Can a Neighbor Build Over a Boundary Line?

It’s always nice when we are open and friendly with our neighbors, but not all neighbors fall into this category. In fact, some can make life rather difficult!

Nobody chooses their neighbors, but if you have a clear and open line of communication you can always discuss questions like ‘can a neighbor build over a boundary line’ and discuss the legalities as well as the practical elements.

However, if you don’t have this type of relationship with your neighbor or you’re wondering whether they are allowed to build over your boundary line, you will probably have a few questions.

Your neighbor is typically only allowed to build up to the property’s boundary line, or the line of junction, between the properties.

However, there are some circumstances when they are allowed to build over a boundary line on your actual land.

When Can a Neighbor Build Across the Boundary Line?

Let’s take a look at some examples of where a neighbor might be allowed to build on your land:

Ground Floor Extension

If a neighbor wants to construct a new party wall as well as foundations on your property, they need to ask you for consent.

The existing boundary wall constructed on both parties’ land can be taken down before being rebuilt as a new party wall.

If the wall needs to be thickened (eg changed to a cavity wall from a single wall) then this would have to take place on your neighbor’s land, not yours.

Your neighbor’s foundation for the extension can be constructed on your land if it needs to be. In practice though, foundations rarely have to be built over the boundary.

Whether the extension is for a one- or two-story foundation, it doesn’t usually need to extend past the boundary.

Your neighbor doesn’t have the right to build a reinforced concrete foundation on your property without your consent.


Attic (Loft) Extension

Your neighbor might want to build an attic extension which will entail increasing the party wall height.

This wall is shared in ownership between you and the neighbor. It isn’t the case that each of you owns one half of it.

Whoever is carrying out the building work is allowed to raise the party wall for full or part-width.


Underpinning and Basements

It is the right of your neighbor to underpin the party wall if he wishes to do so. If this is the case, he can put the underpinning on your land.

This might not be so straightforward, in that there could be reinforcements. This is likely if reinforced concrete is being used.

If your neighbor wants to build a basement or excavate near the side of your property, he is legally allowed to underpin or to safeguard your building’s foundations in another way.

After that, he can add new underpinning (or foundations) on your properly. Again, this can happen but it is very rare.


Can I Build Over the Boundary Line?

If it’s you that wants to construct a fence or wall over the boundary line, you need to serve a notice to your neighbor ahead of the works. You need to tell him in writing what you are proposing to do.

Many people prefer to hire a party wall surveyor to do this on your behalf. If your neighbor objects, you don’t have to right to build over the boundary wall.

In this instance, you might need to alter your plans and ask again. This is why it’s best to consult with the neighbor early on, to save time and money.

If you want to build a wall on your property but against the boundary line, this also requires permission from the owner of the neighboring premises.

A wall constructed entirely on your land will not be a party wall, whereas a wall astride the boundary wall is a party wall.

Building on your own land (even near the boundary) doesn’t require you to notify the neighbors, but if you need to form foundations there, you might need to serve a notice. This depends whether their building is near enough.

How Long Before Building Should I Serve a Notice?

You need to serve the notice at least 4 weeks before the planned starting date.

If the neighbor agrees with the works in writing then it can go ahead.

If he objects or fails to respond then you have to construct the wall on your own property and at your own expense.

Sometimes the cost of building on the boundary line can be shared between you if the wall is going to be shared (eg a garden wall).

The surveyors are typically the ones deciding who pays for what unless it’s clear. The whole cost is almost always met by the one doing the work.

If the neighbor wants to use the wall in future, they might have to pay compensation to whoever built the wall in the first place.

Remember the neighbor doing the work has the right to put ordinary footings for the new wall on or slightly over the boundary line if absolutely necessary.

What Happens if We Can’t Agree?

Party wall surveyors need to be hired if you and the neighbor are unable to agree on any work astride or beyond the boundary line.

In Conclusion

Although this situation is comparatively rare, if you want to know whether a neighbor is allowed to build over your boundary line, it does depend on the specifics.

Hopefully the above guidelines will help you to figure out whether or not your neighbor has the right to extend construction over the shared boundary line.

If you have any other questions though, it is probably a good idea to check your deed restriction documents and/or hire a surveyor to assist you.

If your neighbor is happy to use the same surveyor, then he can work for you both for the one fee.

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