjoining owners or consent from the body corporate if it’s on strata title.

Yes – even if consent is not given from the neighbour, providing there is supporting evidence from a structural engineer to prove the new wall can be built independent of the party wall.  This is not the ideal solution as it can become a very expensive exercise with underpinning or bored piers to support the wall.

Love thy neighbour is definitely the approach when dealing with this situation. After all, it may be mutually beneficial to both parties if the development of the party wall moves onward and upward.