Single Storey Extension

Single Storey Extension

Single Storey Extension

Single Storey Extension About us

Finding your dream home is a huge achievement. But a dream home rarely remains that forever. Over time, our lifestyles change and our homes must adapt. A 21st-century home must be all things to its owners: a place to work, to entertain, to raise a growing family and to grow older. If you don’t want to move, your home must improve.

A single-storey extension is a way around these changes in your life. Adding more space to the side or rear of your home – or both – is a necessary luxury that will work hard to play different roles as your needs evolve. A skilled architect with knowledge of your way of life, your future plans and your neighbourhood will help develop your space to accommodate your present and your future.

Single Storey Extension Your Single Storey Extension project

We launched Scenario in 2007 with a vision to adapt heritage architecture to 21st-century living. A highly functional home is the product of a deep understanding of the ways in which homeowners engage with their space. We work in close collaboration with our clients to make sure their needs sit at the forefront of every tailor-made design.

Our landmark project Scenario House demonstrates our commitment to the modern needs of homeowners today. The home was shortlisted for a RIBA London Award in 2018.


To discover whether or not your architect has had success steering planning applications through your local council, visit the “planning applications” page of your local council’s website and enter the architect’s name in the search criteria.

Single Storey Extension

Single Storey Extension

Scenario is an established architecture practice focusing on contemporary residential design. We take on projects of every scale and scope, from home refurbishment, renovation and expansions to new-builds.

Single Storey Extension Working with Scenario Architecture

At Scenario, we tackle domestic projects of every scale and complexity, from single-storey extensions to full renovations and new-build homes. Our dynamic London studio offers a bespoke architecture service.

Our highly skilled architects collaborate closely with every client from the initial drawings, detail design and planning through tender and construction to completion – on time and on budget. If you are planning a single-storey extension, check out our portfolio of residential projects across London.

Real-time 3D design technology is the most efficient tool for seeing through a project, choosing fixtures and fittings and simulating natural light. We use innovative technology and virtual reality on all our projects. This Chartered Institute of Building case study, featuring a Scenario project, demonstrates the benefits of this advanced technology for domestic architecture.

Scenario is a RIBA Chartered Practice. We comply with the strict health and safety criteria of the country’s professional body.

Single Storey Extension

Single Storey Extension In our client's words

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Single Storey Extension Further Reading

“Don’t move, improve,” goes the saying. And it works for most. If you love your location and find moving house a daunting proposition, there are measures you can take to expand and transform your existing home, and a single-storey extension is one of the least intrusive and least expensive options. These common home-extensions require fewer official hoops to jump through, less substantial foundations and minimal steelwork. And if they’re built well, they may also be able to accommodate a second-storey in the future.

At Scenario we design home extensions of every size and scope, within the planning constraints of the neighbourhood. We always recommend adding the most space to the home as permitted, without dramatically reducing the outdoor space. Generally speaking, the larger the extension, the more cost-effective it should be.

In a terraced house, a single-storey side-return extension is a popular way to gain valuable square footage and open up a warren-like layout. The addition of just a few square metres can allow for an open-plan kitchen-diner with a family room and separate bathroom and utility room that flows into the original lounge and hallway. A semi-detached house would benefit from a wraparound addition that occupies the side-return and reaches around into the rear garden. This would completely transform an old property into a functional home for generations.

Aside from space, one great advantage of a single-storey extension is the gaining of natural light. Single-storey additions can be glazed in any number of ways, from rooflights to Velux windows to bi-fold and concertina doors. Moreover, the redesigned layout will enable you to enlarge doorways and existing windows and push up your roof to allow in even more daylight. Enlarging windows and doorways also increases the sightlines throughout a home, making it feel bigger and safer.

If you have a garden, extending to the rear or side of your home creates an opportunity to connect indoors and out with walls of glazing and new flooring that can be carried through outside.

We also like to make sure a home-extension will allow the house to grow with the homeowners. As families progress and age, we expect generations to come and go, rooms to change function, bathrooms to work harder and people to require more assistance as they get older. This is where wider doorways, smooth transitions and large, highly functional kitchens and bathrooms to come in handy. After all, if you don’t want to move house now, you really won’t want to move house later.

Single Storey Extension Frequently Asked Questions

    There is no doubt that choosing an architect is a big decision and there’s a huge amount of information to consider. As you may have already experienced, different firms and architectural practices across London tend to differ in terms of the language they use, which aspects they emphasise and in their fees and scope structures. We have compiled an essential guide to choosing an architect, which includes the three most important considerations to have on your list whilst you come to a decision. This guide is based on our fifteen years of experience as a top architectural practice in London and includes our expert recommendations to ensure you make the right choice and select the architect that is best suited to you and your project. Click here to read the full guide.

    Single Storey Extension

    FAQHow should I decide which architect to work with?
    The scenario design process was developed, tested and perfected through over a decade of extensive delivery of residential projects within and around London, some of its key features are listed below:   
    • Scenario based design – We start each and every project with a meticulous analysis of our client’s vision, requirements and aspirations. We do this by asking our clients to imagine their everyday scenarios living in the completed house and describe their desired interaction with it. 
    We then translate the resulting high definition brief into an informative and revealing 3-dimensional simulation, illuminating aspirations, requirements and patterns of habitation. 
    • Uniquely interactive - Our client’s deep involvement in the process does not stop with completion of the brief. Our design meetings are highly interactive, informal and fun. 
    Sitting together in front of a real time 3D model of the proposed design with realistic materials, lighting and textures we push and pull the proposed scheme together to explore its full potential and drag and drop different materials to explore various options. hen we invite our clients to take a virtual reality tour through advanced equipment that is always available in our practice for our clients to explore their projects at different stages of development. 
    • Designed to reflect you – Based purely on your lifestyle, aspirations and requirements and free from externally imposed concepts, metaphors and pre-conceptions, a completely fresh and unique design will gradually emerge and it will tell your story not ours. 
    It will not look like an image cut out of a trendy architecture magazine and not designed to intentionally impress anyone. It will feel familiar, warm and inviting and you will recognise yourself in it because it will be a genuine expression of the unique way in which you and your family wish to interact with it and enjoy it for many years to come.

    Single Storey Extension

    FAQWhat is unique about the Scenario design process?
    Any architectural project comprises three main aspects, Creative design, Technical design and Project Management. A successful architectural project can only be achieved when all three aspects are properly performed and harmoniously integrated by an experienced professional. But can we really except a single person to specialise and shine in all three aspects and furthermore skilfully negotiate and balance the often contradictory challenges these aspects present? The basic assumption underlying the common structure of almost all other architectural practices today is that it is possible and this is precisely what is expected from the lone and often junior Architect that would typically be assigned to run your project start to finish. Scenario works in a completely different and new way, we believe in specialism and teamwork and therefore assign three experienced specialists for each and every project. A project team in Scenario is composed of a Project Director, a Designer and a Technical Designer, seamlessly collaborating to deliver results, which are noticeably superior to anything that a single person, skilful as they may be, could ever produce.

    Single Storey Extension

    FAQWho will be assigned to work on my project?
    A key aspect, absolutely necessary to ensure successful delivery of your project is appointing a suitable and competent professional team. If we work together on your project we would be appointed as your Architects and Lead Consultants and help you to assemble the rest of the professional team. Most projects in and around London will require at least four additional consultants, a Structural Engineer, a Quantity Surveyor for cost control, an Approved Inspector to ensure and certify compliance with building regulations and a Party Wall Surveyor if any work is to be done to a party wall or structure. For some projects, depending on scale, complexity and your specific aspirations it may be recommended/required to use the services of additional consultants. Including but not limited to: Planning, Heritage, Right of Light, Landscape Designer, Audio Visual and Building Services Engineer. When appropriate, we will discuss these options with you and obtain relevant quotes for all additional consultants for you to consider.

    Single Storey Extension

    FAQWhich additional consultants are required for my project?
    Planning in the U.K in general and in Greater London in particular is admittedly a tricky business. It is a complex maze of policies, standards and regulations that requires specialised and up to date knowledge and skills to navigate successfully.  Over the years we developed a strong approach and an effective methodology, allowing us to maintain an outstanding track record stretching over more than a decade. Successfully securing planning permission for our clients across Greater London and the Home Counties.  The key aspects of our approach to planning are listed below: 
    • Collaborative – We start the conversation with planners early and advise most of our clients to seek pre-planning advice prior to submission of a full planning application. Our experience shows that when properly consulted and liaised with, most planning case officers will be receptive to conduct a professional dialogue, increasing chances of successes. 
    • Strategic – We tailor a custom planning strategy for each project based on its circumstances such as planning history, local context and specific challenging elements. We sometimes split applications or introduce minor tweaks to the scheme during the consideration period in conversation with the officers to prevent one contentious element from jeopardising approval of the main scheme.
    • Professional – Our experience shows that the quality and clarity of the submission in terms of background research, planning history of the property and context, precedent and of course the arguments presented to support the case has a tremendous effect on success rate. 

    Single Storey Extension

    FAQWhat is Scenario’s approach to planning?
    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.

    Single Storey Extension

    FAQHow long will it take to obtain planning permission 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.

    Single Storey Extension

    FAQWhat is pre-planning and will it be required for my project?
    In the past, it was common practice for local authorities to impose sustainability standards on residential developments. However, the 2015 Deregulation Act removed the obligation on local authorities to require any standard at all, which means the only requirements having fallen back to those of the Building Regulations.  With no clear and improved targets to work towards, in collaboration with Envision (, we have created optional Sustainability ‘Levels’ to offer our clients the chance to drastically improve the sustainability credentials of their home. These ‘Levels’ encompassing Bronze, Silver, Gold and Diamond, traverse a clear and applicable route from basic compliance with current Building Regulations all the way to the full and rigorous HQM (Home Quality Mark) certification within Level Diamond. As the packages become more elaborate in terms of sustainability, analysis and implemented measures, they provide increasing tangible benefits. Ranging from thermal and acoustic comfort and wellbeing, to reduced carbon foot print, savings on running costs and significant advantages through the planning process.  The more elaborate packages obviously entail higher cost in terms of professional fees as well as impact on the construction cost, although each sustainability ‘Level’ will endeavour to not overly burden the construction budget.

    Single Storey Extension

    FAQWhat is Scenario’s approach to sustainability?
    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.

    Single Storey Extension

    FAQWhat is building control and is it required for my project?
    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.

    Single Storey Extension

    FAQWhat is the cost of building an extension?
    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.

    Single Storey Extension

    FAQWhat is the cost of an internal refurbishment?
    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.

    Single Storey Extension

    FAQWhat is the cost of building a new house?
    The fee structure that we will offer will depend on the type and scale of your project as well as the scope required from us. The vast majority of the projects we take on are what we call ‘full projects’, these are projects for which we will provide full Architectural services from inception to completion, covering the standard scope of services offered by most RIBA Chartered Architects and more. For these full projects our fees will be calculated on the basis of an agreed percentage of the final cost of the building works exclusive of VAT and professional fees. At any given time, we will calculate our fees based on the latest construction cost estimates available until the final cost of the building works has been ascertained. Our fees will be adjusted both forward and retrospectively to reflect any increase in budget and scope of the project, and forward only (due to work already completed) to reflect any decrease in budget/scope. During early stages, our fees will be calculated based on our in-house estimation tool and once available, on estimates by the appointed Quantity Surveyor, followed by actual prices of returned tenders and finally, the contract sum reflecting any changes during construction. Under unusual circumstances we may agree to take on projects only up to a certain stage, for example up to planning, and sometimes from a certain stage if we are taking over from another Architect. For these ‘partial scope projects’ we will normally put forward a simple fixed lump sum proposal.

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    FAQWhat is the fee structure used by Scenario Architecture?

Single Storey Extension Single Storey Extensions: A Simple Way to Add Valuable Extra Space

It’s easy to understand why a single-story addition is a popular home renovation. It will provide crucial additional space that, when coupled with an interior redesign, can significantly enhance the layout of your house and the flow of natural light, and it can also (in many instances) be completed within the Permitted Development limits. It’s also a lot less expensive than moving house to gain more space, and will add value to your current home too. Read on for some useful information about why single storey extensions are a good idea and how to get started with yours.

How Much Does A Single Storey Extension Cost?

Before you begin planning the design of a single-story extension, you must first establish a budget and verify that you can afford what you’re planning. Begin with construction expenses, which can be broken down as follows:

  • If you’re on a tight budget, you can construct a single-story addition for about £1,500 to £1,900 per m2 for low quality (e.g., 4m × 5m expansion would cost around £30,000).
  • Expect to spend between £1,900 and £2,200 per m2 for good quality (e.g., £38,000 for a 4m x 5m extension).
  • A high-spec extension will cost between £2,200 and £2,400 per m2 (eg up to £44,000 for a 4m x 5m extension).

As well as these costs, you’ll need to think about:

  • Architect’s fees (these will be somewhere between 3 and 7 percent of the cost of construction, plus drawings)
  • Structural engineer (between £500 to £1,000)
  • Surveyor (between £500 and £1,500)
  • Project management (between 3 and 7 percent, of a fixed fee)
  • VAT (20 percent)
  • Planning fees (£206 in England)
  • Building control charges (usually between £200 and £900)
  • Party wall agreement (up to £1,000 per neighbour affected)

Depending on your project, you may not need all of these additional experts to help you. For example, you can manage your own project, and you will only need a structural engineer if roof joists of foundations have to be moved, removed, or added.

Is Planning Permission Required For A Single Storey Extension?

A single storey extension that: covers more than half of the land surrounding your home; extends towards a road; increases the overall height of the building; extends more than 6m from the rear of an attached house; extends more than 8m from the rear of a detached house; is taller than 4m; or uses more than half of the land surrounding your home (or a combination of these things) will require planning permission.

A competent architect or builder will be aware of these restrictions, but it’s best to double-check to prevent multiple planning applications and to ensure that planning isn’t neglected entirely. Remember, if the extension’s height and footprint satisfy permitted development requirements, you may be able to construct it without obtaining planning permission.

Never assume anything, though, particularly if you reside in a Conservation Area. You should apply for a certificate of lawful development from your local authorities even if you don’t need planning permission, just to be sure.

Single Storey Extensions And Building Regulations

Any kind of extension must adhere to building regulations, even if you don’t technically need planning permission for it. You must apply for the work via your local authority’s building control department. Each authority has its own set of fees, or you may prefer to use a private licenced building control company. Some contractors are building control certified, which means they can do work without contacting the building control department.

What you choose is always going to be down to you, your circumstances, and your personal choices, but the end result must be an extension that meets all necessary building regulations.

Do I Need A Party Wall Agreement?

Depending on the relationship you have with your neighbours, you may be able to convince them to sign a party wall agreement waiver form. No matter what the situation, you’ll need to show them your plans and take them through all your ideas for your single storey extension so that they fully understand what you are thinking of doing.

If they’re not close friends, or you think it would be better to go through more formal channels, you will need to employ a surveyor to establish party wall agreements. Remember, your neighbours have the right to find their own surveyor if they do not wish to share yours, and you’ll need to bear the cost of this.

How Big Can The Single Storey Extension Be?

The size of your single storey extension will be limited by planning permission restrictions, such as how much your home has previously been expanded, but keep in mind that the bigger the extension, the more cost-effective it will be. However, an extension that significantly decreases the size of the garden may have a detrimental effect on the attractiveness of your house to potential purchasers. The key thing to think about is whether or not you should go big just because you can.

Designing A Single Storey Extension

Here are some things to think about whether you’ve hired an architect or are designing your extension yourself with the help of an experienced builder. The kind of extension design you select will depend on the style of home you are working with, even though it’s sometimes mandated by planning permission or permitted development regulations too.

When planning an extension, it is easy to forget about how the remainder of the home will sit alongside the new area. In the early planning stage, consider carefully how to integrate the new single storey extension with the existing areas of the property.

Before you begin planning, think about your requirements. What are you using the extension for, and how will it work with the rest of your property? You might be extending your kitchen to create a kitchen diner, for example, in which case you’ll be looking for a more open-plan layout. Or you could be adding a home office, which means you’ll need it to be enclosed. Once you know your reasons behind the extension, you will have a much better idea of how it will need to look.