Daylight and Sunlight Assessments in Hounslow

Most of the Hounslow work we see is domestic: rear extensions to the Victorian and Edwardian terraces of Brentford, Chiswick and Isleworth, roof enlargements in the streets around Boston Manor and Osterley, and a steady run of larger home extension prior approval applications where a 5 or 6 metre rear extension sits close to a neighbour's kitchen window. Alongside these come small infill and flatted schemes around Hounslow town centre, Feltham and the Great West Road corridor.

Hounslow tends to ask for a daylight and sunlight report when an extension goes beyond the depth limits in its design codes, or when a neighbour raises concerns about loss of light. Our reports are written to answer that request directly: a BRE 209 assessment of the neighbouring windows and gardens, set against the council's own policy wording, usually within 4–5 working days of receiving the drawings.

Recent daylight and sunlight assessments in Hounslow

117 Whitestile Road, Brentford – part two, part single storey rear extension

A homeowner in Brentford wanted BRE evidence behind their pre-application advice before applying for a part two storey, part single storey rear extension. We assessed the windows and gardens at Nos. 115 and 119 Whitestile Road and at the adjoining property on Boston Manor Road, whose rear garden backs on to the site. When the design was revised ahead of submission, we re-ran the model so that the submitted drawings and the assessment matched exactly.

Hounslow approved the application (P/2026/0227) on 25 March 2026.

291 Boston Manor Road, Brentford – two extension options under the larger home extension route

The owner had two alternative rear extension designs and wanted to know how each would affect the neighbours at Nos. 289 and 293 before choosing. We modelled both options and reported on each, covering the neighbours' rear windows for daylight and sunlight and their gardens for sun on the ground. The option taken forward was a ground floor rear extension 5.00 metres deep, 3.95 metres at its highest point and 2.50 metres to the eaves, under the larger home extension prior approval route.

Hounslow confirmed on 24 November 2025 that prior approval was not required (PA/2025/3032).

What Hounslow planning officers look for

Hounslow determines applications against the Hounslow Local Plan (adopted 2015), read with the London Plan. A replacement plan running to 2041 is in preparation, but the 2015 plan remains the adopted basis for decisions. Its design and amenity policies require new development to protect the living conditions of neighbouring occupiers, including their access to daylight, sunlight, outlook and privacy.

What makes Hounslow unusual is how concrete its householder guidance is. To limit loss of daylight and sunlight to neighbours, the council sets maximum rear extension depths by house type: generally 3.05 metres for terraced houses, 3.65 metres for semi-detached and 4.25 metres for detached. Proposals within those figures are less likely to raise a light objection; proposals beyond them will usually need to justify the impact, and a BRE assessment is the normal way to do that. The guidance now sits within the Character, Sustainability and Design Codes SPD (adopted May 2024), which replaced the earlier Residential Extension Guidelines and brings the borough's expectations on amenity, extension depth and overshadowing into one document.

For the numbers, Hounslow relies on BRE BR 209, Site layout planning for daylight and sunlight (2022 edition). A Hounslow scheme is therefore often judged twice: first against the dimensional limits, then, where warranted, against the BRE metrics of VSC, NSL and APSH. You can read the Local Plan at hounslow.gov.uk/local-plan, the Character, Sustainability and Design Codes SPD at hounslow.gov.uk/planning-policy/character-sustainability-design-codes-spd and the borough's other supplementary documents at hounslow.gov.uk/planning-policy/supplementary-planning-documents-guidance.

When you need an assessment in Hounslow

• A rear extension to a terrace in Brentford, Isleworth or Chiswick that goes beyond the 3.05 metre guideline depth, particularly where the neighbour has a side-facing kitchen or dining window close to the boundary.
• A larger home extension (prior approval) of up to 6 metres where a neighbour has objected, or where you want evidence ready before the 42-day determination period runs.
• Two-storey rear or side extensions to the semi-detached houses of Osterley, Heston and Hanworth, where the first floor element can affect bedroom windows next door.
• Backland and garden-plot houses in Feltham, Hounslow West and Cranford, where the new building sits close to several rear gardens.
• Flats above shops and small infill blocks along the Great West Road, Chiswick High Road and Hounslow High Street, where the council will also want to see internal daylight to the new homes.
• Any application where Hounslow's pre-application advice or validation letter has asked for a daylight and sunlight assessment.

How we work

You send us the proposed drawings and the address; we build a 3D model of the site and its neighbours from the drawings, survey data and aerial imagery, run the BRE tests and send a clear report with the results, plans and a plain-English conclusion. The fee is fixed and agreed up front, and the report usually takes 4–5 working days. If a result falls short of a guideline we say so, and we tell you what change to the design would remove the shortfall. The four tests we run are:

• Vertical Sky Component (VSC) – the amount of sky a neighbouring window can see, before and after.
• No-Sky Line / daylight distribution (NSL) – how far into the neighbour's room daylight reaches.
• Annual Probable Sunlight Hours (APSH) – direct sunlight to windows within 90 degrees of south, over the year and in winter.
• Sun on ground – the share of a garden that receives at least two hours of sun on 21 March.

The detail of each test is on our VSC, NSL and APSH page and in our guide to the BRE guidelines; the full service is described on our daylight and sunlight assessment page.

Frequently asked questions in Hounslow

Does a larger home extension (prior approval) need a daylight report in Hounslow?

Not by default, but the prior approval test is specifically about the effect on neighbours' amenity, and loss of light is the point neighbours most often raise. If an objection comes in, a BRE report lets the officer resolve it on evidence; at 291 Boston Manor Road we had the reports ready before the application went in.

My extension is deeper than Hounslow's 3.05 metre guideline. Is it worth applying?

Often, yes. The depth figures in the SPD are a guide, not a cut-off, and the council's concern is the effect on the neighbour. If the BRE tests show the neighbouring windows stay within the guidelines, a deeper extension can be justified on that evidence.

Can you test more than one design at once?

Yes. Where there are two or three options on the table we model them together and report each, as we did at Boston Manor Road. It is usually cheaper than testing one design now and another later, and you choose with the numbers in front of you.

We also cover neighbouring boroughs; our Richmond upon Thames page describes the work we do across the river.

Get a fixed-fee quote

Send the drawings and the site address through our contact page or use the price calculator for an instant figure. You can also call Nick on 01962 809155 or email nick@sunlightassessments.co.uk.