permitted development

"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.


Garage conversions? Convert your garage to a living space

Do you still park your car in your garage? We've lost count of how many homes we've visited with garages, it's a lot. Out of all those garages the total number that actually had vehicles parked in them was two, yes two! One had a vintage car under a old dusty blanket and the other had a quad bike. So if you do actually use your garage for parking your car, in our opinion you're in the minority.

What if you could make efficient use of your garage and convert it to extra living space? Which could also make pretty good financial sense too. Garage conversions that have been converted to high standards could increase your property value by 10%-12% and that's quite a substantial increase.

So you may now be wondering, do you need planning permission to convert your garage?

Firstly we advise you to check whether you have permitted development rights for your house and that there are no restrictions on the garage when it was originally granted planning permission preventing other uses. If you do not have permitted development rights, you will automatically need to apply for planning permission for your proposed changes.

If you do have permitted development rights and want to convert an integral/attached garage, then as long as the work is internal and does not involve enlarging the building, you will not usually require planning permission.

If your garage is detached from the house it may not require planning permission if the proposed conversion is to be used 'incidental' to the enjoyment of the main house. However if the conversion involves the installation of a kitchen, bathroom or sleeping accommodation then your conversion may require 'change of use' planning permission to convert the building to habitable rooms, due to the greater degree of independence from the main house.

So, planning to convert a detached garage to an annexe under permitted development could be possible if it's only to be occupied by guests or dependents of the main house. However, if you want to let it out, you will have to obtain planning permission for independent use. Our advice here is to seek help as this can seem like a grey area and internet research can leave you even more confused about whether you need planning permission or not. 

The issue here is the potential for the garage to become a self contained unit as a dwelling house is only considered as one planning unit. So now the converted garage becomes an 'ancillary' use rather than an 'incidental' use. In simple terms ancillary use would mean it could possibly be used as a standard house (separate unit), where as if the use was incidental it could not exist without the main house. In this case you would likely require planning permission.

In both situations if you intend to develop within your permitted development rights, we would advise applying for a certificate of lawful development (CLD) for the proposed use. A CLD will mean you'll receive a legally binding decision as to whether a proposed development is lawful and doesn't require planning permission.

Building Regulations:

In most instances you will require building regulations to bring your garage conversion up to date with building regulations. Each garage will be different and require different works to bring the building up to standard, such as moisture proofing, insulation, fireproofing, means of escape, ventilation and structural soundness. An inspector will want to check your project as its constructed and will issue you with a completion certificate when satisfied with the finished conversion.

We hope this helps answer your questions with regards to converting your garage. As always if we can be of any further assistance then please get in touch or email us at

Do I need planning permission for a shed or garden room?

summer house_1.png

Lately we are getting a lot of questions about planning permissions and permitted development rights. One of the most popular planning permission queries are shed’s (outbuildings).

A shed or garden room will come under the subject of outbuildings and it’s easier to discuss this topic that way.  An ancillary outbuilding could be a garage, summer house, garden office, pool house, kennel, garden studio, home gym or a storage room (shed). So if you are thinking about adding any of these to home, you will need to assess whether you need to gain planning permission or not.

If you are already thinking about adding an outbuilding, you probably have an idea of the size of the building in mind and what you want to use it for. If you have permitted development rights on your property, we can now move forwards and check if your proposed building falls within those rights. If so, then the good news is you will not require planning permission for your proposed outbuilding.

shed permitted development

Keeping your proposed building in mind. Does it conform with the following?

  • Outbuildings on land in front of the principal elevation require planning permission and do not come under permitted development.
  • Outbuildings and garages are to be single storey.
  • Maximum eaves height of 2.5 metres.
  • Maximum overall ridge height of 4 metres for a dual pitched roof.
  • Maximum overall height of 3 metres for any other roof.
  • Maximum height of 2.5 metres in the case of a building, or container within 2 metres of a boundary of the curtilage of the house.
  • Decking and raised platforms are permitted development, but must not exceed a maximum height of 300mm.
  • Balconies, verandas or raised platforms are not included under permitted development rules and require planning permission.
  • No more than half (50%) the total area of land around the "original house"* would be covered by additions or other buildings.  (This includes extensions.)
  • In places such as National Parks, the Broads, (AONB) and World Heritage Sites, there are additional constraints. The maximum area to be covered by buildings, enclosures, containers and pools more than 20 metres from house are to be limited to 10 square metres.
  • On designated land* buildings, containers and enclosures at the side of properties do not come under permitted development rights and will require planning permission.
  • A proposed outbuilding within the curtilage of a listed building will require planning permission.
  • New buildings that are separate, self-contained, living accommodation or have TV antennas do not come under permitted development rights and require planning permission.

*The term "original house" means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date). 

If you can comply with the above for your proposed outbuilding, it is now important to understand whether or not your property has permitted development rights. Permitted development rights apply to houses but do not include flats, maisonettes or other buildings.

Why is it important for you to check that your house has these rights?

It is possible that permitted development rights have been removed by the local authority by “Article 4 directions”. For this reason we would always advise that you check with your council whether permitted development rights apply to your house.

We also recommend to people that it is good practice to apply for a Certificate of Lawful Development (CLD) when proposing to construct an outbuilding. A Certificate of Lawful Development means you will receive a legally binding decision as to whether your proposed development or alterations is lawful and doesn't require planning permission.

Building Regulations

You may also be exempt from submitting building regulations, this will generally depend on the size of the outbuilding and its type of construction.

So to provide you with some general information to help you comply with Building Regulations when building a new outbuilding within the boundaries of your existing property, such as garages, carports, a summerhouse, sheds or greenhouse you need to consider the following:

Any outbuilding containing sleeping accommodation will require building regulations.

Attached Garages and Carports:

If you are building a new garage that will be attached to the existing home, then you would normally need building regulations approval for the construction. If you are constructing a new attached carport (Carports must be open on at least two sides) then you would not normally require building regulations approval if its floor area is less than 30 square metres.

Detached buildings:

If you are building a detached garage or other outbuildings with a floor area of less than 30 square metres you would also not normally need building regulations approval if:

A)   The floor area of the garage is less than 15 square metres.

B)   The floor area of the detached garage or outbuilding is between 15 square metres and 30 square metres, provided the building is a minimum of 1 metre from any boundary, OR it is constructed from substantially non-combustible materials.

We hope this helps answer your questions with regards to outbuildings for your property. As always if we can be of any further assistance then please get in touch or email us at