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London House Extension

Building London house extension: How much does it cost?

House extension in Hackney

Feeling cramped in your house and would like to open and create space? Having build number of  house extensions we have picked up few things along the way that might help you.  A lot of the times the first question springs up: How much does it cost to build a London house extension?
Even after years of estimating residential projects I still find it hard to give figure to cover all instances. However, in short: typical terraced London house extension shell will cost you £35k upwards subject to vat.
The potential additions (I will only give minimum not exceeding mid budget) inclusive of all building works and all supplies:
  • Bifold doors £2-5k
  • Kitchen £3k to 15k(can be much more for high end)
  • Bathroom £3k - 7k
  • Toilet or utility room £1k - 3k
  • Flooring and skirting £2.5k
  • Lighting and electrics £1k
  • Rooflights £1k
Other things you must plan the budget for before building London house extension
  • Planing permission application, party wall agreement, planning and construction drawings, structural design and building control application £1,5k- 5k (if your project requires hiring Architect you will need a budget for architectural design work)
  • Alterations of existing house subject to scope and size £700-£1500 per m2
  • Landscape and external works subject to scope
These figures are very approximate and I would strongly advice to get an estimate specific to your project.
In order for us - builders to provide you with accurate quote you will need drawings, scope of works and schedule of fittings. But, we will come back to this a bit later in this article as we want to know what are the legal obligations before starting with the construction.

Building London house extension: What are the legal hurdles?


London House Extension planning permission and permitted development
Before starting to build your London house extension you will need planning permission unless it falls under permitted development. The scheme currently is valid until 30th May 2019 allows homowner to extend original house up to 3 meters in case of terraced house and 4 meters if the house is detached.You can build larger London house extension under permitted development subject to neighbour consultation scheme - 4m and 8m respectively. More can be found on planning portal- government website.
If you are willing to build larger extension than permitted development allows you will have to obtain planning permission. Simple set of planing drawings is usually needed to be produced and attached when submitting your application.
Party wall agreement 
Informing your neighbours is an important part. If you are on a good terms with your neighbours - they will give consent. You may have to employ Party wall surveyor. Surveyor takes care of the agreement but you will bear the costs and process takes approximately 6 weeks.
Importance of Building Regulations
It is important to notify building control and pay their fee paid 48 hours prior the works start.
Building Control is entity within local authority (you can get private companies providing the service as well) that ensures the works comply with Building regulations. Regulations describe acceptable standards for structure, insulation, fire, ventilation and other aspects of the building. Approved inspectors usually call on site at certain stages to do the checks. BCO signs off and issues compliance certificate at the end of the work if all is well.
My advice is to have first meeting with BCO at least a week before kick off just to present the project and discuss any regulations that may affect the scope of works.
What do we need to have fixed cost and finally start the works?
These 2 questions intertwined as having well defined scope of works will help both calculate accurate costing and have less variables during construction.

Building London house extension: Finally- lets build it! How to stay on time and on the budget?

Client is keen to start and builder wants to move in, to secure the job. Therefore, before we start it is well worth checking that we have everything we need for the journey:

Scope of works- Well defined scope of works does not have to be multiple pages- actually I prefer it short and concise. It needs to contain the level detail that would allow us (builders) give you fixed quote.

Construction drawings- Not all the drawings are the same. There is a difference between planning drawings and construction drawings. And these construction drawings together with the rest of the specification provide enough information for various trades involved to complete their part of the job.

Schedule of fittings -   Can be defined as a list of fittings to be installed. My advise is  you should do a detailed list and present it before the start.

Procurement- Procurement is simply shopping for specialist items that are outside general builders work scope. It seems like builder should know the cost of Edwardian slim glazed timber sash windows with lamb tongue profiles of various sizes.  But in fact, I would advice to get a quote from specialist supplier for specific product. Suppliers might need visit the site, it will take time and test your negotiation skills . However, for you- the homeowner- it means less surprises on a budget front in a construction phase. So either you do it yourself or allow small contingency for builder to mange things for you.

Programme-  Shows you when the task must start and  when to complete it. Programme will help you to gauge the progress and might indicate when the client's input is required.

Contract- Read and understand the contract you are entering. It describes the relationship between builder, client(employer) and any administering parties Architects, surveyors etc. If not sure of any part do not hesitate to seek for help. Understanding the contract will help you to understand the differences between fixed costs and the ones you can vary. Trust me variations are expensive to client and  headache to the builder when trying to stay on course.

If you have covered all of the above then well done! You are more ready than 90% of our clients when they turn to us with request to start the works.
Do contact us - we will be happy to help!
Andrew Draciovas MD AFL Construction

Please check these examples of London house extension in our Projects gallery:

Back and side extension: Extension in Finchley

Side extension : Extension in Catford

Back extension : Extension in Peckham