Answer
Do conservation area rules apply to my back garden?
Yes, they apply to the whole property, though they often bite more lightly at the back.
In short
Yes. Conservation-area rules apply to the whole property, including the back garden, not just the street frontage. They tend to bite on outbuildings, cladding, demolition and trees. The effect is often subtler at the back, but it still needs checking before you start.
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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