Section 20 is the glossary of the Party Wall Act. It’s where the Act tells you exactly what it means by “owner”, “party wall”, “party fence wall”, “special foundations” and more. Getting these definitions right is crucial—because whether your works are notifiable, who must be served notice, and what rights follow all hinge on the wording in Section 20.
Below is a plain-English tour of the most important terms, with quick examples to make them stick.
Core people
Owner
Not just the freeholder. It includes anyone with an interest greater than a yearly tenancy (e.g., long leaseholders) and anyone entitled to receive the rents. There can be several owners for one address (freeholder + long leaseholder).
Why it matters: You must serve notice on all adjoining owners—missing one can invalidate the process.
Building Owner
The party proposing the notifiable works and serving the notice(s).
Tip: If you’re the one altering, excavating or building on/near the boundary—you’re the Building Owner.
Adjoining Owner
Any owner of land/buildings/rooms adjoining the Building Owner’s land. For excavations (s.6), an owner can be “adjoining” even if not physically touching—distance triggers the status.
The walls and structures
Party Wall (Type A)
A wall standing astride the boundary and forming part of a building on at least one side.
Think: The shared wall in semis/terraces where the boundary runs through the wall.
Party Wall (Type B)
A wall standing wholly on one owner’s land but used by both owners to separate their buildings (e.g., you build against your neighbour’s wall—where you abut, that part becomes “party”).
Key point: Only the separating portion is “party”.
Party Fence Wall
A free-standing masonry wall (not part of a building) that stands astride the boundary and separates lands—e.g., a brick garden wall.
Not included: timber fences or hedges.
Party Structure
Not quite a wall! This includes floors, partitions and other structures separating parts of a building approached by separate stairs/entrances—classic in flats/maisonettes.
Why it matters: Works to ceilings/floors between flats are notifiable under Section 2.
External Wall
A wall forming part of a building that stands wholly on one owner’s land and may be up to (but not astride) the boundary.
Practical effect: Often relevant when building a new wall up to the line of junction under Section 1(5).
Boundary Wall
A free-standing wall (not part of a building) standing wholly on one owner’s land at, but not astride, the boundary (ignoring projecting footings).
Don’t confuse: A boundary wall is not a party fence wall unless it stands astride the boundary.
Foundations & ground
Foundations
Includes footings beneath a wall. The distinction matters for excavation notices (s.6) where depth relative to a neighbour’s foundation base decides whether the work is notifiable.
Special Foundations
Foundations where an assemblage of beams or rods (i.e., reinforcement) is used to distribute load—effectively reinforced foundations.
Crucial rule: You cannot place special foundations on your neighbour’s land without their written consent, even if other foundations could lawfully project.
Locations & distances
Line of Junction
The legal term for the boundary line between neighbouring lands.
Relevance: Section 1 notices deal with building on, up to, or astride this line.
Adjacent Excavation
Excavations within 3 metres (to a deeper level than your neighbour’s foundation) or within 6 metres where the work intersects the 45° plane drawn from the bottom of the neighbour’s foundation (Section 6).
Common trap: Owners often think the Act is “only about walls”—Section 6 is about ground and triggers notice even when no wall is touched.
Doing the work
Work “in pursuance of the Act”
Notifiable works executed under the rights in Sections 1, 2 or 6.
Why it matters: Only these works benefit from Section 8 access rights (temporary rights to step onto neighbouring land when necessary and properly awarded).
Raise, Demolish & Rebuild, Cut In, Cut Away
Section 2 lists specific permitted operations (e.g., inserting beams for a loft conversion, removing a chimney breast, cutting flashings). If your proposal matches a Section 2 right, it’s usually notifiable and can be regulated by an Award.
Service & formalities
Notice / Served
Formal notices have to be served correctly (Section 15 sets out valid methods). Wrong addressee or method can invalidate the process.
Practical note: Where there are multiple owners of the same adjoining property (freeholder + long leaseholder), serve each.
Putting it together with examples
- Loft conversion in a terrace: Cutting steel into the party wall = Section 2 works → Party Structure Notice (2 months) to all adjoining owners.
- Rear extension up to boundary: New wall up to line of junction = Section 1(5) notice (1 month). If you want the wall astride the boundary, you need the neighbour’s written consent (Section 1(2)).
- Deep foundations near neighbour: Piles or deep strips within 3m or intersecting the 6m/45° plane = Section 6 notice (1 month) with plans & sections.
- Garden wall astride boundary: That’s a party fence wall; works to it usually fall under Section 2.
Understanding these Section 20 definitions helps you identify what notice to serve, whom to serve, and what rights apply next.
Keep it simple—and correct—with Simple Survey
We’ll translate your drawings into the right notices, served on the right owners, and—if needed—agree a robust Party Wall Award that protects both sides and keeps your build moving.
Transparent, low fees:
- Party Wall Notice service: £25 per adjoining ownership (multi-notice bundles discounted)
- Act administration as Agreed Surveyor (single surveyor): typically £300 fixed-fee (depends on complexity and number of notices/owners)
- Two-surveyor route (we act for the Building Owner): fixed-fee proposals from £325 for our side (we work to keep your neighbour’s surveyor’s hourly fees reasonable and contained)
FAQs
- What is Section 20 of the Party Wall Act?
Section 20 defines key terms like “owner”, “party wall”, and “special foundations”, which decide if works are notifiable and what notices must be served. - Why is understanding Section 20 important?
Getting the definitions right ensures you serve valid notices and avoid disputes or invalid awards. - Who can be considered a ‘Building Owner’ under the Party Wall Act?
Anyone proposing notifiable works — including freeholders, leaseholders, or developers — counts as the Building Owner. - Can special foundations be built on my neighbour’s land?
Only with the adjoining owner’s written consent; otherwise, it’s not permitted under the Act. - How can a Party Wall Surveyor help with Section 20 compliance?
A qualified party wall surveyor ensures all notices and awards are legally valid, protecting both owners’ rights.
Start now:
Email your address and plans to team@simplesurvey.co.uk. We’ll confirm what’s notifiable, who counts as an owner under Section 20, and set up the notices/Award you need—fast, valid, and cost-effective.
Simple Survey — the most cost-effective Party Wall surveyors in England & Wales.