Boundary Walls

Jon Maynard Boundaries Ltd, Boundary Demarcation and Disputes, Rights of Way, Expert Witness, Chartered Land Surveyor


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Walls and boundaries

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Party Walls
Boundary Walls
Retaining Walls
Building faces

In the context of boundaries we need to consider four kinds of wall:

  • Party wall: i.e. a wall within a building that joins two properties and forms the boundary between them;
  • Boundary wall, within a garden, so placed as to separate two parcels of land in different ownership;
  • Retaining wall: a wall supporting land that is higher on one side of the wall than it is on the other side, where that retaining wall also serves as a boundary wall;
  • Building faces: a boundary may run along the side (or front or rear) face of a building.


Party Walls

According to Section 38 of the Law of Property Act 1925 if

"a wall or other structure is or is expressed to be made a party wall or structure, that structure shall be and remain severed vertically as between the respective owners, and the owner of each part shall have such rights to support and user over the rest of the structure".

This website does not offer advice on party walls in relation to any building work on your property (e.g. extensions, damp proofing works, structural alterations) nor on how to comply with the Party Wall etc Act 1996. Such advice is the province of a chartered building surveyor. If you want such advice then you should telephone the
RICS Party walls helpline
t +44 (0)870 333 1600
which promises to put you in touch with an experienced, local RICS member who will provide you with up to 30 minutes free advice.

What this website does offer is advice on locating the position of a boundary within a party wall, and of transferring the centre of a party wall out into the garden in those cases where the title deeds show the boundary as a straight line running along the party wall and on in a straight line through the front and rear gardens.


With terraced and with semi-detached houses it is reasonably safe to assume that the boundary between the houses runs along the centre of the party wall. At left is an example of a party wall running along the centre of a cavity wall. Also, all of the chimneys are located to the same side of the boundary as the house that they serve.

If the chimneys have some other arrangement, such as in the example at right, then it is best to ask a chartered building surveyor (who will understand the structure of the building better than any other type of boundary demarcation surveyor) exactly where the boundary runs.
There are examples where the boundary runs along one side, rather than along the centre, of the party wall. This is more common in city centres and arises when a building is built right up to the boundary line and a second building is butted against it some years after the original building was constructed, as in the example below.
It is necessary to exercise care when transferring the location of the centre of the party wall from the interior to the exterior face of the building.

On one Georigian terrace (see below) I encountered protruding masonry apparently marking the positions of respective party walls. The exterior decorations (paint) of each house within the terrace were certainly applied as far as the centre of the protruding masonry on each side. When two neighbours fell out with each other, it soon became clear that the garden fences did not align with apparent boundaries observed by the external paintwork. Careful investigation showed that the fences were aligned to the actual boundary rather than to the apparent boundary.
Occasionally, the position of the centre of the party wall is readily apparent on the exterior of a building. The party wall projects through the roof of this terraced house (left), and can also be seen on the first floor front elevation where its front end is used as external decoration. More often, it is necessary to carefully measure its position as demonstrated in the drawing below.
If you have access to both properties, then measure along the inner face of the exterior wall, from both sides, the distance between the nearest door or window aperture and the party wall. Then re-measure these distances from the same apertures but along the external face of the same exterior wall. Place two marks on the outside of the building to represent the two faces of the internal party wall. The boundary is midway between these marks.

With access to only one property you can mark on the outside the position of only one face of the internal party wall and must make an allowance for half of the width of the internal party wall in order to mark the position of the boundary on the exterior of the building.

Marking onto the exterior wall the position of the centre of the party wall
If the boundary is shown on the conveyance plan (or transfer plan) as one straight line that runs between the rear gardens, along the party wall, and between the front gardens, then it may be necessary to to set out a line perpendicular to the face of the building in order to establish the position of the boundary between the gardens. To do this you will need to construct a right angled triangle using the face of the building as one of its sides. This can easily be achieved using a tape measure and a knowledge of Pythagoras' Theorem. If you need reminding of Pythagoras then visit Wikipedia.


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Boundary Walls

A wall that is used to separate two parcels of land may wholly belong to the owner of one of the parcels of land and be built entirely upon that owner's land. If it stands upon (or rather, astride) the boundary, then it will be jointly owned by both landowners and might be referred to as a "party wall". To differentiate between a party wall separating the gardens of two properties and a party wall joining two houses together, the Party Wall etc. Act 1996 has coined the term “party fence wall” for a wall that stands in the garden:

“party fence wall” means a wall (not being part of a building) which stands on lands of different owners and is used or constructed to be used for separating such adjoining lands, but does not include a wall constructed on the land of one owner the artificially formed support of which projects into the land of another owner;

The Party Wall, etc Act 1996 differentiates between a “party fence wall” and a “boundary wall” that is placed wholly on the land of one owner. A "boundary wall" is thus:

a wall constructed on the land of one owner

A party fence wall is therefore a wall that stands astride a boundary, and the boundary will normally run along the centre line of the wall.

Most free standing walls are supported by piers - towers of bricks attached to the side of the wall to provide additioNAl strength. A boundary wall will normally be built with all of its piers on one side only of the wall, so as to keep the whole of the wall on its owner's land. A party fence wall may have its piers protruding from both sides of the wall. However, Section 1 (6) of the Party Wall, etc Act 1996 does allow for the supports of a boundary wall to be placed below the level of the land of the adjoining owner.

Documentary evidence for the position of the boundary:
Sometimes the conveyance plan or transfer plan will make the ownership of a wall clear by the use of T-marks for a boundary wall or H-marks for a party fence wall (see Fences for an explanation of T-marks and H-marks). Sometimes it will be stated in the wording of the deed. In the absence of such an indication it becomes necessary to examine the physical evidence in order to establish the position of the boundary in relation to the wall.

Physical evidence for the position of the boundary

Identifying the position of the boundary in relation to a boundary wall is not as straightforward as it seems. The diagram at left suggests three possible positions for the boundary. Fortunately, the Party Wall, etc Act 1996 clarifies the situation:
(6)  Where the building owner builds a wall wholly on his own land in accordance with subsection (4) or (5) he shall have the right .....
..... to place below the level of the land of the adjoining owner such projecting footings and foundations as are necessary for the construction of the wall.
So the boundary follows the face of the boundary wall and the footings are permitted to lie under the neighbour's land. Presumably, the overhang of the capping is similarly permitted and does not present grounds for a claim of encroachment.


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Retaining Walls

Retaining walls occur where there is a change of ground level between the land on either side of the wall. A retaining wall must have greater strength than a normal wall in order to support the weight of the land retained on the higher side of the wall. The requirement for this extra strength makes them more expensive to build and more expensive to repair.

Problems can arise when a retaining wall is located on a boundary. There are two circumstances to consider:

  • a landowner who owns a retaining wall that supports his neighbour's higher land is subject to an implied (unless it is expressly stated in a deed) easement and owes a duty of support to his neighbour's land;
  • a landowner who owns a retaining wall that supports his own land is under a general duty of care to maintain the wall in such a condition that his land is prevented from collapsing onto his neighbour's lower land.

It is usually when a retaining wall (on a boundary) falls into disrepair that its ownership comes into question. Neither landowner wants to go to the expense of repairing the wall and each sees an opportunity to force his neighbour to undertake the work. The situation should not arise if the deeds of one or both properties are specific as to ownership of the retaining wall. It is when the deeds are silent that an investigation of the position of the boundary is needed.

An investigation can only succeed if the deeds contain a particularly clear and accurate description of the boundaries. Often the deed and plan are so imprecise that it is possible to determine the position of the boundary to only a decimetre (100 mm). This may be enough to ascertain that the wall is on the boundary but insufficient to ascertain on which side of the boundary its stands.


Building faces

It sometimes happens that a house or other building is built right up against the boundary of the land on which it stands. In these cases the boundary usually runs along the outer face of the external wall of the building. The eaves may project above the neighbouring land, and the footings may project beneath the neighbouring land. Such eaves and footings will be considered as part of building to which they are attached, but the airspace between them will belong to the adjoining land.


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