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House Extensions 

house extension 1A house extension is an addition or extensions to your house, in order to increase its size. You can have a one storey or two story extension depending on your requirements. Please see our gallery pics for more information. 

Planning Permission

Depending on the scale of the extension, determines whether or not you will need to seek planning permission. The Government regulations state that you can extend your property, without the need for planning permission, providing that you do not cover more than half of the area of land around the original house. The original house means as it was first built, which means how your property stood on the 1st July 1948. Be aware that any extensions installed by the previous owners of your property count towards the total allowance for your property. Therefore, make sure you do your research beforehand. Read more helpful planning information for house extensions.

Please be aware that your extensions MUST NOT be any further forward than the principal elevation of the house (the front of the house). It must also not exceed the side of the house if this is the side which fronts the road. See various types of extensions.

Terraced houses 

For a terraced house, a single storey or more than one storey extension can go a maximum of 3 metres beyond the back wall of the original house. With regards to a loft conversion, the government regulations state that this type of conversion can have a maximum volume of 40 cubic metres, without the need for planning permission.
Semi detached Houses

For a detached house, a single storey or more than one storey rear extension can go a maximum of 3 metres beyond the back wall of the original house. This type ofhouse extension 2 extension can have a maximum height of 4 metres.
Unlike a loft conversion for a terraced house, which can only have a maximum volume of 40 cubic metres, a loft conversion for a semi detached house can have a maximum volume of 50 cubic metres. Again, you will need to research to see if the previous owners of the property extended the property, as this all counts towards the total allowance for your property. 

Detached houses 

With a detached house, a single storey extension at the back of the house cannot exceed 4m beyond the rear wall of the original house and have a maximum height of 4 metres; if the extension is more than one storey, then the maximum distance is slightly less at 3 metres.  
Similar to a semi detached house, a loft conversion for a detached house cannot have a volume any greater than 50 cubic metres. (The alterations made by the previous owners will also count towards this as well) 

Employing an Architect

When deciding on the design of your extension, be sure to use the assistance of an architect. Some people decide not to use an architect, in order to reduce the overall expenditure. However, by going straight to the builder could mean that you end up with a design that is not suitable for your property, which could greatly reduce the value of your property, if you decide to sell. Therefore, it is always best to seek the help of an architect, because they will be able to design an extension, which will be suitable for your property, which will then increase its value. 
If you are worried about the cost of using an architect, then give them an outline of your budget, so that they can come up with a design that is suitable for you.


Generally, the rule of thumb is to set aside £150 per sq ft of development. Remember though that this is a minimum price, which may vary from company to company. Also, depending on the quality of your fittings and fixtures, determines the price per sq ft. If you decide to use cheaper fixtures and fittings, then you could possibly reduce the cost to £100 per sq ft, but if you opt for more expensive ones then the price could increase to £200 per sq ft.
With regard to the total expenditure, be sure to consider the cost of an architect, engineer, builder’s fees, government VAT, building control and planning costs, as well as the building budget. Therefore, be sure to set aside enough to cover all the costs, so that your extensions are suitable for you and of a good quality.  Finally, be sure that you do not forget to set aside a contingency fund of 10 % for unforeseen circumstances. 


Timescale varies between different projects. The larger the scale of the project, the greater the timescale will be. However, based on a typical house extension, you should be willing to allow 6 months to complete the project, but again this may be shorter or longer depending on the size of your extension and the complexity of it. 
Types of Extensions:


If you only want a small extension, then a porch would be the most suitable for you. However, they can still be built on quite a large scale, but typically a porch is a much smaller extension.  Porches tend to be simple structures of brick dwarf walls and columns, windows and a door, which are either built at the front or rear of the house, but some, can be built to the sides as well. They can be either plastered or left as just simply a bare brick wall, depending on your preferences and budget.
Typically, the majority of porches will not require the need for planning permission. However, some will require this, so you will need to refer to Government regulations before beginning the project.  Generally, if the porch is separated from the house by an internal door, is not heated, so it will not require building regulations certification. However, if you have electrics you must use Part P registered electrician or have the job inspected by the building control department and pay their fee.
The typical cost for this type of extension starts from around £2,500, but bear in mind that this is just a minimum price and this will vary depending on the complexity and scale of the design.


This again is a fairly simple type of extension that can cost anything from £4,000. However, the complexity of the structure determines the cost. A fairly simple structure, can be made from UPVC, timber or aluminium. 
Just like a porch, planning permission is not always required, but certain conservatories may need it. The same building controls for porches apply here also. 

Single storey extension

This type of extension is where the extension is built onto a particular part of the house whereby a single side of the extension is adjoined to the property.
When designing a single storey extension, the following factors need to be considered:

  • The size of the extension
  • The impact it will have on neighbours
  • How the roof will work with the original building and if the material used for the roof is the same covering as is on the existing property
  • Positions of flues, drains and excavations must all be considered
  • Depending on the circumstances, depends on whether or not planning permission will be required. However, building control permission will most definitely be needed. 

The typical cost for this type of extension can start from around £8,000 - £10,000

Multi-storey extensions 

This type of extension is more complex than a single storey one, and this is reflected in the cost. Typical costs can start at around £25,000. Just as in a single storey extension, a multi storey extension can be built to any part of the existing property. However, the impact on neighbours is much greater, because the extension is more complex. These types of extensions almost certainly will require the need for planning permission. However, some instances may not, but none the less it would be wise to get a letter from the planning department to cover this.
No matter what type of extension you decide to have, the installation of one will almost certainly increase the value of your property. However, as would be expected, the larger the scale of the extension, the greater that value will rise.

Here are some of the step processes, and stages to complete a standard house extension.


  • Set out correctly as per the architects drawings
  • Install Re-bar if required
  • Bridge or move any drainage
  • Pour correct concrete mix level and set

Walls Up

  • Lay damp course in brick, or concrete blocks
  • Build inner and outer skin in breeze block using wall ties and insulate with cavity slabs
  • Install catnic or appropriate lintels for finishes
  • Damp proof membrane to be laid on floor using either heavy gauge plastic sheet folded slightly up the walls to meet damp course, or liquid damp proof can be applied
  • Insulate with Celotex and screed over the top of chicken wire

Roof On

  • Install a timber wall plate on the inner skin
  • Joist out the roof with noggins at no less than 1200mm spacing’s between
  • Lay 75mm to 0 Firring pieces to the top of joists
  • Cross batten on top of firings at 300mm spacing’s to take plywood
  • Insulate the roof
  • Install facials, soffits and gutters
  • Rain water down pipes to go into existing drainage, or a soak away if is required
  • Rubber roof to be installed

Complete Plastering

  • Insure all electrics and plumbing is first fixed
  • Plasterboard all walls and ceilings
  • Float and set any surfaces that cannot be plaster boarded
  • Walls plastered with finish plaster

Extension Completion

  • All snags and job completed fully
  • Job must be compliant to the building regulations for completion

Essex Rooms are able to build all types of house extensions. Why not get your quote today from one of our master engineers, you can call us on 0844 448 0400.