Paul17

I appreciate that. I'll try to find the guidance again, but i don't think it was mentioned in the council's guidance at all, i believe i found the reference online. However, according to the council's website you can't strictly speaking build over 3m high or 3m long anyway without needing planning permission in principle, but in practice they do allow a bit of leeway in each direction.

Hi Temp, thanks for the confirmation that planners are capable of rejecting an application if it fails either of the parts of the 45° rule, that was what I was trying to determine. I also appreciate the anecdotal evidence that happened to you. Hi Devildamo, Thanks for your input. In fact I no longer have the exact source for the requirement that a build 'must fail both plan and elevation views' in order for 45° rule to be applicable (but i did read it somewhere). However i was trying to determine if that was actually the case in practice rather than just in principle, to determine how seriously I should take the possibility of the extension being refused planning permission if it failed in just one direction rather than both.

Thanks for the help. Temp, we have concerns about the 45° rule as the point is that the extension doesn't meet permitted development limits as they stand. Also when you say that: "Yes normally you need both plan and elevation to meet the 45 degree rule" do you mean that we need both plan and elevation to meet the rule so as not to fall foul of it, or does the neighbour needs the extension to exceed 45° in both aspects to use the rule against the build? Devildamo, I don't have a link I'm just trying to determine whether meeting only half of the 45° rule is sufficient for it not to be a concern (if we'd have to fail both plan and elevation for it to become one). The affected windows are serving a habitable room i.e. the kitchen. It seems unlikely that the 45° rule would only apply to two-storey extensions as they'd undoubtedly automatically fail the 45° rule in both aspects. So are there any grounds under which the neighbour can legitimately object to the one-storey build (as it oversteps standard planning development limits but doesn't fail both parts of the 45° rule) and which could cause us to have to adapt the design?

It is slightly larger than the standard permitted decelopment then, as it should be no more than 3m high by 3m long, but is 3.2m high and 3.4 metres long, which is why it exceeds 45° on the plan view by so much. So does the 45° rule have to absolutely be exceeded in both plan and elevation views, before the council planners would look into it the extension more closely? Thanks

Thank you Temp. Yes you're quite right about BRE 209 only applying if the extension were opposite, not side-on. What exactly is classified as permitted development for the 45° rule not to be relevant? In any case, does the 45° rule have to be fully met i.e. both plan and elevation views, before council planners would look into it more closely, especially as one angle is over 60° and the other is close to (though still under) 45°?

I'd appreciate any guidance anyone can give me here, in relation to the likelihood of obtaining planning permission if requested. Firstly, can the 45 degree rule be applied to prevent planning permission if only the plan view exceeds it, but not the elevation view? The specifics are that the extension is 342cm outward length and 320cm high, positioned at 170cm away from the centre of next door's rear kitchen windows. Therefore it's about 64 degrees in plan view for the length, which is clearly excessive, but only about 41 degrees in elevation view (given that the centre of the kitchen windows is about 170cm high), so that's within normal limits. So does the 45 degree rule still apply? Secondly, if the rear kitchen window consists of 3 vertical sections of window, the central section of which consists of a window 2/3 the height of the frame, with a smaller window at the top making up the other 1/3, is the position of the 'centre of the nearest habitable window' (for the measurements of the 45 degree rule) deemed to be either: 1) the centre of the entire window framed section taken as a whole, or 2) the centre of just the middle of the central 2/3 height window which would be lower than the centre of the entire framed area, or 3) the centre of the right hand section of window only i.e. the section closest to the extension. Thirdly, even if 1) or 2) applies, meaning that angle of elevation is under 45°, the proposed extension still fails the BRE 209 test, because when measured at 2 metres high from the midpoint of the central window section, it is a further 1.2m up to the top of the extension and 1.7m away from it, thus giving an upward angle of 35.2°, which comfortably exceeds the 25° limit. Fourthly, should it still be a concern that the plan view angle is so large, given that: A) the 45 degree rule would strictly only apply if both the plan and elevation angles exceed 45 degrees? B) the excessive 64 degree plan angle combined with the 41 degree elevation angle makes a total of 105 degres which is overall quite considerable? C) for at least 6 months of the year an angle of elevation of 41 degrees is still significant since the lower angle of the Sun in the southern sky means that the extension's height of 320cm still casts a full shadow across the neighbour's kitchen windows throughout the day for at least half of each year anyway? Can either the 45 degree rule or the 25 degree rule be used to prevent this gaining planning permission, or is the fact that the sun casts a shadow across the neighbour's entire kitchen window for around half the year the ultimate deciding factor against it anyway? Thanks for any help or guidance you can provide.