architectural services

"THE 45-DEGREE RULE" Sunlight, Daylight And Your Proposed Extension

What is the 45-Degree rule?

The 45-degree rule also known as the 45-degree code and 45-degree guide is a method used by Local planning authorities to measure the impact from a proposal on sunlight and daylight to neighbouring properties.

If you’re planning on building an extension, have you considered its impact on your neighbours? When planning authorities receive an application to develop a property one of the things they will consider is the effect of the proposal on neighboring properties. This includes natural sunlight and daylight.

So before we continue, what do we need to know about the sun:

  • The sun rises in the East and sets in the West
  • The Sun is due South at noon
  • The Sun is also at its maximum height around noon
  • The sun is lower during winter months with shorter days
  • The sun is higher during the summer months making our days longer
  • Direct sunlight is brighter than ambient daylight
  • Daylight is the natural light created between dawn and dusk

It’s your local authorities responsibility when considering an application to safeguard the neighbouring properties amenities.

When designing an extension we need to consider the level of sunlight and daylight currently enjoined by the neighboring properties. Some extensions can be poorly designed and sited, resulting in shadowing that can adversely affect the amenities to your neighbours main inhabited rooms to unacceptable levels.

Rooms such as bathrooms, halls, utilities and landings/stairs are not generally considered and overshadowing to garden areas rarely constitute sufficient grounds to justify a planning refusal.

Protecting existing daylight

Extensions and new buildings should be designed to minimize shadowing on to neighboring properties.

Factors effecting shadowing:

  • Height of the proposed development
  • Size of the plot
  • Building orientation
  • Distance from boundary
  • Topography

Your local planning authority will generally follow BRE guidelines and apply the “45-degree guide” in cases where a proposed development may affect neighboring properties.

The purpose of the 45-degree guide is to make sure the proposal does not take away too much daylight. It is based on the notion that it is reasonable to expect a certain level of light and unobstructed view from a habitable room window.

There are two methods used for applying 45-degree rule.

Method 1: Considers the depth and width of the extension.

Method 2: Considers the height of the extension.

If the proposed extension breaks one of the 45-degree splay lines you local authority may view your proposal as unacceptable.

To make these methods more clear please see the diagrams below.

Method 1:

In method 1 we mark the centre point of the neighbours nearest window and draw a 45-degree splay line towards the proposed extension.

45degree bev 1a.png


Example A is to the left and B is to right.

In example A the extension is reduced in depth where it is located outside of the 45-degree splay. This would normally be considered an acceptable development.

In example B the extension depth is too much and the new proposal falls within the 45-degree splay. This would normally be considered unacceptable.


Method 2:

In Method 2 we mark the centre point from the middle of the nearest habitable ground floor window of your neighbouring properties. From this point we draw our 45-degree splay line out towards the proposed extension.



Example A is to the left and B is to right.

In example A the proposed extension height is located outside the 45-degree splay line. This would normally be considered acceptable.

In example B the proposed extension height is too great and falls within the 45-degree splay. This would normally be considered unacceptable.


Developments under Permitted Development?

The 45-dregree rule does not apply to Permitted Development legislation.


20 Top Architects In Southampton (Architects and Architectural Services)

architects southampton

We are fortunate in Southampton to have a plethora of practices providing Architectural services. With that said we have done our online research and would like to provide 20 popular and reputable architects in Southampton based on the popularity of our searches. We’re 100% sure that in this list there is an architectural practice providing the service you require.

To stop the list becoming over whelming in information we have bullet pointed 3 or more of the services each company provide and have also given a very short description of the first 10 businesses.

Tel: 02381 842389 Web:

To start this list we want to introduce you to We specialize in residential development and cover all aspects from simple house extensions to large new dwellings. We operate in a 40 mile radius of Southampton, predominantly dealing with Southampton, Test Valley, Eastleigh and Winchester borough councils.

•Architectural design •Planning •Permitted development •Building regulations •Certificate of lawfulness •Extensions •Loft conversion •New houses •Alterations •Structural calculations •Sustainable development •Conversions •Change of use •Outline planning


Stride Treglown

Tel: 02380 671991 Web:

Stride Treglown are one of the bigger firms in the area offering a wide array of services for large developments. Stride Treglown’s work also expands past UK boarders to other countries.

•Building surveying •Historic Building Conservation •Town Planning •Landscape Architecture •Environmental Assessment •Architecture


Forum Architecture

Tel: 02380 682095  Web:

This architect practice is based near Ocean village. Forum Architecture was established in 2013.

•Commercial developments •Residential developments •Retail developments •Design consultants •Project architects •Project Architects


Concept Design & Planning

Tel: 02380 331010  Web:

This company helps provide contextual modernism to the area with their designs. The practice shows a great interest in sustainable development.

•Planning applications •Feasibility •Viability •Architectural design •eco-houses •commercial development •Residential development •BREEAM


OB Architecture

Tel: 01962 865344 Web:

This practice is actually in Winchester, but they operate all over the country. OB architectures new home will certainly catch your attentions with their modern style designs.

•Commercial development •Interior Design •Residential development  •contemporary design •sustainable design •Open living



Tel: 02380 388688  Web:

Building Consultancy Bureau are based in Bournemouth as well an office here in Southampton. BCB can cover all works that require the help of surveyors.

•surveys •commercial and Residential •building surveyors •Planning consultants  •Structural Engineers •Building defects •Party wall surveyors • Insurance claims •RICS •ISVA


Pope Priestly Architects

Tel: 02380 335228  Web:

Pope Priestly have been providing architecture work in the area for over 20 years, they cover most fields of development.

•Residential development •Retirement development •Commercial development •Leisure development •Office development• RIBA competitors


Owen Davies Architects

Tel: 01489 589923  Web:

Owen Davies practice provides extensive architectural experience. This includes work in the defense sector.

•Residential development •Refurbishments •Retail Leisure •Industrial development •Commercial development •educational development


Studio Four Architects

Tel: 02380 228923  Web:

Studio Four have offices in Southampton, Winchester and Romsey. They are a reputable company with great working knowledge of the surrounding areas.

•Residential development •Listed Building •Primary Healthcare •Commercial development •CDM regulations •Heritage •Conservation


ADP Architects

Tel: 0845 3651475  Web:

ADP has been practicing for 30 years. The firm is Southampton based and operates across the south region. They work with national developers, house builders and other clients such as the ministry of defense and are a medium size practice.

•Commerical development •Residential Development •Mixed Use •Leisure Developments •RIBA •arb


Graham Ash Architects

Tel: 02380 641811  Web:

•Commercial buildings •Residential planning •Planning appeals


Derek Phillips architects

Tel: 01489 780211  Web:

•Residential •Retail and commercial •Churches


LA Hally Architect

Tel: 02380 616698  Web:

•Contemporary design •Open space living •Listed Buildings


Access Architects

Tel: 02380 769736  Web:

•Commercial •Domestic •Conservation and listed buildings


JAGS Archtechs

Tel: 02380 767284  Web:

•Architectural Design •Building surveys •Rural and historical buildings


AWD Design

Tel: 02380 841231  Web:

•New dwellings •Structural design •Extensions


Architectural Verve

Tel: 02380 420839  Web

•Design services •Design concepts •Feasibility studies


Sanders Design Service

Tel: 02380 207195  Web:

•Architectural design •Planning •Building regulations


Architectural Homepage

Tel: 02380 436096  Web:

•Architectural design •Planning •Small commercial development


Graham Barker Design

Tel: 02380 740392  Web:

•Planning •Building regulations •Architectural design


MDT Design

Tel: 02380 693924  Web:

•Architectural design •Alterations •Building regulations



Tel: 02380 436096 Web:

•Commercial and Residential •Architectural design •Leasehold plans


IHD Architectural Services

Tel: 02381 780950  Web:

•Planning •Architectural design •Alterations •Certificate of lawfulness


Architecture & Planning Southampton

Tel: 02380 222269  Web:

•Conversions •Licensing •Building Regulations


Thank you for using this list. We have kept in mind an array of possible development options. We have also kept in mind development sizes, as well as those searching value for money for smaller residential building work.

Whatever you’re looking for, whether that may be large commercial development or that little bit more space in your home, there is a company here for you.


• Southampton Architects • Architectural services Southampton • Best Architect Southampton • Hampshire Architects • Architectural services Hampshire 

Looking for property investments? Have you checked out property auctions?


Fox and Sons auctions are your local property auction specialists. If you're interested in investment properties, auctions are a must to keep an eye on.

Some of these properties will have scope for further development such as extensions etc. We can provide all you architectural service needs, making your investment property worth that little bit extra.

You can view their auction catalogues at 

You can see us on page 24 of the auction catalogue.