After decades of tweaking you would think that the GPDO might have achieved near-perfection, such that only good quality design would escape the need for planning permission. Not so, sadly, as a recent appeal case in east London indicates (DCS Number 400-017-938).
The inspector found that “the dormer would appear as a dominant and disproportionate addition, which would sit awkwardly against the modest scale of the host roof” and “As such the scale, position and bulk of the dormer would unbalance the appearance of the host dwelling and would be conspicuously at odds with the largely simple and generally unaltered roof-scape…. “
The inspector concluded that the scale and position of the proposed rear dormer would be harmful to the character and appearance of the host building and the locality and consequently contrary to development plan policy. He recorded that Section 38(6) of the Planning and Compulsory Purchase Act 2004 states that applications for planning permission must be determined in accordance with the development plan unless material considerations indicate otherwise. Accordingly, he decided that “The ability and likelihood that within the permitted development rights in the GPDO a very similarly positioned and scaled rear dormer could be constructed with comparable effect on the character and appearance of the locality, is a material consideration. In this instance it signals a determination other than in accordance with the adopted development plan and consequently, the appeal succeeds.”
Permitted development as a fallback position in house extension proposals is covered at section 12.233 of DCP Online.