Adding a single storey extension will enhance the appearance of your valuable living space and could increase its financial value.

A single storey extension is a cost-effective solution that allows you to design extra living space with a layout that fits the way your family uses your home. With glazing rooms, it can also give you the ability to create a light space that is integrally connected to the garden. So, the benefits of a single storey extension are numerous. It doesn’t just have to be a kitchen extension, why not put a swimming pool in there? 

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The design of a single storey extension, especially the choice of its style and materials, should be one of the most important decisions you make when building. It is the design that will dictate, in addition to the layout, how long it will take to build and how much it will cost. Always remember that the design of your extension can increase or decrease the financial value of your property. You should always take this into consideration when you discuss your ideas with your architect, or with a builder.

Doors and Windows

Setting up doors and windows is key when planning your home extension. You can achieve amazing results with good planning in order to increase light and space. Why not think about bi-fold glass doors to the rear or even a glazed roof light? Also, internal doors can give you privacy. Ensure that their style and frames match the style of your interior and the furniture.

Bringing the Outside In

By combining indoor and outdoor spaces, you will make both spaces feel larger and more cohesive. Think of the wide double folding doors overlooking the courtyard, the continuous floors inside, the treatment of the walls with plants, and you will create a unique space that extends from the house into the garden.

Discuss everything you would like to achieve with your architectural team. Undoubtedly some compromises will have to be made but the team at Swoon will help you to accomplish the results you desire.

Here is a list of questions you should ask yourself before starting:

  1. What is your current situation?
  2. Why do you need to extend?
  3. Do you need an extra bedroom or is a relative coming to stay?
  4. How do you want to feel as you move through your new space?
  5. How will this extension improve your quality of life?

Planning restrictions will limit the size of your extension. However, keep in mind that the larger the extension, the more cost-effective it is. Then again, reducing the garden at the expense of your extension could deter potential buyers if you resell. It’s all about balance! 

Good planning is key to getting your extension completed on time and within budget. From checking whether you need Planning Permission or using your Permitted Development Rights for your project and sourcing the best construction team – good planning will save hidden expenses in the long run and will also give you realistic expectations of what can be achieved.  

At Swoon we have a specialist architectural team, designers, structural engineers and planning experts – we also have a dedicated team of builders that we have tried and tested and we always guarantee our structural work for 3 years. 

Under Permitted Development, there are limitations for single storey extensions:

As of May 2019 Permitted Development Rights changed. You can now build a single storey rear extension of up to 8 metres if your house is detached, or 6 metres if your house is semi-detached or terraced. We advise obtaining a Lawful Development Certificate. This will show that the construction was lawful at the time of the build. Particularly useful 30 years down the line if you re-sell.

When it comes to electricity, heating and plumbing an architect can give you the best advice including how to save money long term, choosing the best materials, and how to utilise your space to it’s best potential. They will also be able to discuss the many different options that are available when it comes to design and materials, suggest more economic options and come up with products and solutions that you didn’t know were available – it really is money well spent.

Most likely, your single storey extension will fall under Permitted Development and you won’t need Planning Permission.

Permitted Development (PD) is a type of general planning permission granted by Parliament that allows you to extend up to a given percentage in the volume of an existing house and carry out certain improvements without the need for Planning Permission.

The criteria for work carried out under Permitted Development is strict. It is advisable to check with your local authority planning office or have a qualified surveyor confirm that planning permission is not required.

Bear in mind that the Permitted Development which applies to many common projects for houses do not apply to flats, maisonettes or other buildings.  If you’ve had building work done in the past, you may have used up some or all of your Permitted Development quota.

Like Planning Permission, Permitted Development is regulated through your local planning authority. You should always speak to a qualified architect or designer to make sure your plans are compliant before you start building. Also, consider applying for a Lawful Development Certificate.

You can use Permitted Development as often as you like. Although, your allowances for extension work can only be used once. If you are buying a property, it is your responsibility to find out what Permitted Development has already taken place, modified or withdrawn.

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Application process for Planning Permission

  • An application form.
  • Evidence verifying the information within the application.
  • This would include architectural plans and elevations.
  • A site location plan.
  • A fee.

Types of Permitted Development Rights


Extend your property by 8m to the rear with a single-storey extension or 6m with a double extension, double the size that was previously allowed. Height and rear boundary restrictions apply.

The extension must not cover more than half of the garden or go forward of the building line of the original building.

It must be built in the same or similar material to the existing property.

Side extensions are permitted but subject to height and width restrictions.

Conservatories fall under the same rules.

Loft Conversion

The loft can be converted into living accommodation.

The roof can be extended by up to 40m-cubed for terraces or 50m-cubed for semi-detached and detached properties.

Dormers and roof windows can be added but must not extend beyond the plane of the roof slope at the front of the house.

Side-facing windows must be obscure-glazed.

Sheds and Porches

The external footprint must occupy no more than 3m-squared and be no higher than 3m above ground level.

No part of the porch should fall within 2 meters of the boundary of the original property and the highway.

You can build a shed or greenhouse.

No more than half the area of land around the original property can be covered.

Outbuildings must be single-storey with maximum height restrictions.

Verandas, balconies or raised platforms are not permitted under PD.

Windows and doors

The insertion of new windows, doors, skylights or roof lights is permitted (although building control may need to be notified).

A new bay window is treated as an extension.

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Do I Have Permitted Development Rights?

Most likely you do. However, remember, the slate is not wiped clean when you buy a home — any space added by previous owners since 1948 counts towards your Permitted Development allocation.

If your house is located in a Designated Area, such as a National Park, Area of Outstanding Natural Beauty or Conservation Area then your Permitted Development may be restricted or removed under what is known as an Article 4 direction. This is where rights have been removed in the interest of maintaining the character of the local area. This could also be the case if your property is listed.

single storey extension swoon architecture

Building Regulations help ensure that new buildings are going to be safe and healthy.

You have to make sure your plans comply with Building Regulations.

Building approval is a very detailed document, you can read more about it on the official Government website.

In short, you must satisfy structural integrity, fire safety, contamination and damp, toxicity, sound, ventilation, hygiene, drainage, fuel, on-site safety, conservation of fuel and power, access, glazing and electrics.

When you need approvals

You will require Building Regulation approval if you intend to carry out any new structural alterations to your home.

How to apply for Building Regulations

  1. First of all choose which type of building control body you’ll use.

    There are two types:

    1. Local authority building control body – you can apply from your council
    2. Private building control body – you can apply through a private approved inspector and they will tell your local authority about the work.

What type of application:

Full plans

Full plans are the most thorough option. You will have to submit specifications, drawings, calculations and other documents. By submitting this type of application you will avoid costly delays and reduce the risk of contravening the regulations. Decision is expected within 5 to 8 weeks.

Building notice

A Building Notice is used for smaller projects. The application is accepted when the building regulations have been met on site.  You can start work 2 days after your notice has been submitted to your building control body. However, you won’t get formal approval as you do with full plans.


Regularisation is a retrospective approval of work already carried out without consent. For this you will have to contact your local authority building control.

If you think your project should not have to comply with some part of building regulation you can always ask your local authority to ignore or relax one or more building regulations.

What happens if you do work without approval?

The local authority has to see that building work complies with Building Regulations. Otherwise, you may be asked to alter it or remove it and you will of course pay for any alterations that your council deem necessary.

building plan, floor plan, architectural

There are many reasons why your neighbours might oppose your home extensions. However, not all reasons are relevant to your local authority.

What is a Neighbour Consultation Scheme?

The Neighbour Consultation Scheme gives your neighbours a 21 day period to object, with valid reasoning, as to why your extension shouldn’t be built.

Party wall agreement

A Party Wall Agreement is a procedure for resolving disputes between neighbouring properties, arising as a result of one owners’ intention to build an extension (or other works)

Need to find out more about Party Wall Agreements?  Please download our guide.

Having an architect by your side is a wise investment. They will do all the documentation for you, choose the best builder for your project to coincide with your build and budget.

On site, they will be the person who controls everything.  A good architect will help to remove the stress and iron out any difficulties right from the planning stage to the end of the build.

Having thorough architectural drawings will make it easier for you to get the most accurate and economical build. Your architect will help you with every stage of the build giving you all options currently available and provide the best design solutions to fit your budget.

As with any building work, and before you start planning your extension design, you need to set your budget.

Building work costs around £1500 to £1900 / m² (a 4m x 5m extension would reach around £30,000). For the best quality, expect to pay between £1900 and £2200 / m². You will pay between £2200 and £2400 / m² for a high-spec extension.

When calculating costs, you will need to consider the professional project fee costs:

Architect’s fees are around 3-7% of construction costs, with planning drawings around £2700 and construction drawings also around the £2700 mark.

For roof rails and foundations, you will need a structural engineer. This will cost approximately £500 to £1000.

The survey will cost between £500 and £1500 if research on an existing home is required.

Project Management: 3-7% of the construction cost for project management (you can arrange a daily or hourly rate). You can save money here if you can manage the project yourself.

VAT: 20% of labour, materials and services.

Planning Fees: For a single storey residential allowance in England, the application fee is £206. If you need a certificate of legal development, you will pay £103 and cost £34 per the requirement to meet planning requirements.

Building Control Fees. Depending on the size of your extension, plan for between £200 (for an extension of 10m²) to £ 900 (for 80 to 100m²).

Party Wall Agreement. This typically costs from £700 to £1000 per neighbour.

Extra fees: these can include a tree report (from £250 upwards), flood risk assessment in floodplains (from £250 upwards), an ecology report, as needed from your local authority (from £400). An archaeological report, obviously only needed if your home is in an archaeological location and a historical construction report, probably if your home is listed. Just when you thought this couldn’t get any worse….don’t forget interior design!!

The cost to furnish the interior of a single storey extension largely depends on the type of room you are adding, but expect to pay approximately:

Between £5000 and £30,000 for a new kitchen, depending on specification (larger kitchens can cost significantly more).

The bathroom will cost from around £4500 to £11000. Depending on the quality of the equipment. A shower will cost a similar amount.

For floors, the budget is £25 to £100 per square foot.

For wall and ceiling linings not covered by construction costs, set aside about £240 per square metre for plaster or dry lining, plus paint.

Expect to spend between £1500 and £2000 per linear meter for double or sliding doors. These are a great way to bring in light and connect your home to the garden. It will also create the feeling of more space.

Remember to include the cost of adding heating to your new room. Costs for underfloor heating vary. Electric underfloor heating is less expensive to install. However, it’s more expensive to use than water supply (and some elements can be installed on a do-it-yourself basis). Although, underfloor heating is more expensive to install and may require the addition of a new boiler to meet demand, it is less expensive to operate in the long run. Expect to pay around £2500 for a new boiler. Expanding an existing single storey central heating system can mean no more than two to three days for the plumber, about £150 a day without materials.

For utility rooms, calculate £1500 to £11000, according to the room size and level of shackles.

Therefore, this all adds up to approximately £45,000 for a 4m x 5m single storey extension of basic quality. This includes most fees but excludes the interior design costs.

But DO NOT PANIC!!!  Talk to an architect about your design, get involved and see where compromises can be made and go from there. Don’t start knocking walls down until you’ve sought good quality, sound advice!  Talk to Swoon and good luck!



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