Building on the Boundary or Line of Junction

Party Wall Agreement regulations are described in the Party Wall Act. This permits you to build up to, or astride, the line of junction, or boundary with your neighbour

The correct notices must be served, and the correct process followed, as described by the Act.

Can I build up to or over the boundary line?

Yes. The Party Wall Act permits you to build up to or astride the line of junction/boundary with your neighbour, but the correct notices must be served and the correct process followed.

Steven Way, Practice Principal of Collier Stevens, says, “There is often a misunderstanding here. Without a neighbour’s agreement, there is no right to build a wall over the boundary line. The Party Wall Act DOES permit foundations to be built over the boundary, but only ’where necessary’. In my opinion, they are never necessary for domestic work and are seldom necessary for larger projects. In nearly all cases an eccentric foundation, where the wall sits on the outer edge of the foundation, can be designed. These are one of the most commonly used foundation designs in rear or side extensions and are usually preferred by Party Wall Surveyors.”

Here we answer more of your questions in detail.

What defines a boundary?

The boundary could be the boundary wall, the garden boundaries, or the boundary fence. There may not even be a specific structure there, it is simply the point at which your property joins that of an adjacent building owner. For example, a lawn may be shared across the front elevation of two semi-detached properties.

How close can I build to my neighbour’s boundary?

The party wall act allows an absolute right to build up to the property boundary between you and your neighbour. It also allows you to build astride the boundary line, but only with your neighbour’s consent.  

Is a fence a party wall?

Whilst a fence is clearly not a wall, within the party wall act a boundary wall built on the boundary line is referred to as a party fence wall.  The Party Wall Act does not deal with fences.

Can a neighbour use my wall? Can I use my neighbour’s wall?

This question often arises when people want to build side extensions. Side extension rules are the same as any other boundary. The wall can only be used if it is an existing party wall or party fence wall – that means the boundary line must run through it. If a wall is wholly on your neighbour’s side, there is no right to use it granted by the Party Wall Act, but there is a right to cut a flashing into it.

Can I build on my neighbour’s land?

There is no right to build on your neighbour’s land except to place foundations for a new wall. The act permits footings to be placed on next door’s land only ‘where necessary’. In nearly all cases an eccentric foundation, where the wall sits on the outer edge of the foundation, can be designed which means that no foundation needs to project into next door’s plot.

What is the process for building on the boundary?

If you want to build a wall or garden wall astride the boundary line (called the ‘Line of Junction’ in the Party Wall Act), you must tell your neighbour by serving a notice, called a Party Wall Notice. If you want to build a wall astride the boundary line, it will be as a party wall, and you can only do this with your neighbour’s written approval. You must also inform the adjoining owner if you plan to build a wall wholly on your own land but up against the boundary line, but in this case, your neighbour cannot prevent you from building such a wall.

The Act sets out the precise information you must tell your neighbour, and this must be in writing. There is a standard Party Wall Notice to make sure that this is done correctly, and we’ve uploaded templates to help you. The correct template to complete is a “Section One” notice. Alternatively, you may feel happier appointing a party wall surveyor to do this for you. Collier Stevens has a competitive fixed fee service which includes serving the correct notices.

There is no right to build astride the boundary, and if your neighbour objects, then you might have to alter your drawings, so it is best to check early on.

What if I want to build next to the boundary, but on my land?

If you build on your land away from the boundary (even by a small amount), you will not need to notify your neighbour. However, if you are forming foundations, you may need serve a notice under Section 6 of the Party Wall Act, if their building is closer than 3m. See also “Excavating Near Your Neighbour”.

My neighbour’s wall is on the boundary. Can I build against it?

Yes, there is no restriction on this, but you will almost certainly need to serve a notice for adjacent excavation. If you find the foundations are over your side, you will need to serve a party wall notice to cut these away, and you may have to underpin their wall at your cost.

When do I need to serve a notice if I want to build on or astride the line of junction (boundary)?

At least one month before the planned starting date for building the wall.

What happens after I serve a notice to build astride the boundary line?

The adjoining owner has 14 days to agree in writing to the building of a new party wall astride the boundary line. If they do this, the work may go ahead. 

If the adjoining owner does not respond or objects to the proposed new wall astride the boundary line, you must build the wall wholly on your own land, and wholly at your own expense.

What if my neighbour moves before we complete work and the new neighbour objects?

If you have reached party wall agreement and your neighbour moves out, the agreement has still been made. It cannot be rescinded by your new neighbour as it will have been included within the sale of the property.

Can I ask my neighbour to pay towards the costs of building a party wall?

No. But because the wall is shared, if your neighbour wants to use it later on, perhaps as a part of their extension, the Act says that they will need to pay you compensation. This is usually (but not always) half the cost of that part of the wall, including its foundations, that has been used.

What happens after I serve a notice to build up to, but not over, the boundary line?

You may start work one month after you serve your notice. This work may include footings and foundations that extend under the adjoining owner’s land.

The wall will be built wholly at your own expense, and you will have to compensate any adjoining owner for any damage to his property, garden or plants caused by the building of the wall or the placing of footings and foundations.

What happens if I cannot agree with my neighbour?

If there is a disagreement about any work on a boundary line, including compensation, then Party Wall Surveyors should be appointed, and the boundary dispute settled using the resolution procedures in the Party Wall etc Act. This usually means that a Party Wall Award is agreed upon. For more details about disputes, see ‘Resolving Disputes.

Is a garden wall a party wall?

Only if the boundary line runs through it. If it does, it is known as a party fence wall and can be used by either neighbour. If the wall is all on one side or the other, it is not a party wall, and it can only be used by the neighbour who owns it.