Suppose you have a 2 storey semi-detached house with a single storey
semi attached extension at the rear (typically kitchen / bathroom), how
easy is it to build a 2nd storey above the extension on one half of the
What problems would you have to overcome?
Do you mean that both houses currently have a single storey rear
extension, separated by a party wall, and that you want to build a
second storey on just one of them?
Are you asking from a physical construction point of view, or about
planning issues, or both?
From a planning point of view, your second storey is going to be very
visible from the upstairs of the other semi, and may block a lot of
light - depending on orientation. So you need to discuss this with your
neighbours, and take advice from the planners before going very far.
As far as physical construction is concerned, the wall above the
existing party wall will be an outside wall, and will need to meet
thermal efficiency standards - and will probably need to be quite a lot
thicker than the party wall (cavity vs solid, etc.). So you'll probably
need some steelwork on your side of the party wall to support the extra
thickness. This pre-supposes, of course, that the foundations can
support another storey - as mentioned by others.
Life would probably be easier if you could persuade your neighbour to
mirror whatever you want to build. Some - but not all - of these issues
would then disappear.
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