Minimum gap between properties to avoid weather flashing

[motorbiking]

Neighbour has planning permission to build a single story extension up to his boundary. He is proposing cutting a lead flashing in to my house. This would make the two properties link detached. I know he can't do it without my permission as the new structure would be under my eves and gutters and well over the boundary. Allowing for foundations on his own land, I think there will be a natural gap of around 300-350mm. Currently there is a garage on the boundary (actually over it in places) and we've not had any problems in 50 years.

Are there other solutions? Would a 300mm gap be good enough for ventilation etc.

 

[^woody^]

You don't need any ventilation or any flashing, and the gap can be any dimension. External walls are weatherproof.

 

[motorbiking]

thanks, my gut feel is this is an excuse to make his internal rooms as big as possible.

 

[^woody^]

That may well be so as your wall is on your side of the boundary.

The neighbour just needs to design his roof edge as normal - edge kerb and fall to front if a flat roof, as presumably he wont want a gutter on the boundary