50m3 Calcs under permitted development

1 Sep 2020
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United Kingdom

I would appreciate some advice.

we are currently in the middle of a 2 story extension which includes extending the original loft space. This has been through planning permission and was granted.

we have now decided that whilst the gable wall is down we are going to convert the entire loft space including adding a dormer.

I understand part a of the 50sm3 regulation regarding the dormer but part b say something about including all space including existing extended space.

when working out the square meters should I be adding the new loft space that was part of the original project granted by planning permission or is it just the extra space from the dormer? Secondly if it is the entire new part of the loft and dorma then is it just habitable space or the entire space?

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The 50cu.m will normally take into account the extended roof space, habitable/usable or not. The majority would struggle to meet the volume uplift for a roof extension of an original roof along with a dormer. Why not consider formal Planning as opposed to PD?
Thanks for the reply. We don’t have time for planning. It is all a bit of a last minute decision.

Is the space measured externally ? It’s only a 2 up 2 down so we might just get away with it.
Planning takes the external footprint while BR’s takes the internal footprint.

Just a note... you can’t use PD on something that is not yet built, especially on a part of the building that is not original. If you are looking to convert the new roof space and have a dormer across the original and new roofs, then that would require a revised formal application anyway. The only way you could do that is to build/complete the two storey side extension and then utilise PD after.
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