2 Edwardian semis with 2 different roof pitches on single storey extension

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We are building a single storey rear extension wall next to our neighbour’s single storey rear extension wall.


The neighbour has a pre-finished aluminium capping to their parapet.


We intend to form a pitched roof abutting right up to theirs forming a weathering detail - but this is proving decidedly difficult!


Our roof pitch will not match theirs. Their roof pitch I estimate is 12 degrees and ours, 15 degrees.


Therefore, the lowest part of our roof at wall plate level does not enable a 150mm cover flashing to be formed between the neighbours extension wall and our roof (we can only get say 60-70mm upstand).


At the highest level at rear original house external wall abutment, there is healthy  say 300-400mm difference in levels down to their parapet which would enable a detail to be created (subject to their agreement) dressing on to their parapet.


But the ‘cross over’ space between the two creates a troublesome area difficult to weather properly.


It is not really an option to take off the neighbour’s aluminium capping.


I understand an option is to form my own parapet which would resolve the issue, but I may lose internal floor space.


Any ideas?

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If i understand you 

you are making a lean too extension which you intend to attach to the neighbours wall which is tight up to your boundary .

have you asked them if they will let you  and give permission for maintainence ?

I any water leaks from your roof will go right through their wall  and vice versa 

 It would a hard no from me and i would telling you to build your own wall and keep your rain water to your self  

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