Planning Objections and overshadowing

When it comes to residential development or extensions, planning objections often hinge on the impact of the proposed structure on the availability of natural light to neighbouring properties. This is a concern grounded in both quality of life and property value. But how do we objectively measure such impact? This is where the Building Research Establishment (BRE) comes in, offering various indicators centred around skylight and sunlight. In a British context, where skylight often outweighs sunlight due to our cloudier skies, these indicators become particularly relevant.

Understanding Skylight and Sunlight in planning objections

Skylight and sunlight are the two components of daylight that shape our experience of natural light. Skylight, or diffuse skylight, permeates the environment even on cloudy days. Sunlight, on the other hand, is direct light from the sun on clear days. The BRE defines daylight as a combination of both and posits that any obstructing structure can impair the “quantity and quality of daylight” based on its size and distance from existing structures. This brings us to the crux of many planning objections: overshadowing.

Indicators for Measuring Skylight

The 25-Degree Line

The 25-degree line is particularly relevant when new developments are directly facing existing windows. According to this indicator, if a new building breaches a perpendicular line at a 25-degree angle above the horizontal from a point 2 metres above the ground level of an existing house, overshadowing is likely to occur. Interestingly, this guideline is not universally embraced; it appears in only a minority of local planning authorities’ householder design guides.

The 45-Degree Line

More commonly found in local planning authorities’ design guides, the 45-degree line indicator is applied to new developments at right angles to existing windows. The line is drawn from the top corner of the proposed extension towards the nearest existing window. If this line crosses the centre point of that window, overshadowing is expected.

The 43-Degree Indicator

This less common indicator focuses on developments close to a boundary line, aiming to prevent any adverse impact on potential future developments on the other side of the boundary. It operates similarly to the 25-degree line but takes a point 2 metres above ground level on the boundary as its base.

Sunlight Indicators

Sunlight often garners more attention from householders as they are more likely to notice a loss of direct sunlight. BRE recommends the 25-degree line for windows oriented within 90 degrees of due south. Another rule suggests that no more than 40% of any private garden should be devoid of sunlight at the equinox. BRE even recommends shadow plans, complex as they are, for assessing large buildings’ impacts on adjoining gardens.

Flexibility and Planning Objections

BRE guidelines are just that—guidelines. They aren’t set in stone but are meant to act as indicators for potential overshadowing issues. Flexibility is often required in their interpretation. For example, if an extension is situated next to a larger structure that already blocks daylight, the indicators may need to be adjusted. This highlights that while they offer valuable guidance, they are not absolute determinants in planning objections.

Planning objections, therefore, often boil down to a more complex interplay of these indicators, existing structures, and future developments. Understanding the BRE guidelines is invaluable for anyone involved in a planning objection based on overshadowing, but remember, they are starting points for discussions rather than definitive answers.

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