Neighbour's garden structure

tetrarch

From the sounds of it this is not a "building", but a pergola. As I recall the restrictions for Pergola's close to boundaries are that they cannot be more than 2.5m above local ground level.

From what your describing then your Mum doesn't have any viable legal avenues to pursue

I think that you've correctly identified your role is to de-escalate the situation. IMO the loss of view/light from the structure should be relatively minimal.

IF there is any room for negotiation with the neighbour then a request for the cross rails to be 4x2 rather than 6x2 would reduce the overbearingness (if that's even a word) consideringly

I built a pergola in my previous back garden and the 6x2's I used were a lot more shade-giving than 4x2's. In my case this was deliberate as we had a South facing garden at the time

Regards

Tet

TELLIT01

If the structure is going to be open sided I doubt it will be classed as a building so unlikely the council planning department will be interested.

As others have said, there generally isn't a 'right to light' in a garden.

Yorkie1

Thanks all.

Mum has luckily decided to be more pragmatic about it now. No legal avenues to be pursued

She might go and have a friendly chat with the neighbour to explore the maximum height it will be, and I'll mention the wood size to her as well (though that might go over her head - getting her to understand the concept of a roof which slopes rather than is flat, was an obstacle  )