I would be grateful for some advice. I have an old barn in my garden which is owned by my neighbour. The wall on my side is a designated party wall and is suffering badly from mortar bee infestation which has led to severe degradation to the fabric of the wall and needs to be repaired, this has been confirmed by a structural engineer. My neighbour and I agree that it needs to be repaired but who pays the cost? My neighbour thinks it is entirely down to me, is he correct? Also, this wall is one of the supporting elements to the roof of the barn. What are my liabilities with respect to the roof?