London Extensions

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8th April 2020

Kieran Morgan, Design Director at Found Associates is a good friend of Christian, the Mr

London Extensions

Kieran Morgan, Design Director at Found Associates is a good friend of Christian,
the Mr and Mrs Clarke partner in Hackney and Haringey as well as an incredible designer.
If you’re thinking about extending your home in the near
future then this is the perfect read for you.

Kieran is really passionate about demystifying the process of renovating
or refurbishing properties. There is so much information about it out there,
but he finds that when people are totally unprepared for what to expect.
We thought it’d be great to share some of Kieran’s expertise & knowledge.
He is the expert after all…

Extension lickey view

How much does it cost to extend my house?

Single storey extension – If you wish to extend the ground floor of your home by way of a side, infill, rear or wraparound extension, the approximate price in London will usually be between £200 and £350 per square foot. 

Two-storey extension – A general rule in the industry to calculate the cost of two-storey extensions is to add 50% to the guideline price of a single storey extension.

Loft extension – If you wish to add a loft extension to your home by way of a dormer, mansard, hip-to-cable, partial or full width extension, the approximate price in London will usually be between £160 and £200 per square foot.

Basement – Due to the structural and construction complexity and risk of forming a basement, this is the costliest form of extension. A new basement in London will typically cost between £400 and £550 per square foot. 

The main benefit of extending your home is that it provides an opportunity for you to adapt the way you live and shape your environment to suit your future ambitions, interests or needs.

Kieran Morgan, Director

Do I need planning permission to extend my house?


Whether you require Planning Permission to extend your house will depend on the type of extension you are seeking to add. Some basic considerations are set out below, but we recommend you seek full advice before you undertake your project.

Single storey extension – These are the most straightforward extensions for which to achieve planning consent. 

Development Rights If your property is a flat, however, planning consent will be required. 

Two-storey extension – Obtaining planning consent is often more complex due to issues such as overlooking neighbouring properties and nearby residents’ rights to light. 

Loft extension – In some instances these are within Permitted Development Rights but if you want to push the boundaries a little, or if your property is a flat, planning consent will be required. 

Basement – If it is exclusively within the footprint of a house, a basement will be within “permitted development rights”. However, if you wish to get natural light into a habitable room, you may need to extend beyond the house, in which case you will require planning consent. 

You can find more planning information here If your property is listed or within a conservation area there will be additional restrictions on your ability to extend.

A typical extension, especially in prime areas of London, can increase a home’s value by 10 to 30%.

What will influence the cost of extending my house?

fond associates

Where your extension falls within this price range will be influenced by the level of specification you want to achieve, and the choice of materials and products you choose, from standard off-the-shelf to high-end bespoke.

Elements to think about are:

  • Exterior finish (e.g. brick, wood, zinc or render)
  • Window and door type (e.g. steel, aluminium or wood, sliding or bi-folding) 
  • Window and door size (e.g. bespoke floor-to-ceiling or standard sizes)
  • Floor finishes (e.g. polished concrete, ceramic tiles or engineered wood)
  • Wall finishes (e.g. fair-faced concrete, pained plaster, exposed brick or blockwork)
  • Kitchen design/supplier (e.g. Italian designer, bespoke handmade or Ikea)
  • Joinery (e.g. Italian designer, bespoke handmade or Ikea)
  • Lighting/electrics/audio visual (e.g. whole-house control, dimming or simple switching)
  • Heating (e.g. air conditioning, underfloor heating or radiators)

Your extension could enable you to have a more sociable kitchen with better connection to your outside space. It could also provide more tailored spaces.

How can Found Associates help?

As architects, Found Associates are often the first point of contact for a project and will provide invaluable initial advice. Through the process of briefing and concept design we can help you to develop your ideas while also navigating potential project risks such as complex planning permission and local authority requirements. Perhaps most importantly, we can help you to turn an idea into reality by producing the tender drawings you require to obtain accurate construction costs.

Throughout the process of concept design, detail design and tender drawings our knowledge from previous projects allows us to provide you with alternative solutions that may be more economical and help reduce costs, focus the works or enable more of your home to be refurbished for the same cost. Sometimes reorganising and improving poor existing spaces can be more effective than simply adding a large extension that is poorly conceived.

Durant Street