House Extensions and Planning Permission

Local authority planning consent is not a must for all house extensions. If your extension is covered by permitted development (PD) rights, you can save time and cost of application.

For instance, a single-storey rear extension could be up to 3m deep for an attached home, or up to 4m for a detached building subject to neighbour consultation scheme. These limits have been stretched to 6m and 8m respectively until May 2016 in the UK.

When you inform your local council about a house extension projects within the permitted development rights, they have to consult owners or occupiers of adjoining properties. (21 days is the minimum consultation period). This is also known as the neighbour consultation scheme. If your neighbours with adjoining properties do not object to your extension project, then the council would not need to investigate your potential project. If there is an objection from one of your neighbours, then the impact of the potential house extension on the adjoining properties would be investigated by the local council.


Ground floor extensions to the rear of houses are not contradictory most of the time while obtaining planning approval. The biggest reason is that the main preoccupation of planners is the impact the alterations to your building would have on nearby neighbours. Therefore, house extensions that involve the first floor and above attract more investigation. However, permitted development rules still allow you to add some extension to the original property without making a planning application.

Permitted development rights do not allow changes in designated lands or listed buildings designated land means the property is located in a conservation area, an area of unmatched beauty, national park or similar protected place. In these places, consent is required.

If you will not need to make an application for planning approval for your extension, you should know that planners’ attitude toward planning permission vary between councils. Therefore, you need to find out the standards of your local authorities, and how sharp they apply them. An architect who has knowledge about the applications of locals is invaluable when it comes to consider general rules of thumb which are applied by the most local authorities while assessing the application. You should take following factors into account while drawing up design. You should also consider 3D models to help. All stakeholders will appreciate the potential of your house extension plans.

Consider the following factors when drawing up a design and also consider 3D models to help all stakeholders really admire the potential of your house extension plans.



If the new additional space in your home presents you a prominent view directly into the garden of your neighbour, or into windows of their home near the boundary, planners will be concerned. The planners will also investigate if significant daylight is lost to the neighbours’ ground-floor windows because of the new section of first floor. In most cases, especially urban and suburban areas, an extension to a house is obligated to have a recognisable effect on its immediate neighbours.

The planners will determine if the effect is significant and “detrimental to the amenity” of the neighbouring buildings. The evaluation could be very subjective. In most cases, neighbours object any development which has an effect on the property. However, the objection of a neighbour does not create grounds for a rejection of planning permission.

In order to help planners make viable decisions, local authorities generally use a combination of “rules of thumb” and written policy. They generally have written into the development policy set distances which has to be achieved between various types of elevation houses. For instance;

● The side of a home may must have 7m between it and a rear elevation of another property

● The fronts of houses may need to at least 22m apart

● A back garden’s minimum depth could be set at about 10m

● In first-floor house extensions to the rear of the house a 45 degree line is drawn on the plan from the corner of your neighbour’s closest ground floor window actress to the back of the garden of your home. If the extension you proposed crosses this line, a rejection is possible.

These rules are generally applied to housing estates. However, they will be effective on the evaluation of applications for house extensions to existing buildings. The main problem in the application of these general rules is that in some situations they are not appropriate or they are not applicable to specific situations. For instance, a steep level change between houses. It could be difficult to make planning officials accept these kinds of variations sometimes.



When planners say “keeping” they do not only demand a new addition matches only the materials of the nearby buildings. They also demand that the addition should match the size, scale and proportion of nearby buildings. If your neighbourhood does not have a dominant architectural style, it would be easier to get consent from your local authorities whether the design is contemporary or discordant.

Planners also tend to approve house extensions which are visible from the road to be subsidiary to existing property.

In force, the ridge height of the new part of the property is expected to be shorter than the main ridge height. It could be difficult to achieve the latter if an extensive addition of floor space is necessary at first floor level. Moreover, it is also illogical if the home could take a better shape by adding something of a similar size which matches the original property. In these kinds of situations, negotiation skills are important.


Terrace effect is also a big “no” for the planners. If your property is located in a typical suburban street, full of rows of semi-detached properties. When all house owners decide to add extensions to their side verges, the street will appear as a terrace of houses. Planners think that this is a bad thing.

Insisting that these extensions step the first floor back from the front face of the property is the best solution for that. Then, the street will appear as a row of terraced homes with the first floors close to the verge stepped in. This is a good thing according to planners. It seems like this rule of thumb is applied vehemently in all parts of the UK. The only difference being the distance that is viewed as an reasonable indent. Some councils are insistent on 2m. Other councils would tolerate 1m. If it is remote enough from the boundary, constructing the extension wall flush with the current front wall could be acceptable.

Especially in older housing estates, it is not unusual that the front faces of the properties are in line with each other. Roads which are less planned also tend to have stretches of properties which are approximately aligned. This is called as “building line” and any type of house extensions which are proposed closer to the road than the houses of the neighbours are evaluated as potential threat to the quality of life. Moreover, it would also be evaluated as a threat to the order and harmony of the neighbourhood. If there is a building line beside the road, and your potential project breaches the road, your application would be rejected.



You have to consider all potential complications whether you must get permission for the extension or not.

● House extensions will always require separate listed building permission if the house is a listed building.

● If your project has a potential to affect the structural integrity of neighbouring houses(for instance, if you're excavating close to a verge or underpinning shared foundations) then you'll have to inform your neighbours of your intentions by serving a notice under the Party Wall Act.

● Permitted development rights are not applicable to listed buildings and properties in conservation areas

● Dating from April 2015 homeowners are responsible for the safety on their building projects – big or small. Thus, all projects require a health and safety plan and homeowners are required to manage that plan.



Yes. All regulations apply to house extensions. However, one or two aspects of house extensions must be noted.


In a standard two-storey property, the regulations stipulate that some of the upstairs windows must be wide and low enough for a person to climb out when there is a fire. The name of these windows is “emergency egress windows”. These kinds of windows are must in all habitable rooms upstairs.

Moreover, if the room does not open to the outside or to the hallway, it is also required for ground floor rooms. A habitable room means a room that a person would likely be in for a long time. Bathrooms are not habitable rooms for example. Most of the standard windows meet these necessities. However, in some cases, the lower window is an inconvenience. For instance, rooms in roof bungalows do not have these kinds of windows. For a three floor house, a fire-escape stairwell is a must. A fire-escape stairwell removes the need of emergency egress windows in other rooms.

The size and location of windows that is close to the boundary, is often limited by the planning departments. Building control officers also have some restrictions. They have restrictions because if your home is on fire, it can also spread between houses through windows close to a shared boundary. Thus, the size and number of windows in an extension wall which is close to the boundary of a house are limited especially if the new wall is closer than 2m.


Another type of regulation which affects windows is about the fresh air requirement in the room. According to the regulation, if the total area of openable windows in a room is at least 20% of the total area, then there is sufficient fresh air in the area. As you can see, there is a potential contradiction between these regulations. One of the regulations limits the size of windows, and the other one requires larger windows. The only solution for that is mechanical ventilation.

A garage is evaluated as a potential fire source because of the fuel tanks of the cars in the garage. Therefore, there should be at least thirty minutes of fire-protection between the garage and the rest of the property. The risk of spilled fuel flowering under doors into the house is also considered by the regulations, and a step up from the garage is required to prevent this kind of situation.



The rules about controlling the amount of energy which is necessary to heat new additions to property are more adjuratory than the days we do not consider global warming as a threat.

Regardless how bad or how well the existing property is insulated, new additions such as roof, walls or floors have to be compatible with today’s standards. If the area of glass minus the area of current openings covered up by the new property work is bigger than %25 of the floor area, a calculation should be made to show that the heat loss from the whole of the house is compatible with the regulations after the extension.

It follows that, if you want to increase the area of glass more than 25% figure, you will be obligated to increase the insulation levels of the new walls, and you may need to add insulation to the current walls, to compensate for the heat lost through the glazing. The required calculations are bit complex and they are generally carried out by a professional.


House extensions would be the perfect way to provide you with what your existing house may lack. However, you need to evaluate your needs and design considerations carefully. Perhaps, the extension will be covered by permitted development (PD) rights, and you can save your time and money without waiting for the planning permission of local authority.

However, do not forget that you will have to adhere to building regulations and stipulations. Thus, do your research and receive advice from professionals. Taking your time and working with a professional architect would be very helpful for you to protect your investment and get in return for your hard work.