Garden walls and boundary walls: when the Act applies

Garden walls generate a surprising amount of party wall work. They are often old, leaning or cracked, they are frequently built across the boundary, and they are affected by extensions, garages and garden rooms built alongside them. The key is identifying what kind of wall you have, because that decides which part of the Act applies.

Identify the wall first

The Act defines a party fence wall as “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”, excluding a wall built on one owner’s land whose footings merely project into the other’s (section 20). Title plans rarely show the exact boundary position, so in practice a surveyor looks at the wall, its footings, any piers and the plans, and the two owners usually agree where the line of junction is.

Work to an existing party fence wall

The section 2 rights most often used on garden walls are:

• Raising or underpinning the wall (s.2(2)(a)), for example to make it higher for privacy or to support it.
• Repairing, or demolishing and rebuilding it where this is necessary because of defect or want of repair (s.2(2)(b)). Costs are then shared in proportion to use and responsibility for the defect (section 11(5)).
• Raising the wall, raising it for use as a party wall, or demolishing and rebuilding it as a party fence wall or party wall (s.2(2)(l)). This is the usual route when you build an extension or garage on the line of an old garden wall.
• Reducing its height to not less than two metres where the neighbour uses it only as a boundary wall (s.2(2)(m)). The neighbour can serve a counter notice requiring the existing height to be kept, paying a due proportion of the cost of the excess (s.11(7)).
• Cutting into it for a beam, flashing or other purpose (s.2(2)(f)), or cutting away projecting footings (s.2(2)(g)).

All of these need a party structure notice under section 3 at least two months before work, and the neighbour has 14 days to consent before a dispute is deemed (section 5).

Building a new wall on the boundary

Where the land at the boundary is not built on, or has only a boundary wall that is not a party fence wall, section 1 applies. You have two choices:

• A wall astride the line as a party wall or party fence wall. Serve notice at least one month before (s.1(2)). If the neighbour consents within 14 days, the wall is built half on each owner’s land (or as agreed) and costs are shared according to use (s.1(3)). If they do not consent, you may only build it wholly on your own land at your own expense (s.1(4)).
• A wall wholly on your own land up to the line. Serve one month’s notice (s.1(5)). You may then place projecting footings and foundations under the neighbour’s land where necessary, within the window starting one month and ending twelve months after service (s.1(6)), at your own expense and compensating for any damage (s.1(7)). Reinforced (special) foundations still need written consent (s.7(4)).

See section 1: building a new wall on the boundary for the detail.

Excavation near garden walls

Section 6 applies to excavation near a “building or structure” of the neighbour. Surveyors generally treat a substantial masonry garden wall as a structure, so digging foundations for an extension within 3 m and below the wall’s footings can need a section 6 notice even where the wall itself is untouched. Ask your surveyor to check the depths.

What surveyors look for

• Whether the wall is astride the line, wholly on one side, or has a footing projecting across.
• Its condition: leaning, bulging, cracked, frost-damaged brickwork, missing copings, tree root damage. Old garden walls are often in poor condition before any work starts, so a Schedule of Condition is valuable.
• Whether retained earth is involved. A garden wall holding back higher ground on one side is acting as a retaining wall and needs engineering care.
• Planting, sheds and fixtures on the neighbour’s side that need protecting or moving, and how access will be gained (section 8).
• Height: planning rules limit boundary wall heights without permission. Check with your planning authority.

Common problems

• Treating a party fence wall as “ours”. Even if you have always maintained it, it may be astride the boundary.
• Demolishing an old garden wall without notice to build an extension. Rebuilding a party fence wall as a party wall is section 2(2)(l) work.
• Disputes about the boundary line. The Act does not decide boundary disputes; surveyors work from what the owners agree or what is evident. A genuine boundary dispute may need separate advice.
• Cost-sharing arguments over a defective wall. These are settled under sections 11(4) and 11(5) by the surveyors if the owners cannot agree.

Checklist

• Establish the wall type and where the line of junction runs.
• Decide which section applies: 1, 2/3 or 6, or more than one.
• Serve notices on all owners, including any owner of a garden behind.
• Record the wall’s condition beforehand.
• If the wall is defective, raise cost-sharing early.

Worked example (illustrative)

Illustrative only. Not a real case.

A homeowner wants a single-storey side extension along the line of an old 1.8 m brick wall shared with the neighbour’s garden. The wall stands astride the boundary, so it is a party fence wall. The plan is to demolish it and rebuild it as the flank wall of the extension, which is section 2(2)(l), and the new foundations will be dug within 3 m of the neighbour’s garage, below its footings, which is section 6. A section 3 notice and a section 6 notice are served together, with drawings. The neighbour consents but asks for a Schedule of Condition of their garage. The wall is rebuilt as a party wall; because the neighbour does not use the new building element, they pay nothing, and if they later enclose on it, section 11(11) allows a contribution to be claimed at that time.

Costs with us

Domestic extensions and loft conversions. Fixed fees, invoiced on completion; we take enquiries only, with no online payment. If your neighbour appoints their own surveyor, the building owner normally pays that surveyor’s reasonable fees as well (s.10(13)), and those are set by that surveyor, not by us.

Sources and further reading

• Party Wall etc. Act 1996, section 1: New building on line of junction (legislation.gov.uk)
• Party Wall etc. Act 1996, section 2: Repair etc. of party wall: rights of owner (legislation.gov.uk)
• Party Wall etc. Act 1996, section 3: Party structure notices (legislation.gov.uk)
• Party Wall etc. Act 1996, section 5: Disputes arising under sections 3 and 4 (legislation.gov.uk)
• Party Wall etc. Act 1996, section 6: Adjacent excavation and construction (legislation.gov.uk)
• Party Wall etc. Act 1996, section 7: Compensation etc. (legislation.gov.uk)
• Party Wall etc. Act 1996, section 8: Rights of entry (legislation.gov.uk)
• Party Wall etc. Act 1996, section 11: Expenses (legislation.gov.uk)
• Party Wall etc. Act 1996, section 20: Interpretation (legislation.gov.uk)
• The Party Wall etc. Act 1996: explanatory booklet (GOV.UK)

This guide is general information on the law in England and Wales, written from our surveyors’ practical experience. It is not legal advice; for a specific dispute, take advice on your own facts.

Sources: Party Wall etc. Act 1996 (legislation.gov.uk) · The Party Wall etc. Act 1996: explanatory booklet (GOV.UK). Last reviewed 27 October 2026. General guidance on the law in England and Wales, not legal advice.