House Extensions Regulations


Planning permission

The extension or the addition of your house would not need a planning permission if it responds to the following conditions and requirements:

  • only half of the land, situated near to the “original house” can be covered by other buildings or extensions
  • the extension cannot be higher than the highest point of the roof
  • the single storey rear extensions cannot be extended beyond the rear wall of the original house* with more than 3 metres if it comes to an attached house and with four metres if it comes to detached house
  • if the maximum height of the single-storey rear extension is no more than four metres
  • the one storey extensions must not be built beyond the rear wall of the original house* with more than 3 metres
  • maximum eaves height of the extension of 2 metres within a boundary of three metres
  • the maximum height of eaves and ridge of the extension must not be higher than the existing house
  • all the side extensions must be single storey and no higher than 4 metres and no wider than half of the original house*
  • extensions that are two storey and situated seven metres far from the rear boundary
  • roof pitches of the extensions that more than one storey to match to the existing house
  • no verandas, balconies or raised platforms are allowed
  • the side facing and upper floor windows must be obscure – glazed and each opening must be 1.7m above the floor
  • on the designated lands* you are not allowed to have rear extensions of more than one storey
  • on the designated land no cladding of the exterior is allowed
  • no side extensions are allowed on the designated land

Regulation of other building projects:

Loft Conversions
Fence Installation
Conservatory Construction
Kitchens and Bathroom Refurbishment
Boiler installation and Central Heating

“Original house” refers to the house as it was first built on 1 July 1948 (if it had been constructed before that date) Despite the fact that you may not have built an extension, another owner of the house may have done this.

*Designated land means the national parks and the Broads, the Areas of Outstanding Natural Beauty and all the conservation areas as well as World Heritage sites.

The neighbour consultation scheme

This scheme refers only to extensions that are single storey and that are larger and they are permitted between 30 May 2013 and 30 May 2016 which means that the extensions that are between four and eight metres for detached houses and between three and six metres for all other types of houses, need to pass through the process of receiving a permission

Notification of a proposed Larger Home Extension

This notification can be used as from the householder to inform the local authorities of the plans to build a bigger single storey rare extension, however you need firstly to read the guidance note before completing successfully the notification.

Permitted Development for householders

You are strongly recommended to pay attention and to read carefully the technical guidance document that is done by the Government in order to be acquainted how the rules for house extensions are applicable in your case.

Building regulations

The great part of the extensions of properties need approval under the Building Regulations, however there are some classes of new buildings or extensions that are not required a Building Regulations approval.
There are some elements that will normally need to satisfy the requirements of the Regulations when you decide to build an extension.
They are the following ones:

  • foundations
  • flooring
  • walls below ground level
  • energy efficiency
  • structural opening
  • ventilation

Other additional elements that are usually required to be in a definite condition for the Regulations when building an extension are the following things:

  • doors and windows
  • electrics
  • drainage
  • external walls
  • kitchen and bathrooms
  • roofs
  • internal walls

Another important thing to take into account is that whether the plans for building your extension are in accordance with the The Party Wall etc. Act 1996


The floor needs to meet the following requirements:

  • all the ground floors should be resistant to grand moisture and heat loss (thermal insulation
  • structural support of the contents of the room and of the weight of the floor

Basically there are three types of ground floor construction:

Solid floor

The general way to build a solid floor is to provide a base of hardcore altogether with sand blinding and then to add a layer of concrete on it. To finish it in a precise way you need to add a layer of screed on it. The screed consists of sand and cement and is put over the top of the concrete. Then a suitable damp proof membrane (DPM) need to be provided , as the DPM should be lapped in the external walls and if possible on the internal walls of the floor. The thickness of the parts of the floor depends on the ground and also on the way that they are ordered

The suspended Timber Floor

The suspended timber floor need to be protected against growing of plants and other weeds. This type of ground must have a layer of concrete on it you need to make a ventilated gap which will be at least 150mm between the underside of the timbers and the concrete in order to protect from moisture that could easily gather on the floor. The joists need to be made in a proper size due to their span. You may also need an intermediate wall in order to reduce the span to a minimum.

Suspended concrete floor

This construction of the floor is similar to that of the timber floor above, with the difference that here are used pre-cast concrete planks or small pre-cast concrete beams with concrete blocks that lay between the beams. Here, again, ventilation is a necessity and careful structural calculations need to be made.

Contaminated ground and Radon

In the areas where ground is highly contaminated due to some gases,for instance, they need to be ventilated with a gas membrane that will b required to stop the gases from entering the premises. Such kind of gas is the radon that is commonly found in certain areas in the country.


The foundations are required due to the transmission of the load of the building in a safe way to the ground. That means that all buildings must have appropriate foundations (usually concrete) that normally are of one project to another depending on the specifications of each case.

The foundations may be shallow fill (in this case minimum thickness is provided for transfer the load to the soil) an deep-fill (those ones fill most of the trench)
There are also other types of foundations that could also be used when the conditions of the ground do not make the trench fill practicable. In such cases you should advise a structural engineer or to contact the building control to receive adequate help.

Factors that should be taken into consideration when foundations are concerned are:

Type of the soil:

The type of the soil where the foundations will be made is essential for the following reasons:
1. It needs to be suitable to bear the load of the extensions and of the foundation as some soils possess different bearing capabilities
2. The way in which the foundations reacts to the changes of the moisture (for example during the rainy or drier seasons can make the soil expand or contract. This often happens with some kinds of clay soils and the following changes take place at a certain depth (usually 0,75m) so the foundations need to be put deeper so that they would not be affected by the movements of the ground.

Adjacent structures

When you make the foundations you need to make sure that when you excavate for the foundation, you do not undermine some adjacent structures. Normally you should provide excavation to a depth that corresponds to the same depth of the foundations of the building that is near you. If the excavation takes place around an existing footing, you will need to provide special care – by providing concreting of the foundations in shorter sections in order not to undermine the length of the adjacent structure.


Trees have a great impact as through their root system they will take the moisture from the ground and in that case the ground can easily shrink. The level of shrinking depends on the following factors:
Type of soil – for instance clay soils have the ability to shrink more than other types of soils which could react into damaging of the foundation and it structure
The type and size of the tree – the larger the tree is, the more moisture it will draws from the ground

When there are trees in clay soils the foundations need to be made at a deeper level. An important moment is that if the trees are removed, their moisture will be released gradually into the soil and in some cases this could cause damage of the foundations and structures that are situated near these trees.

Drains and sewers

When the load of the foundation reaches the soil it spreads downwards at an angle that is usually 45 degrees. If there is a drain or sewer that is found at that area, there exists a risk of affecting it by the weight of the foundation. For that reason the excavation of the foundation need to be made to the same depth as the bottom of the deepest part of the sewer or drain.

Size and construction of new building

Normally the foundation will need to support more weight from the two storey building, compared that of a single storey. This plays a great role in the determining of the design in terms of the width and the depth. The width of the foundation could also be defined by the thickness of the wall.

Ground condition

In most of the cases the topsoil is removed and the undisturbed ground is found – this means a ground that has not been built on. The foundation cannot be started until such ground is found.

Landfill sites

Some buildings have been constructed on landfill sites which could require more specific type of foundation. An alternative for this situation can be a “raft” foundation. For further advice you can contact a structural engineer. Due to safety and health reasons, specific care need need to be provided when working in trenches, as there exists a risk of potential collapse which could lead to dangerous injuries.

Walls below the ground level

Depending on the fact whether the foundation of the detached building is shallow-fill or deep-fill, you may need smaller or larger amount of wall construction below the ground level. On these walls, the ground walls will be built later. A main point in the substructure is to make sure that there is suitable support provided. The type of the substructure need to be resistant to frost and to the sulphates to the ground.

The ventilation

Each of the rooms in the house must have appropriate ventilation due to health reasons. Each room requires different amount of ventilation. In case new room has been created and an internal wall is added, the n you should also provide care to make sure that room will be ventilated in the right way.
The main rules for the ventilating of the room are:

Purge – this happens when opening the window and the opening need to have an are of 1/20th of the floor area of the room, except from the cases when it comes to bathroom

Whole Building – this represent a trickle ventilation that can be fixed in to the head of the window framework. The area depends on the type of the room:

  • Bathroom – 4000mm²
  • All other rooms – 800mm²

Mechanical extract fan

For any kitchen, bath, WC or utility room there need to be ensured a mechanical extract fan which will help for the reducing of the condensation and for dealing of unpleasant smells. The performance of the extract fans is normally measured in litres per second in the following way:

  • Utility room – 30l/s
  • Shower/Bath – 15l/s with a 15 minute overrun (this means after the light is switched out)
  • Kitchen – 30l/s if it is situated over the hob and 60l/s if it is found on other place
  • WC – 6l/s with overrun

Energy efficiency

When energy efficiency is concerned, there are many different considerations that need to be taken into account. For example a major point is whether or not an application for Building Regulations approval will be required for some projects.

Solar panels

If you want to put a solar panel in your roof you may need Building Regulations Approval as the condition of the roof which will need to carry the weight of the panel need to be firstly checked. In some cases roof tiles may also need to be removed in order to ensure better location and fixing of the panels.

The internal lights

The fixed lights need to possess provision to be able to receive the benefits of the electric lighting when :

  • the dwelling is extended
  • a new dwelling is created
  • when an existing lighting system is changed due to re-wiring works

The type of the light fitting that would meet the requirements are the fluorescent and compact fluorescent light fittings. One successful way to meet these requirements is to ensure one fitting for every:

  • 25m2 of dwelling floor area (without garages)
  • one per four fixed light fittings

Insulation in a loft

The installation of insulation to the loft area requires to make an application for approval under the building regulations.

Re-cycling water tanks

These tanks are designated to recycle the rainwater that is collected from the roof and the ground and in this way it can be afterwards reused for other purposes. Here, you also need an application under the Building Regulations for checking the new drainage system that runs to the tank


All of the radiators that are installed require a thermostatic radiator valve (TRV) that also needs to be installed. It is recommended to place the TRV on existing radiators

Pipe lagging

You are not required to have Building Regulations Approval in this case.

Structural opening

When the extension is made, an opening is also made into the existing external walls. This could be done by removing French windows or other window openings but If a new opening is made, the remaining wall that is above the new opening needs to be supported by installing some beams. The new beams need to have at least 150mm bearing on every side of the opening. The existing walls may also need to be strengthened by a dense concrete also known as pad stones.

Fire safety

As for the fire safety if the beam is steel it needs to be protected by putting two or more layers of carefully fixed plasterboard – the thickness vary and depends on the different specifications. If an exposed timber beam has been chosen then a calculation is made in order to define the inherent fire resistance that it has. The concrete beams normally have greater fire resistance properties.

Here you can find more information about planning permission and planning regulations.

The following guide should be regarded as an introductory and therefore it doesn’t provide legal information.

You are strongly advised to get in touch with your local planning authority for a complete peace of mind. Make sure that all your doubts, concerning the project are disproved before taking any building actions.