Planning departments run on rules of thumb. The 45-degree rule, the 21-metre privacy distance, the various quick tests a busy case officer can apply without leaving their desk: they are useful right up until someone reaches for one on a case it was never designed for.
That is what happened to a family in Weybridge who wanted to extend their home.
The property is a detached, two-storey house at the end of a cul-de-sac off Pennington Drive, one of five individually designed homes. The owners proposed a two-storey side extension, a first-floor addition above the garage, a garage conversion and several new windows: a fairly ordinary enlargement of a family home.
They also held planning permission for a very similar scheme, granted the year before. It had not been built, but remained a lawful fallback if the revised proposal failed.
Elmbridge refused the new application on two grounds, neither of which concerned its appearance. The council accepted that the design was suitable and in keeping with the area.
Its first concern was the effect on Nos 11 and 11a Castle Road, behind the site. The two-storey side extension, it said, would be overbearing and would reduce their light. Its second concern was trees: not enough arboricultural information had been submitted.
Why the 45-degree rule did not fit
The overbearing objection rested on the council’s 45-degree rule, a line drawn from a neighbour’s window to test whether a nearby extension is likely to block its light.
It is a sound enough test, but it is designed principally for houses that sit side by side: the ordinary terraced or semi-detached arrangement in which an extension projects towards the neighbour next door.
The houses on Castle Road do not sit beside this one.
They sit behind it, at right angles, with their rear gardens backing onto its flank wall. A 45-degree line drawn from a window facing the side of the house square-on tells you very little. The council’s own guidance said nothing about how the test should be applied to a relationship like this.
The rule could not settle the question. It came down to what the site actually showed.
What the site actually showed
There was a gap of at least 15 metres between the proposed extension and the Castle Road houses, comfortably more than the height of the new work. It would not cast a significant shadow over their windows or the parts of their gardens closest to their homes.
The extension’s flank would be a blank wall, so there would be no overlooking. It was set away from the boundary, with a roof sloping down and away from the neighbours, and it remained lower than the main house.
The neighbours already looked towards the existing flank wall. The extension would make that wall larger, but being able to see a development is not the same as being harmed by it.
The inspector agreed that the 45-degree test did not fit the geometry of the site. He found the reduced separation unlikely to create an excessively overbearing effect or materially diminish the neighbours’ light.
He also noted that the council’s measurements of the separation distances appeared to be wrong, and that the figures provided by the neighbour were more reliable.
The tree objection
The tree objection was a complaint about missing information rather than evidence of actual harm.
The application form had incorrectly stated that there were no trees within falling distance, and no arboricultural report had been submitted. But Elmbridge had considered an almost identical scheme the year before, when its own tree officer reviewed the survey and raised no objection, subject to conditions.
We supplied an updated assessment for the appeal. It found no harm to the protected trees at the front or rear, and the owners accepted the same protection conditions the council had previously prepared.
The inspector was satisfied that the trees could be protected by condition and allowed the appeal.
Standard tests are useful, but they cannot replace an assessment of the site in front of you. Where a council relies on a test that does not fit the relationship between the buildings—or applies guidance to a situation it was not written for—there may be a good case for challenging the refusal.
Has Elmbridge refused your extension over its effect on a neighbour’s light or outlook?
Send us the decision notice and plans for a free initial assessment. We will tell you honestly whether we think an appeal is worth pursuing. Our fixed fee for a suitable Part 1 appeal is £399, and we win more than half of the appeals we take on.
Read more about planning appeals in Elmbridge or see our guide to appealing an overbearing or loss-of-light refusal.