ask us a question on permitted development           Permitted Development England
How to build a home extension  without Planning Permission using your PD rights - Oct. 1st 2008



Home Page About Us FAQ Advertise on this site Disclaimer Privacy Contact Us Site Map

Appeal Decision 70 - Certificate of Lawful Development.

This appeal decision summary and assessment has been produced by Planning Jungle Limited.  For more information, please go to

January 2010 - Code a00070


Summary of Case (appeal dismissed): 


The property is a two-storey semi-detached house. The main part of the roof is a typical dual pitch from front-to-back with a gable side; however the rear-facing roof then merges into a side-facing roof of the equivalent of a full-width two-storey rear projection. The application was for a proposed mansard that would not only have covered the entire rear-facing roof, but also would have projected rearward onto part of the side-facing roof. As such, the rear elevation of the proposed mansard would have been further rearward than the main rear eaves (which would then cease to exist), rather than set-back 20cm from the latter. As this situation is difficult to describe, please refer to the submitted plans. 


The key issue was whether the proposed mansard would be contrary to Class B, part B.2(b), which states that “Development is permitted by Class B subject to the following conditions … (b) other than in the case of a hip-to-gable enlargement, the edge of the enlargement closest to the eaves of the original roof shall, so far as practicable, be not less than 20 centimetres from the eaves of the original roof”. 


The appellant accepted that “if a simple box dormer was being proposed, then it is quite easy to ensure that the vertical face of the dormer sits 20cm up from the eaves”. However, the appellant stated that in this case the “proposal seeks to create a mansard-type dormer that maximises the opportunity to achieve extra space by taking advantage of the lower roof over the first floor bathroom”, which makes it “impossible to retain the short section of eaves of the original roof, let alone set the dormer 20cm up from this point”. The appellant argued that the phrase “so far as practicable” in the condition permits development in such circumstances. 


The Inspector noted the explanatory memorandum to the 2008 legislation, which was laid before parliament and which stated that purpose of this condition was to avoid an entire rear roof being replaced. The Inspector then stated the following: 


“The appellant accepts, and there is no reason to disagree with him, that this situation could be avoided by designing an enlargement where the edge closest to the eaves would be not less than 20cm from them. It is therefore practicable to comply with the condition and the appellant’s proposal fails to do so because he has chosen to submit a noncompliant design. The design may maximise the opportunity to achieve extra space and it may look more attractive than compliant designs, but these are considerations related to its planning merits, which are outside the scope of the appeal since there is no planning application to be decided.” 


Main Conclusions: 


·       The desire to have greater floor space in a proposed roof extension is not a sound basis to show that a 20cm set-back is not “practicable”.
[Relevant to: B.2(b)].


Links to the “Appeal Decision Notice” and other associated documents (e.g. drawings, etc): 


·       Appeal Decision Notice: 

·       Elevations: 





Download documents and diagrams of useful

Permitted Development information

permitted development documents download

 Appeal Decisions