Section 1 of the Party Wall etc. Act 1996 deals with new walls at the boundary line, often called the line of junction. It is a crucial part of the Act for extensions, infill builds and other projects where a new wall is proposed at or on the boundary. Homeowners frequently assume they can simply build astride the line because it looks efficient on a drawing. In law, the position is more controlled than that. This guide explains the practical distinction between a new wall built astride the boundary and one built wholly on your own land up to the boundary, and how Section 1 usually operates in London projects.
What does “line of junction” actually mean?
The line of junction is essentially the boundary line between land in different ownership. Section 1 is engaged where the building owner proposes a new wall at that line rather than works to an existing party wall. That makes it different from the usual Section 2 party structure route and different again from Section 6 excavation procedures.
In practice, Section 1 questions often arise on side return extensions, rear extensions near the boundary, replacement boundary walls and some new-build situations. That is why Section 1 often overlaps in real life with boundary interpretation, excavation planning and neighbour communication. Our boundary wall service and rear extension Party Wall service are commonly relevant when Section 1 needs careful handling.
Section 1 issues that commonly cause confusion
Assuming a new wall can always be built astride the boundary without neighbour consent.
Confusing a new boundary wall with works to an existing party wall.
Overlooking the possibility of projecting foundations under the adjoining owner’s land.
Missing the difference between a wall astride the boundary and a wall wholly on your own land.
Treating Section 1 timing as if it were identical to all other Party Wall routes.
Failing to coordinate Section 1 issues with wider extension or excavation notices.
Astride the boundary or wholly on your own land?
Proposal
Practical meaning
Key point
Wall astride the boundary line
The new wall would sit across land in different ownership
Written consent is important; if the adjoining owner does not agree, the building owner usually cannot insist on this route.
Wall wholly on your own land up to the boundary
The new wall remains entirely within the building owner’s land
This is often the fallback route where astride-boundary consent is not given.
Notice timing and practical planning
Section 1 matters usually require one month’s notice. That sounds simple, but the design implications are often more significant than the timetable alone. If a wall has to be redesigned to sit wholly within the building owner’s land, that can affect floor area, structure, drainage and the coordination of foundations. This is one reason boundary questions should be checked early rather than after the extension layout has been fixed.
If projecting foundations are proposed or the works interface closely with excavation, separate technical and statutory considerations may also arise. For some projects, a Section 6 excavation review is needed alongside the Section 1 analysis.
Why Section 1 disputes are often avoidable
Many Section 1 disputes are not caused by hostility so much as surprise. A neighbour receives a drawing showing a wall on the boundary and feels they are being asked to give away rights or accept a design they do not understand. Good early explanation, clear plans and a realistic fallback position can make these matters much easier to manage.
If the project is likely to be neighbour-sensitive, it is often sensible to involve a specialist surveyor before the notice goes out. Hourican Associates can advise on the correct route and prepare valid notice documentation through our Party Wall notice service.
Frequently Asked Questions
It is essentially the boundary line between land in different ownership.
You should not assume so. A wall astride the boundary raises a different issue from a wall built wholly on your own land up to the boundary.
The project may need to proceed, if at all, with the new wall built wholly on the building owner’s own land instead.
Section 1 matters usually require one month’s notice.
No. Section 1 is about new building on the line of junction, not works to an existing party wall or party structure.
Yes. A boundary build can also involve excavation issues, depending on the foundations and the position of neighbouring structures.
Planning a wall at or on the boundary line?
Hourican Associates advise on boundary wall and Section 1 matters, including valid notice drafting, design implications and neighbour communication for London extensions and infill works.
General information only. The Party Wall etc. Act 1996 applies in England and Wales. This article is not legal advice and does not replace project-specific advice from a suitably qualified surveyor, structural engineer, building control professional, or solicitor where required.
Are you planning a building project – perhaps an extension, loft conversion or basement – that is on or adjacent to your property’s boundary line? Or has a ‘Party Wall’ notice dropped on the doormat informing you of a neighbour’s impending works?
It’s essential to understand all the implications of building plans. If you don’t, it could cost thousands. Our job is to ensure everything is done correctly – and that it doesn’t!
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Richard took the time to walk us through all our options around the boundary wall, explaining exactly what we could and couldn’t do without unnecessary jargon. His guidance was practical, balanced, and gave us real confidence in how to proceed.
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R Sodhi
15 Mar 2026
Richard Hourican was excellent in handling the party wall matters for our new build. Communication was great throughout and everything was handled efficiently, which made the whole process much less stressful. Would highly recommend!
Nigel Ward
08 Mar 2026
Richard and his team acted as party wall surveyor on our renovation/extension project in Richmond. They have been on the ball, polite, very good with neighbours (2 out of the 3 neighbours accepted them as surveyors), and efficient at closing out the Awards. The Awards are comprehensive and clear. Fees are very fair.
James Lemon
07 Feb 2026
Richard was a great recommendation and went above and beyond to arrange complex party wall agreements for both sets of neighbours.
He worked well with our border team as plans changed and then came together and was highly professional and collaborative. Arranged monitoring and liaised and communicated with everyone smoothly.
Would be a great addition to any building project.
Sam Donald
03 Feb 2026
Richard was fantastic to work with - very efficient and knowledgeable, and got the work done with minimal fuss.
Nicole Cruise
13 Jan 2026
Richard was excellent to work with, we have 6 partywalls to complete in a short time and he kept us up to date throughout and chased daily to make sure they were done on time.
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09 Jan 2026
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I'd recommend him
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20 Nov 2025
Absolutely brilliant service. H&A assisted us on an urgent basis with a schedule of condition. They were prompt, efficient and extremely professional. The quality of their work speaks for itself. I would highly recommend them.
Hoe
25 Oct 2025
Richard has been extremely helpful when dealing with my queries about my neighbour extension works even after he was informed that he was not appointed as the party wall surveyor due to some communication issues. A great way to handle such situation professionally.
Emma Charlotte
14 Oct 2025
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21 Aug 2025
Richard was first class with how he helped me with my query. Despite immediately realising Hourican Associates couldn't help me with the work i required, he spent 15 minutes on the phone discussing my problem and directing me to other trusted professionals who could help me. Thanks!!
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15 Aug 2025
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