Boundary wall collapses are classic areas for neighbour disputes, made worse because a wall, even a small one, can cost a significant amount to rebuild and repair.
Disputes are common because walls typically stand in place for several decades before anybody pays them any serious attention. It can often be the case that the original neighbours on either side of the wall have long since moved on, and nobody actually knows who is responsible for the wall.
If you are facing this situation, your first port of call ought to be to look at your title deeds and plans to see if there is any indication on the documents or plans as to who owns the wall and who, therefore, might have responsibility.
It is often the case that the title deeds and plans are silent as to who has the responsibility. The next thing to consider is whether or not the boundary wall definitively lies on one side of the boundary or the other, or whether, in fact, it is a party boundary wall, i.e., it sits on the legal boundary and is actually shared by both parties.
To determine that issue, again, if the title deeds do not give an answer, it might be necessary to involve a boundary surveyor to give some early advice on whether or not it is firmly on one side or the other of a legal boundary or a party wall.
If it turns out to be a party wall, this means that you might be able to insist that the neighbour shares the cost, but it also might come as a nasty surprise to the neighbour, who might have proceeded for many years on the basis that the wall was nothing to do with them and they have no responsibility for it. It is rare to find a homeowner who has cautiously budgeted and saved for 20 years to pay for repairs to a boundary wall, even if they knew it was their responsibility.
If you receive expert advice that it is a party boundary wall, then the first sensible step would be to have a discussion with your neighbour and see if you can get an agreement on jointly sharing the costs of any repair works that are needed. If that proves to be difficult, your next natural step would be to get legal advice from a specialist party wall solicitor about whether you can take advantage of any of the procedures set out in the Party Wall, etc. Act 1996 to force your neighbour to contribute towards the upkeep and repair of the wall and accept responsibility for part of it.
In a different situation, it might be the case that your boundary surveyor gives you firm advice that the boundary wall was wholly situated on your neighbour’s property and is, therefore, their responsibility. Again, this might come as a shock to the neighbour and be unwelcome news and they may initially be hostile. However, if it is firmly established that the boundary wall is situated on the neighbour’s property and has fallen onto your property, then this would constitute a legal nuisance and trespass and would give you the right to take legal action to force the wall to be removed from your property and depending on the circumstances, potentially rebuilt and reinstated.
It might also be the case that your land enjoyed a natural right of support from the boundary wall, in which case the neighbour’s might have a duty to maintain that natural right of support or take steps to maintain it.
In all instances, the neighbours should try and explore a solution and reach agreement in the first instance, but if that fails then specialist boundary legal advice should be taken.