There is a tangled legal matter here and a neighbour conundrum.
When we moved in to our house we had hedges on either side - the dreaded Leylandii - two cuts a year minimum!
We stuck it for six years and then approached out neighbours on both sides about removal and replacement with a fence,
We didn't want a heavy wall.
Our neighbours went half on the new fence and we paid for removal of the hedge.
Fence is a 6ft [1.8M] concrete post and treated timber panel job from Abwood - €1800 to you squire.
I should say that the end of the garden had been done by our neighbours to the rear a couple of years ago - same principle - they paid fhri their trees to go and we went half on the fence.
Loss of a hedge can be a bit of a twinge, but I'd be a little wary of the wall.
Consider the alternatives and cost, particularly the cost of matching on both sides and the rear.
If your other neighbours don't want walls you could be left with a very lop-sided garden.
I think going half for the fence confirms joint ownership.
If you cannot agree, there is the legal thing - all the below is mere speculation on my part and you should take legal advice.
I think the whole loss of privacy thing may be backed up in some areas by development plans seeking retention of mature hedgerows, but I think that relates to stuff in the public domain.
I think you can stop them taking out the whole hedge if things get nasty by issuing a solicitors letter, telling them to restrain themselves to over hanging branches on their side.
Cutting half the boughs/roots could kill the hedge and this is where the legal eagle comes in.
They certainly cannot build the centre of the wall on the boundary if you do not agree to it - I think you can demand that their foundation must be kept wholly on their side and you could be really obstructive if you wanted to be.
I offer the following comment as is, without qualification or endorsement
From:
[broken link removed]
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Leylandii and the law
In Britain and Ireland, x Cupressocyparis Leylandii is estimated to be the cause of over 20,000 ongoing neighbour disputes. The disputes usually centre on encroachment or the exclusion of sunlight; many of these problems end up in court or worse still, the local accident and emergency room.
Here is the leylandii tree law as it stands in Britain…
• If Leylandii or another form of hedge is encroaching on a neighbour's garden, the neighbours is entitled to trim back the hedge to the boundary themselves, but must return the trimmings to the owner. This law also pertains to Ireland as well. That solves the sideways growth of the tree for a while, next is the upward growth. You are not entitled without permission to reduce your neighbours tree in height, often done to allow extra sunlight to sites. This is where your people skills will be put to the test as you try to convince your neighbour to top his trees or allow you permission to do so.
• In Britain, if the neighbour digs his heels in and stubbornly refuses to reduce the height of the trees or hedge, then you can contact you local council. A complainant must prove they have tried to resolve matters privately first before approaching their local council. If the council deems the hedge excessive, they can ( under the anti-social behavior act 2003 ) order it to be reduced in height to two metres.
• Failure to comply with this order could mean a fine of £1,000.
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I seem to recall that Dick Roche toyed with the idea of a 2M restriction in legislation but I don't think it ever came to much.
There is obviously a legal confusion here.
Developments have been stopped due to their diminishing the amenity of adjoining sites and I think there is even a BRE Report on it in Britain in relation to how much sunlight a house site should get.
It seems ridiculous that you can grow monster Leylandii hedges [I know of one over 12 ft - 3.6M tall] or worse, two storey Pine Tree boundaries.
Anyway, 'nuff said,