A Lymm extension has won planning permission on appeal even though it crosses the council’s 45-degree guideline for protecting neighbours. Inspector J D Westbrook allowed the single-storey rear addition at Chaise Meadow, Warrington, on 15th October 2026, after finding that its particular design and position would avoid harmful overshadowing or loss of outlook.
Warrington Borough Council had refused the proposal because of its effect on the house next door. The appeal concerns a rear lean-to extension projecting about 2.5 metres, rather than a large new building or a change in the use of the property.
I would pay attention to the explanation behind this result. A line drawn on a plan can highlight a potential problem, but here the Inspector also examined the roof’s height, the direction the houses face and the open views available to the neighbour. Those details explain why the appeal succeeded.
Why the Lymm extension crossed the guideline
The approved Lymm extension would run across the rear elevation of a detached brick house. It would have a mono-pitch roof, meaning a roof sloping in one direction, with a maximum height of 3.5 metres and eaves at 2.4 metres. Materials must match the existing dwelling.
The relationship between the two houses was important. The appeal property sits further back in its plot than its eastern neighbour, with around three metres of its side wall already projecting beyond the neighbour’s rear elevation. A roughly two-metre fence divides the gardens, and the gap between the houses appeared to the Inspector to be about one metre.
The Lymm extension would cross the 45-degree line taken from the middle of the neighbour’s broad rear patio doors and windows by a little under two metres. However, the part crossing that line would reduce in height as the lean-to roof slopes away from the house. It would also stand a little under a metre from the boundary.
Actual light and outlook carried the argument
The council’s local guidance uses a 45-degree code to help protect neighbours against overshadowing and obstruction from large extensions near boundaries. The decision records that most properties can extend up to three metres from the original rear elevation at ground-floor level without unacceptable effects, while requiring each case to be considered on its merits.
That qualification mattered here. The existing projecting side wall lies to the west of the neighbouring house. The Inspector found that it did not significantly affect light to the wide rear doors and windows for most of the day. The extension’s position, limited height and depth, and separation from the neighbouring house would likewise produce negligible additional impact.
The neighbour’s outlook was mainly south and south-west, across a long garden with largely uninterrupted views. Against that setting, the limited scale and design of the Lymm extension would have little or no significant effect on the overall view from the rear of the house.
Westbrook expressly acknowledged the crossing of the guideline, but found that the proposal “would not be harmful to the living conditions” of the neighbouring occupiers through overshadowing and outlook. The decision concluded that there was no conflict with local policy ENV 8 or the council’s house-extension guidance.
Permission includes gas protection requirements
There is another practical part of this permission which could be missed if the story is reduced to the 45-degree point. The Inspector understood from the available information that the estate was on land designated as potentially contaminated, and that the original development had included remediation and gas protection measures.
The officer’s report recommended a condition to address those circumstances. The Lymm extension permission therefore requires specified gas-resistant construction measures, including a taped and sealed membrane, a ventilated sub-floor void and sealed service penetrations. The exact specification is in condition 4 of the decision.
I would check that condition with the people designing and building the extension before work starts. Planning permission has been granted, but the safeguards are part of what has been approved. The appeal does not establish that contamination can be ignored simply because the proposed addition is small.
The other conditions require development to begin within three years, compliance with four listed drawings and matching external materials. The complete official decision contains those requirements and the Inspector’s reasoning. The application reference is 2026/00564/FULH and the appeal reference is 6013873.
What another householder can take from the result
For anyone considering a Lymm extension, this is a useful example of why an accurate site drawing and a clear explanation of neighbouring windows matter. The successful argument depended on the real relationship between these houses, including their staggered positions and the openness beyond the neighbour’s rear windows.
It is not a finding that every proposal crossing a 45-degree line should be approved. A taller roof, a closer boundary position or a different orientation could produce a materially different effect. Equally, drawing the line is only one part of understanding the evidence that a particular council’s guidance asks for.
Our house extension guidance explains the separate permitted development route. This decision grants planning permission for the scheme before the Inspector; it does not decide that the same works could have proceeded without an application.
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