Neighbour building to boundary wall - Considerations...
Discussion
We finished our extension back in 2023, and now our neighbours want to do something similar. They don't communicate and have a poor understanding of neighbourly consideration, so I wish to understand matters clearly before engaging with them. I'll take the necessary legal advice as required.
Anyway, I am not petty-minded and don't really have any objection; I simply want to make sure they play nice as relations are strained for reasons I won't bore you with...

My understanding is: in the image above, the wall I've highlighted in green sits entirely inside our boundary, whereas the tiled section would be considered a party wall as it straddles the boundary line in red.
Their proposed plans appear to suggest a similar arrangement to ours, although the drawings on the planning portal are light on detail. They show no gutter arrangement at all and contrast with the detailed architects' drawings we had commissioned for our build.
In essence, they will need to tie into our boundary wall and would need a hidden valley gutter like ours, whether it is on their plans or not.
I want to understand the legality of tying into our newly constructed boundary wall. Do they need our direct consent, or is this no different from a party wall?
p.s. Ignore the abysmal finish on the single-ply work; it's all earmarked for removal and replacement in lead.
Anyway, I am not petty-minded and don't really have any objection; I simply want to make sure they play nice as relations are strained for reasons I won't bore you with...
My understanding is: in the image above, the wall I've highlighted in green sits entirely inside our boundary, whereas the tiled section would be considered a party wall as it straddles the boundary line in red.
Their proposed plans appear to suggest a similar arrangement to ours, although the drawings on the planning portal are light on detail. They show no gutter arrangement at all and contrast with the detailed architects' drawings we had commissioned for our build.
In essence, they will need to tie into our boundary wall and would need a hidden valley gutter like ours, whether it is on their plans or not.
I want to understand the legality of tying into our newly constructed boundary wall. Do they need our direct consent, or is this no different from a party wall?
p.s. Ignore the abysmal finish on the single-ply work; it's all earmarked for removal and replacement in lead.
Edited by DoubleSix on Monday 25th August 20:12
lizardbrain said:
I'm curious what your communication was like when you built the extension.
A model of how it’s done.Invite them round prior to submission, review, discuss, invite comment.
Bottles of wine when things go wonky, heads up prior to noise etc.
Honestly, we went way beyond any reasonable requirements and our other neighbours have all been awesome.
I did actually have a chat with party wall expert today and he confirmed my thinking that anything attached to my boundary wall would need express consent and fall beyond the party wall act.
Still interested in what the PH hive mind has to say however…
Edited by DoubleSix on Tuesday 26th August 22:44
Edited by DoubleSix on Tuesday 26th August 22:45
My experience is from when the PWA was pretty new.
It was easy to find 'experts' who disagreed about what it meant.
How far inside your boundary is the outer face of your wall?
How accurately can you prove where the boundary is?
I suspect that unless the outer face of your wall is inside your boundary by a definite distance, then you won't stop the neighbour tying into the face of the wall.
What outcome are you hoping for?
How different from that is what your neighbour wants?
It was easy to find 'experts' who disagreed about what it meant.
How far inside your boundary is the outer face of your wall?
How accurately can you prove where the boundary is?
I suspect that unless the outer face of your wall is inside your boundary by a definite distance, then you won't stop the neighbour tying into the face of the wall.
What outcome are you hoping for?
How different from that is what your neighbour wants?
Who took that photo? You? Were you leaning into their garden to do so? Did you have permission to do so and take it?
I know its off topic, but if I found that my neighbour has posted a photo of not only my house/garden, but a view into a window of my house onto the internet, I'd be very unhappy.
I know its off topic, but if I found that my neighbour has posted a photo of not only my house/garden, but a view into a window of my house onto the internet, I'd be very unhappy.
DoubleSix said:
Just a solid understanding of the situation as a party wall which becomes a boundary wall is somewhat nuanced.
In the absence of any actual expertise here i’ll seek professional advice of course.
So you don't have objection to him doing the same as you in practice, it's just you want the legals sorted?In the absence of any actual expertise here i’ll seek professional advice of course.
or are you planning to object to the development?
OK. I'm probably totally wrong here but .........
Assuming the neighbour is on the left of the photo and you were hanging over your fence to take that photo, or using a selfie stick.
Looks like they had a single story extension before you had your larger extension.
But they managed to place a row of tiles well over the boundary onto your property?
How does that happen?
Like a previous poster said - how do you know where the boundary is?
GPS mapping can get you down to cm resolution, but you need to be able to relate that accuracy to features on the ground.
Assuming the neighbour is on the left of the photo and you were hanging over your fence to take that photo, or using a selfie stick.
Looks like they had a single story extension before you had your larger extension.
But they managed to place a row of tiles well over the boundary onto your property?
How does that happen?
Like a previous poster said - how do you know where the boundary is?
GPS mapping can get you down to cm resolution, but you need to be able to relate that accuracy to features on the ground.
lizardbrain said:
DoubleSix said:
Just a solid understanding of the situation as a party wall which becomes a boundary wall is somewhat nuanced.
In the absence of any actual expertise here i’ll seek professional advice of course.
So you don't have objection to him doing the same as you in practice, it's just you want the legals sorted?In the absence of any actual expertise here i’ll seek professional advice of course.
or are you planning to object to the development?
Given their attitude during our build i am not going to be passive, but also not inclined to be obstructive.
OIC said:
OK. I'm probably totally wrong here but .........
Assuming the neighbour is on the left of the photo and you were hanging over your fence to take that photo, or using a selfie stick.
Looks like they had a single story extension before you had your larger extension.
But they managed to place a row of tiles well over the boundary onto your property?
How does that happen?
Like a previous poster said - how do you know where the boundary is?
GPS mapping can get you down to cm resolution, but you need to be able to relate that accuracy to features on the ground.
The tiled section is a party wall. The boundary is where i have shown it.Assuming the neighbour is on the left of the photo and you were hanging over your fence to take that photo, or using a selfie stick.
Looks like they had a single story extension before you had your larger extension.
But they managed to place a row of tiles well over the boundary onto your property?
How does that happen?
Like a previous poster said - how do you know where the boundary is?
GPS mapping can get you down to cm resolution, but you need to be able to relate that accuracy to features on the ground.
Honestly, no offence intended, but if you’re struggling here, you are not the poster im looking for

Lotobear said:
Your neighbour has the right, under the PWA, to enclose upon 'your' wall without building their own. The wall then becomes a party wall.
Possibly a bit off topic but...What if you decide to knock your wall down?
My MIL lived in a detached 1920s house with a back door at the side of the property. She built "lean to" with a wall on the boundary. Her neighbour then built an extension and we assume he used her wall as his wall.
If the new owner of the MIL's house decides to reinstate the original appearance then the neighbour is going to have a very draughty kitchen.
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