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2 storey extension and extensive alterations renovation



Single storey extension



Extension and renovation






If you are located in and around Peterborough you can benefit from our Award winning building service.

Many years of experience, amazing quality of service, huge portfolio of proven work backed up with 'Trustmark' accreditation, and complete customer satisfaction make us the number 1 choice for your building needs in Peterborough


We understand how confusing the whole process can be so we are more than happy to talk through initial ideas and give you cost indications without obligation!






Stages of a house extension project:

An extension building project goes through several stages of building, which are broken out below.

Design & planning permission costs:

You may could choose to have an architect or architectural technician draw up plans for us to follow, or we can design and build your extension. Architectural drawings may come in around £500 to £1,000 for a basic extension or maybe as much as £4k for the bigger projects, depending on the scale and complexity of the work - for more information, call or email for more information.

Planning permission is not always necessary for an extension project, but in some cases you may need permission from your local authority, which can be around £200 depending on your circumstances, such as if you live in a conservation area. Check out our guide on planning permission.


Building regulations are the standards to which all construction projects must adhere and are essential for all building projects in the UK. Building Regulations are designed to ensure buildings are safe, structurally sound, and water and energy efficient. The cost will vary depending on the size of the build and the type of work being carried out, but will typically be between £300 and £500.



The preparing of the site and digging of foundations is

essential to making sure the extension is built safely and

with structural integrity. This phase is the most likely to

bring surprise costs!  if there are complications at this

stage, such as having to move drains or deal with tree

roots, it can slow down the process and increase the cost.


The Shell:


This is where the main building takes place, building the basic structure with either brick and block or a timber frame. A roof is built, and interior elements such as plasterboard and a sub-floor are added to ensure a watertight structure. Costs here are typically related to the size of the build. Nowadays, both brick and block-work or timber frame extensions are at a similar price point, so while they may have various advantages and drawbacks in certain situations, the main building material choice, unless stone, should not be too much of a cost consideration for the average extension job.


Second Fix:


Fitting out the extension with features like skirting boards, doors, electrical sockets and switches, as well as necessities like radiators. The costs of all of these will depend on whether you want to purchase high-end materials or not. Sliding or bi-fold doors can cost thousands of pounds per metre, while simple French doors will cost much less.




There is no limit to what you can spend when finishing the extension - every individual element will have a very different cost, from cheap carpet that is a few pounds per square metre, to imported marble tiles that will costs hundreds of pounds to cover the same space. Costs will also increase significantly if you are adding a new kitchen or bathroom to the extended space. As a benchmark, a new kitchen could cost between £7,000 and £25,000, while a bathroom could cost between £3,000 and £10,000.


How long do home extensions take to complete?


The length of time it takes to build an extension will obviously depend on the scale of the build, without even including any time spent drawing up plans and obtaining planning permission (which can take several months in and of themselves). A rough time-frame would be between three and four months, from the start of the project - clearing the space and digging the foundations, adding the finishing touches, and dealing with any snags you encounter. Delays are common to the start dates, and are often due to clients adding more or changing their minds, work we don’t leave a job until its practical completion,


How do different home extension types vary in cost?


While a building an extension shell relatively is easy to cost , there are a number of different types of extension and options which can have some bearing on the final cost.


Side extension vs rear extension costs:


Whether an extension is to the rear or side of a property will not have a large impact on the overall cost of the build. There will be other factors that affect pricing depending on the design of the extension though, such as how integrated with the original building it is and what structural implications this has, how many windows and doors it has, if a new kitchen or bathroom will be in the extension, or how difficult access is. For example there may be an existing opening that's suitable for the required access to the new building or it may need to be cut into the wall and structural support such as lintels or steels (more likely as the width of opening increases)

Access is an important factor, is there room for the big deliveries required,? the additional vehicles that will be on site during the build, can a digger get to the footings for the dig or will it be a manual job, will the scaffolding fit.

















Double vs single storey extension costs:

While it may seem intuitive that the ground floor is the more labour intensive element because of the groundwork and foundations that must be completed, there are a number of additional costs involved in a second storey that are not applicable to a single storey project. Using scaffolding, working at height, increased structural integration with the original building, changing the roof - all of these factors serve to ultimately balance out the cost.


Masonry vs timber frame extension costs:


Masonry, or “brick and block” construction has been the most common way of home-building in the UK for nearly a century, but timber frame projects are becoming more and more common. Masonry construction sees the structural element built from blocks, with brick or another form of exterior cladding added around it, whereas timber frame uses wood to construct core panels that are assembled on site. Both have benefits and drawbacks in terms of speed of construction and their structural benefits, but in terms of cost, as stated above, the two methods are fairly equivalent.


Bathroom & kitchen extension costs:


The two biggest additional factors that can impact the overall cost of an extension is if you plan to install a kitchen or bathroom in the new space. The price of new kitchens and bathrooms vary widely depending on your requirements and the quality of the products you choose to buy. As mentioned earlier, the  typical price range for fitting a bathroom may range from £3,000 to £10,000, while a kitchen could cost anywhere from £7,000 to more than £25,000. 


Garden room extension costs:


Garden room style extensions tend to be very design-focused, typically single storey with an emphasis on large windows or bi-fold doors that allows the house to flow out into the garden. Although you can still use the basic calculation of price per square metre, there are a number of complicating factors that will impact the final price of a garden room project, such as the materials used and the desired features, such as what kind of doors will be used.

Single storey kitchen extension-GMFBuild
Single storey kitchen extension-GMFBuild


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View our previous projects



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