Wave Dynamics GuidesDaylight, Sunlight and Overshadowing Explained
How daylight, sunlight and overshadowing are assessed for planning in Ireland and the UK using BRE 209 and EN 17037, for new homes and neighbours.
In Short
A daylight and sunlight assessment checks whether new homes will get enough natural light and whether a development will take too much light from neighbouring windows and gardens. In Ireland and the UK it normally follows BRE 209, Site Layout Planning for Daylight and Sunlight, and the European daylight standard EN 17037.
- Two questions: light within the new development, and effects on neighbours.
- Neighbour tests include Vertical Sky Component and annual probable sunlight hours.
- New homes are assessed against EN 17037 daylight targets.
- Overshadowing of gardens and amenity spaces is checked on 21 March.
Why It Matters for Planning
Good daylight makes homes healthier and more pleasant and reduces energy use. Planning authorities in Ireland and the UK expect daylight and sunlight to be assessed for most multi-unit residential schemes and for developments near existing homes. National guidelines on compact settlements and apartments refer to the BRE guidance and EN 17037.
Effects on Neighbours
BRE 209 uses tests such as the Vertical Sky Component (VSC), which measures how much sky a window can see, and no-sky line analysis. For sunlight, annual and winter probable sunlight hours are checked for windows facing within 90 degrees of south. A reduction to less than 0.8 times the former value is generally taken as noticeable.
Light Within the New Development
The 2022 edition of BRE 209 adopted the EN 17037 approach, using either target illuminance or daylight factor across a set share of each room. Bedrooms, living rooms and kitchens have different targets. Sunlight exposure to new homes is also checked.
Overshadowing of Gardens and Open Space
BRE 209 recommends that at least half of a garden or amenity space should receive at least two hours of sunlight on 21 March. Sun-on-ground diagrams show how this changes with the development in place.
Frequently Asked Questions
Is BRE 209 mandatory?
No. It is guidance and is meant to be applied flexibly, but planning authorities rely on it heavily and expect departures to be explained.
Is right to light the same as a daylight assessment?
No. Right to light is a legal property right, while daylight assessments are planning tests. We provide right to light risk assessments separately.
This guide gives general information and is not a substitute for project-specific advice. Requirements change, so always check the current regulations, guidance and your planning conditions. Ask our team about your project.
Jon Maguire (BSc Hons MIOA) brings over 8 years of expertise in acoustic consultancy, specialising in environmental acoustics with a focus on 3D modelling, assessments, and detailed design for industrial, commercial, and energy projects. He has lead noise assessments for key clients while thriving in multidisciplinary environments. Jon’s diplomatic communication skills are ideal for stakeholder consultation.
Jack is a Field Engineer at Wave Dynamics, supporting the delivery of environmental monitoring and acoustic consultancy services through detailed on-site fieldwork. He has hands-on experience in noise monitoring, vibration monitoring, and dust monitoring across a variety of infrastructure, construction, and environmental projects. Jack is involved in the setup, operation, and maintenance of monitoring equipment, ensuring accurate data collection in line with relevant standards and project requirements. He works closely with consultants and project teams, providing reliable field support that underpins high-quality assessments and reporting.
Aidan is the Director for all U.K Operations and has worked in multiple industries including for clients in the UK and internationally operating in the residential, industry, healthcare, education, and construction sectors.
