Answer
Do I need planning permission for a greenhouse?
Normally no, as an outbuilding within the usual limits.
In short
A domestic greenhouse is treated as an outbuilding and is normally permitted development within the usual limits on height, position and garden coverage. The main thing to watch is the 2.5 metre height limit if it sits within 2 metres of a boundary, and the tighter rules on designated land.
A note
General guidance, not advice. Rules vary by site, and Article 4 directions or conditions can change what applies. Check with your local authority and the Planning Portal.
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