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London House Extensions

Building house extension in London: How much does it cost?

Feeling cramped in your house and would like to open and create space? Having build number of 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?
 House extension in Hackney
Even after years of estimating residential projects I still find it hard to give figure to cover all instances. However in short: typical terraced house extension shell in London 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:
  • 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. However we 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 house extension in London: What are the legal hurdles?


Planning permission and permitted development
First of all 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 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 
You have to inform the neighbours of your plans. If you are on a good terms 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.
Building Control
Building Control will have to be notified and 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. Building Control officers usually call on site at certain stages to check. 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 are intertwined as having well defined scope of works will help both calculate accurate costing and have less variables during construction.

Building house extension in London: 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. However 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 that is 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- This is basically the list of fittings to be installed. My advice do the detailed list and present it before 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- It shows when task must be started and completed by. It will help you gauge the progress and might indicate when 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 what costs are fixed and which ones can vary. And 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 this example of extensions in Projects gallery: Extension in Finchley

Please check this example of extensions in Projects gallery: Extension in Catford

Please check this example of extensions in Projects gallery: Extension in Peckham