Balconies Impact on Daylight & Sunlight

Balconies can have a significant impact on how buildings interact with daylight & sunlight. While they often enhance the usability of a residential unit, their design and placement can materially reduce the levels of daylight & sunlight reaching both the interior spaces below and neighbouring properties.

This article explores how balconies affect daylight & sunlight assessments in line with the BRE 209 2022 guidance and what developers, architects, and planning consultants need to consider.

Balconies as Obstructions in Daylight Assessments

According to BRE 209 (2022), balconies and overhangs are classed as obstructions when assessing access to skylight and sunlight. Specifically, they can significantly reduce the Vertical Sky Component (VSC), especially in cases where they overhang windows situated below.

When these features combine with external obstructions such as tall buildings across the street, they can prevent occupants from seeing any part of the sky from inside, resulting in very poor daylight conditions.

As set out in Section 2.1.17 of the BRE guide, “Balconies and overhangs significantly reduce the light entering windows below them… it may be impossible to see the sky from inside, and hence to receive any direct skylight or sunlight at all.”

The effect is even more pronounced in areas with high density or with already narrow sky angles.

Sunlight Impact from Overhangs

When assessing access to sunlight, particularly using the Annual Probable Sunlight Hours (APSH) metric, balconies can block sunlight for substantial portions of the day and year. Section 3.2.11 of BRE 209 highlights that “Balconies and overhangs above an existing window tend to block sunlight, especially in summer above south-facing windows.”

This has two significant implications:

It can result in lower overall APSH for the window below.

It can lead to higher relative impacts when assessing the effect of a proposed new building or extension, even if the proposed structure is relatively modest.

The BRE advises that if a window already has a balcony above, it may be appropriate to run an additional assessment excluding the balcony to demonstrate whether the existing feature - rather than the new proposal - is the primary cause of reduced light levels.

Mitigation Strategies in Design

Given these challenges, the BRE sets out a number of practical design strategies to mitigate the adverse effects of balconies on daylight & sunlight:

Staggering balconies: Ensuring that a balcony does not sit directly above a living room window (BRE 209 Section 2.1.19).

Stepped-back façades: Designing the building so that balconies and access decks are set back to prevent them from overhanging windows (Section 2.1.18).

Transparent or open balcony designs: Using transparent materials or open-railing structures to allow more light through to the space below.

Reconfiguring the room layout: Placing rooms with lower daylight requirements (e.g. bathrooms) beneath balconies where feasible (Section 2.1.19).

Each of these strategies helps maintain or restore daylight and sunlight standards while preserving the amenity value of outdoor spaces.

Balconies in Existing Buildings: Assessment Considerations

When assessing the impact of new development on neighbouring buildings, the presence of balconies on existing windows is a key consideration. BRE 209 Section 2.2.13 provides specific guidance: “Because the balcony cuts out light from the top part of the sky, even a modest obstruction opposite may result in a large relative impact on the VSC, and on the area receiving direct skylight.”

This means that a reduction in VSC or APSH may seem disproportionately large - not because of the new development itself, but due to the presence of the balcony. BRE advises assessors to consider running ‘without balcony’ scenarios to contextualise the real source of light loss. If excluding the balcony results in a much smaller relative loss, this strengthens the case that the balcony contributes significantly.

Implications for Planning Applications

In planning contexts, both developers and local authorities must understand the role that balconies play in shaping daylight and sunlight outcomes.

Key points for consideration include:

Demonstrating that new developments do not materially worsen existing poor conditions where balconies already obstruct light.

Considering whether internal daylighting standards (e.g. BS EN 17037 targets) can still be met in rooms with balconies above.

Using BRE-compliant analysis methods to fairly apportion responsibility for light loss between new development and existing obstructions like balconies.

Ultimately, a balcony can affect both the baseline light conditions and the extent to which a new development is deemed to have an impact.

The design of balconies themselves is therefore a material consideration during both the design and assessment phases.

Key Takeaways

Balconies can significantly impact access to daylight & sunlight, particularly where there are other nearby obstructions.

Staggered or set-back balconies and glazed designs can mitigate their effects.

Balconies should be considered in both the design of new buildings and the assessment of impacts on existing ones.

Running comparative assessments with and without balconies is recommended where disproportionate loss is shown.

All assessments should follow BRE 209 (2022) guidance and BS EN 17037 standards.

Need Help Navigating Balconies Impact on Daylight & Sunlight?

At Anstey Horne, we specialise in delivering clear, accurate, and robust daylight & sunlight assessments for planning applications and appeals. If you’re dealing with a complex site or want to understand how balconies could affect your development, get in touch with us today.

For more advice on how we can help support a planning application with a daylight & sunlight assessments please give us a call. If you would rather we contacted you please fill in our Contact Form and we will be in touch.

For more information on all aspects of Daylight & Sunlight Assessments for planning see the collection of articles on our blog page.

For further advice on Daylight & Sunlight for planning, please call our Daylight & Sunlight Enquiry Line on 020 4534 3138.

If you’d like us to call you, please fill in our Contact Us form and we will call you back.