Permitted development allowance loft?

7 Feb 2020
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United Kingdom
Could anyone please advise on the volume limits under permitted development?
My house already has an extension, and I would like to convert the loft with dormer(s). Is the total allowance under PD 50 cubic metres? And if so is that for all development? Or just extensions? Are loft conversions calculated in this or separately? Thanks
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Just to note the 50cu.m allowance applies to semi-detached houses and 40cu.m applies to terraced houses.

The PD rules for extensions are different to loft conversions.
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Yes the allowance is purely for the converted existing roof, and is distinct from any extension volume.

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