Does 45 degree rule apply for permitted development?

Walshy252

We moved in to our 3 bed semi in the summer last year and after overcoming some issues with neighbours and their building negligence which caused some damages to our property, we seem to be on good terms mostly due to my good nature on the situation in the hope that it would make a future extension less troublesome. The neighbour is actually a representative of an investment company which owns the property and is current renovating the interior to create a dental workshop for a local dentist down the road. The property therefore will move from being a habitable space to a commercial use, though I'm unsure if the change will have been recorded with local authority.

I have included a diagram which details the proposed extension in green as well as the layouts of both properties. From day one we wanted to extend to the rear to create the open plan living and dining set up that is becoming more and more popular. The design principle is a fairly straight forward one and as you can see from the diagram will involve extending the dining room out by c. 2.5m to level the existing kitchen, and then what would have been the external kitchen wall and support the bathroom above with a steel. The new development would then be covered with a shallow pitched roof with skylights/velux to maximise the light and internal space. On both properties, I believe the kitchens and garages are part of the original design.

Unfortunately the design is where the simplicity seems to end as we now venture in to the complexities of planning and regs that could bring the dream space crashing back down to earth. As I understand it, our proposal would not satisfy the conditions for planning permission in that it woud breach the 45 degree rule for the neighbours rear window. However I believe that the proposal satisfies all criteria for permitted development, and therefore would not require planning permission. So does that mean that the 45 degree rule would be null in this instance also?

Having read the technical guidance on permitted development, there is no reference to 45 degree rule beyond the building position relative to the highway. In all my research so far I have found all reference to 45 degree rule under planning guidelines rather than building regulations. On the face it would appear that I could proceed with my plan under permitted development with no interest from the council whatsoever beyond the normal building regs.

I have no issue whatsovever with the light obstruction, partly because of the significant damages and costs I have incurred as a result of their negligence, but mostly because of the fact that the property is intended for commercial use so comfort of daylight is less important. That said, it seems quite a big loophole that could cause some controversy if the situation was different so really I'm looking for some thoughts on how to proceed. Can we proceed under permitted development or does the 45 degree rule still apply and if so, under what grounds?

Other facts:
- Neighbour has used their permitted development by building a 30 sqm garage in the garden
- Our conservatory is a UPVC and appears to be at least 25 years old given the look and feel
- Both gardens are South facing