House Extensions

House Extensions

House Extensions

Extending your home is a popular way to increase space and add value to your property. With the hassle and costs of moving house – from legal fees to stamp duty – the reasons to stay put and improve your existing home soon mount up.

But where do you start? We have compiled information about House Extensions to help you make an informed decision.

Read all House Extensions posts


House Extensions

Single or Double Storey Rear Extension

House Extensions

Rear Extension

House Extensions

Wrap-around House Extension

House Extensions

Cellar or Basement Extension

House Extensions

Garage Conversion

House Extensions

Loft Conversion

There are few world-class cities where you can own your own house and convert it for your needs, and none as exciting as London. The city’s rich stock of residential housing has great potential for improvement. If you already own property in the capital and can’t justify the costs of moving house, renovating and extending your existing property may be the right move for you. Best of all, you’ll be able to stay in the neighbourhood you know and love.

Strict planning regulations in neighbourhoods rich with heritage housing make house extensions a challenge for some. Seeking the help of an architect, rather than going directly to a standard-issue builder or home-extension specialist, means the specific character of your home will be respected and enhanced. An architect will unlock potential and use materials in an original way that can complement your home’s historic appeal.

Once you’ve found an architect whose style and personality balance your own, the process of transforming your home will fall into place. Together you can collaborate on tailoring the original bones to your personal lifestyle with detailed specifications, starting from the party walls inward. Even if planning regulations are stringent in your neighbourhood, you’ll usually be able to extend outwards at least enough for an extra room or two – taken from wasted outdoor space, eaves in a pitched roof or awkward corners you didn’t even know you had.

You could extend a kitchen to incorporate an eat-in breakfast room, add an en suite bathroom, a bedroom for a new child or a home office. In a neighbourhood with newer housing stock, like a London suburb or brownfield development, more involved home extensions may be possible, like wraparounds incorporating a side return and rear, a second storey, garage topper or double-height rear extension.

House extensions are carried out in a more compassionate way today than they’ve ever been, and a good architect will strive to preserve original architectural elements – like decorative cornicing, ceiling roses, skirting boards, dada rails and picture rails – while giving your home the modern openness so many desire. Pivoting doors and Crittall-style steel windows are brilliant complements to period decorations and antique brick.

Once you’ve committed to the process, a house extension will make additional changes easier and less cumbersome, like new sash windows, flooring or a fresh paint job. They could be done concurrently with the structural work, pull everything together and help you get a good-as-new home that works with your unique way of life.


House Extensions

Building an Extension: A Beginner’s Guide
Read the article at

House Extensions

Extending a house: the ultimate guide for building a house extension
Read the article at

House Extensions

House extension rules made permanent to cut ‘time-consuming red tape’
Read the article at


Scenario is a boutique architecture studio focused on improving homes with spacious, contemporary extension projects across London and beyond. Through our bespoke architecture service, we tackle projects of every scale and complexity, from modest single-storey extensions to side-return extensions project, basement extensions, loft extensions and rear house extensions project.

Our highly skilled architects can take you step-by-step through the challenge of building a house extension. We’ll collaborate closely with you from the initial drawings, detail design and planning, guiding you through the tender and construction process and completing your house extension on time and on budget.

Early adopters of the latest drafting and building technologies, we use innovative 3D design and visualisation tools as a standard for all our house extensions. Our experience has shown that real-time visualisations and virtual reality are extremely efficient tools for choosing finishes, fixtures and fittings, and simulating natural light.

We use 3D building information modelling (BIM) to produce reliable construction information, so all our project data comes from an accurate 3D model. Using this technology collaboratively with consultants and contractors is proven to save our clients time and money. This Chartered Institute of Building case study featuring a Scenario project demonstrates the benefits of this advanced technology for house-extension projects.

Scenario Architecture is a RIBA Chartered Practice. We comply with all the criteria of the Royal Institute of Chartered Architects, covering insurance, health and safety and quality-management systems.

Talk to us about your project

We would love to hear about your project and discuss how we can help

Please use the link below to schedule a call at a convenient time

Select a day


Select a time


Contact Information

Any information you provide us remains strictly confidential


Any information you provide us remains strictly confidential

Ownership status for the project

The property is

Any information you provide us remains strictly confidential

Property type

The project is

Any information you provide us remains strictly confidential (You must select at least one option!)

Aims of the project

Your budget

Any information you provide us remains strictly confidential

Please indicate an estimate of your target budget (excluding VAT and professional fees) so we can advise on the viability of your requirements

Budget range

Additional information

Any information you provide us remains strictly confidential

Please attach files such as plans, estate agent brochures, image and surveys


Nearly any property you purchase in the southeast will retain or accrue value. When and if it turns out you need more living space, you’ll want any enhancements you make to the size of your home to enhance your asset, too.

A good architect will factor in your home’s location, layout, structural integrity and the size of your family to make your project work for you and your budget. A house extension cost shouldn’t cancel out the benefits of a house extension.

Unless your investment is a purpose-built flat, you should be able to gain extra space that suits your lifestyle. If you own just part of a house, you can build up, down or out, depending on your specific location. If you own the entire house, chances are better you can add substantial square metres.

In some neighbourhoods around London, loft extensions and side-return extensions (recouping the side-rear void often left open between terraced houses) are grouped under “permitted development”, which means they sometimes don’t require planning permission from the local council if the final plans heed the extended volume requirements of the area. Avoiding time-consuming planning applications will save you money in the short run.

On the topic of money: it’s always difficult to propose a house extension cost without evaluating the home in question, the resident family and their plans. But it’s likely you can nearly double the size of your home’s original square-metre floor area at a fraction of the cost of the original house. Plus you will, of course, gain a nearly new living space without paying the stamp duty and agents’ fees associated with moving house – although you may need to purchase renovations insurance.

As with most building-related activity, it is wise to source three to five quotes for a house extension. With a range of budgets to hand, you’ll be able to assess which seem low, high and just about right, and choose accordingly. The foundation, walls and roof will soak up about 15% of your costs, followed by Velux and rear glazing.

You’ll want to price fixtures, fittings, appliances and any upgraded materials separately, so as not to be shocked when you receive that last bill – new kitchens are particularly dear, so keep your eyes out for deals and floor sales in the months leading up to a project. Once you’ve agreed on a budget, set up a payment plan with your architect and builders that works for everyone.

The House Extension Cost varies and this will depend on the scale, design, exterior materials and interior finishes of your extension. Before designing an initial concept for our clients, we discuss their big-picture aspirations and daily requirements.

When we budget the House Extension Cost on any home, we must consider the different types of extensions projects. Extending upward with a loft extension, for example, is often significantly cheaper than a side-return extension and rear house extension and most definitely a basement extension.

We understand our clients’ desire to understand the cost of building an extension before committing to the process. For a single-storey extension – be it a side-return extension or rear house extension – we allow between £2,500 and £3,000 per square metre, depending on finishes. These figures can also apply to renovating the existing areas within a house.

Excavating a new basement is a great way to add significant floor space to your house with limited planning regulations. However the House Extension Cost per square metre is, by far, the highest in a basement. We allow between £3,000 and £3,500 per square metre, subject to finishes.


House Extensions

FAQHow long will it take to obtain planning permission for my project?
The standard consideration period for a residential project is eight weeks, this is the official time frame for your local council to carry out consultation with the neighbours and reach a decision.  We recommend allowing for a minimum of ten weeks from submission to decision as in practice the process always takes slightly longer for the following reasons: 
  • The decision period clock only starts ticking once the application is validated by the Council, This requires then to check that the forms are completed correctly and that the submission contains all the necessary drawings, statements and reports.
Validation can take anything from a few days to couple of weeks when the council is very busy, which is most of the time…
  • Although required by law to provide a decision within the statutory eight weeks period, it is not uncommon for councils to miss the deadline of the consideration period, normally only by a few days, sometimes longer. 
While there are some effective measures to apply pressure, which we do not hesitate to use when appropriate, it is generally beneficial for the project to bear with the council a little longer. 
  • In some cases the council may ask us as your agent for an extension of time, this may be requested due to internal reasons or as an acceptable result of a professional discussion that we are conducting with them about certain aspects of the application that they are not sure about.

House Extensions

FAQWhat is pre-planning and will it be required for my project?
Once we have an initial scheme designed for your project which you are happy to proceed with, we will advise whether we recommend obtaining pre-planning advice or proceeding directly to the submission of a full planning application. Most of our projects are submitted first to pre-planning when the following applies.
  • Our experience shows that planning officers respond better to projects when they feel consulted and collaborated with. We find that when we truly listen to their often helpful and valid feedback and treat them as consultants for the projects and not representative of an evil enforcing authority, they tend to collaborate well with us and demonstrate increased flexibility.
  • Although the council in theory have eight weeks to consider your application, in practice they are constantly overloaded. They will only look at your application in the last few days of the consideration period. If this is the first time that they come across a scheme that they were never consulted about, our chance to secure permission for you in a single attempt is significantly compromised.
  • The standard practice is for the council to consider the full planning application as submitted and then issue a yes or no decision. Case officers are not required or even encouraged to enter a discussion with us or accept resubmission of minor changes to the proposed scheme during the consideration period.
In practice our established working relationships and long-standing experience working across Greater London and the Home Counties often enables us to have a meaningful discussion and even introduce minor tweaks to the submitted scheme within the consideration period and prevent the application from being rejected. The chances for this strategy to deliver the desired results increases significantly with projects which were submitted first for a pre-planning advice.

House Extensions

FAQWhat is building control and is it required for my project?
In a nutshell building control is the means by which Local Authorities enforce compliance with current Building Regulations.  In practice there are two main ways to go about obtaining the required advice and certification for your project, via your Local Council’s Building Control Department or via direct appointment of an Approved Inspector who is authorised to carry out the inspection and certification on behalf of any local authority.   The role of either the Council’s Building Control Officer or an Approved Inspector is to verify that your project meets all current Building Regulations. They will review and approve all the drawings, inspect the actual work carried out on site and once the project is completed, issue the final compliance certificate. Due to an open market, healthy competition between local councils and approved inspectors, the process and associated costs are almost identical. Having said that, our experience is that the private inspectors still feel and behave more as your appointed consultants and the council’s service still feels more like a statutory inspection and it is often slower and less responsive.  While it is always good to be informed and understand the process well, as your appointed architects we will take care of this aspect of the project for you and save you considering comparable quotes that we will obtain on your behalf and appointing the selected provider. You can leave this aspect of your project entirely with us.  Building control is required for almost all projects, and for all the projects we ever worked on as only minor renovation works may be exempt.

House Extensions

FAQWhat is the cost of building an extension?
Currently we recommend allowing between £2,500 and £3,000 per square metre for side extensions, rear extensions or front extensions. For basement extensions, which are most expensive way to add space to your home, we recommend that you allow between £3,000 and £3,500 per square metre. When it comes to roof extensions, our experience shows that it is better to allow a lump sum of £40,000-£60,000 for loft conversions with dormer windows and between £80,000 and £120,000 for mansard roof extensions. These ranges are based on averages from numerous actual projects that we have completed in and around London since we established Scenario in 2007. We only use these rough costs per square metre during the early stages of design to maintain awareness of your target budget until a cost professional is appointed and more accurate methods of estimation are employed. The actual cost for your project will depend on many factors, including the complexity of the design, level of structural support required, and selection of fixtures, fittings material finishes. Using these rough ranges as a guide we will work together with you in an interactive process to optimise budget and scope and find the balance that works best for you. The estimated costs per square metre mentioned above are for the build costs only and exclude VAT and professional fees.

House Extensions

FAQWhat is the cost of an internal refurbishment?
Currently we recommend allowing between £2,500 and £3,000 per square metre for areas which will undergo an extensive renovation. We designate an area of the project as extensive renovation if the planned works includes substantial changes to layouts, significant structural works, re-plumbing, re-wiring and full redecoration. For areas of lighter internal renovation which do not require significant changes to layout or substantial structural works but do require full redecoration, re-plumbing and rewiring, we recommend allowing between £2,000 and £2,500 as an estimated cost per square metre, we designate these areas as requiring medium renovation. If there areas in your project which only call for a light renovation such as re-plastering, and painting, installing new floor finishes and light modifications of electrics and plumbing fittings, we will designate these as areas of light renovation and recommend that you allow £1,500-£2,000 per square metre or even as low as between £1,000-£1,500 if you only have light touches in mind. The real cost for your project will depend on several different variables including the complexity of the design, extent of structural works and level of fixtures, fittings and material finishes. These estimated costs per square metre are for the build cost excluding VAT and professional fees.

House Extensions

FAQWhat is the cost of building a new house?
If you are thinking about building a new house from scratch for which the term Self Build is often used, we currently recommend allowing between £2,500 and £3,500 per square metre for projects in and around London. This may sound like a very wide range initially, perhaps too wide to be useful? As soon as we can establish even a few of the basics of your requirements and aspirations for the project we can safely narrow it down and customise it to match your intentions. The key parameters that will help us to refine initial estimates are whether or not a basement is required to achieve your target floor area, the likely construction method and corresponding structural approach and of course your desired level of fixtures, fittings and material finishes. Another key parameter that we must consider right from the outset is the level of sustainability that we are aiming at, are you satisfied with the base line requirements as defined by current building regulations, or should we aim higher? Working together with sustainability experts we have created our own bespoke set of sustainability packages which allows you to place your sustainability target anywhere you wish. This can range from basic compliance to an extremely sustainable and energy efficient standard which comes with great savings on running costs, future proofing and wellbeing benefits such as improved air quality, thermal comfort, and considerate and healthier surface finishes.