Is it still PD (outbuilding with neighbour using the boundary line)

18 Oct 2013
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United Kingdom
Our neighbour and I have decided we would like to replace his fence line with a new wall or fence and make a contribution since it was my request to have it renewed. As part of this work, he is considering erecting a brick outbuilding of a somewhat irregular shape to accommodate the odd shape of where his garden ends (diagonal end wall).

He wants to use his fence/border line to construct one side of the outbuilding wall. They have asked us if we want to share this wall to create an outbuilding on our side too. The result of this will be something that resembles a semi detached outbuilding where both parties are using the boundary line which then extends some 30m of new fence or brick wall line.

Would this development be considered PD if both neighbours each keep to within the 15m2 area space (and 2.5m height) since we are building within the 1m boundary rule (or in actual fact on the boundary line with no gap at all)? We can sign a Party Wall agreement if need be but both sides are happy to proceed anyway without it.

My gut feeling is that this is PD, but I'm not too sure I would be happy with the aesthetic look of the development at the end of the garden. I am tempted to build something a little bigger than 15m2 and keep it 2m away from the boundary line.

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The 15m2 rule is a building regs thing. You can build as big a footprint as you like as long as it is less than 50% of the garden from a planning/pd point if view. Basically under 15m2 you can build how you like, under 30m2 it must be built of non combustible material or 2m away from a boundary, over 30m2 you'll need building regs.
But if you have one of those big 7x4m expensive log cabins, are they not considered combustible or wood?

I guess also my question was more concerned with two neighbours' outbuildings being attached across the boundary.
I recall a thread about this a while back (I think), have a feeling that the consensus was that it would not be PD but I'm blowed if i can find it.
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Thanks Freddy. Yes I spoke to my architect just now and he said something similar. It is only PD if it is built within the curtilage. Shame.
This is a reply I got from the council.

That is an interesting question, which I've not been asked before.

In order to be Permitted Development an outbuilding would have to be within the curtilage of the property. You could build an outbuilding with its flank wall touching (but not crossing) the side boundary, and your neighbour could do the same thing. In that case the two outbuilding would abut each other. I cannot see that there would be much difference between that and the approach that you are suggesting, of building the two of them together as one development - so long as there is an internal division wall which is exactly on the boundary.

This is my own opinion. The only way to get a formal decision from the council on the matter is to apply for a Lawful Development Certificate.

If one brick or one tile in a stretcher bond format crossed the so called boundary, if we really wanted to be anal about it, it could be considered a breach.

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