There is no legal convention, it is a legal myth, where the property on the left is responsible for one boundary and the property on the right the other. The same applies when one property is higher than the other.
If one property was built later than the other, would be the responsibility of the later addition normally.
If the properties were built at the same time, then it’s a joint responsibility.
If one party will not agree to pay half of the cost of any remedial work, then the other party will have to do the work, pay for it and then seek the cost from the nonpaying party, through the Small Claims Court if necessary.
Can I clarify anything else for you?
Please rate the service positive. It doesn’t cost you anything but helps me greatly.
We can still exchange emails. Best wishes. FES.
PS assuming there is no mention in the deeds of who is responsible for which boundary.
If there is going to be an argument over it, for the cost of the argument compare to the cost of the flashing, the insurance company would settle 50-50.the other thing of course is that if the neighbours is it yours and you say it’s the neighbours, cost of taking this to court is also probably going to be more than cost of the repair although if your claim is successful, you would normally recover those costs from the unsuccessful defendant. If the houses were built at the same time, I’m inclined to think that it’s a joint responsibility.
If you can attach some photographs, I may be able to give you a firmer opinion.
I see that you have given a negative rating. Was that a mistake? You appreciate, that I’m not responsible for the way that the law would interpret this. Please remember also that I haven’t seen any photographs and it’s very difficult to visualise the physical layout of the property.
Is there anything I didn’t explain clearly enough?
Thank you that’s very kind.