Extensions with bi-fold doors—how to build them

Author Profile
Ben Brocklesby is the Sales and Marketing Director at Origin. On top of this, Ben has always had a vested interest as his wife, Victoria, was one of the original founders of the company in 2002 and is now COO.
Ben has been building his house from scratch for the last 18 moths, so has built up a wealth of knowledge in building works, knowing what works and what is likely to add value to a home when it comes to resell. Needless to say, Ben has specified one or two sets of Origin Bi-fold Doors and Windows throughout the house.

By Ben Brocklesby

The right set of bi-fold doors can be the ideal finishing touch to any modern home extension. But first you have to build it!

In this guide, we talk about the main things to consider when building an extension, including what you can expect to pay and who’ll you need to hire to do the work. We give you some ideas for incorporating bi-fold doors and direct you to the best set of doors for your particular project.

Looking for bi-folds for a different part of the house? Read our other location guides:

Click a link to jump to the relevant section:

Where to start—deciding what size of extension is best
Costs and budgeting
Who to use—architects, surveyors, builders and engineers
Planning permission and laws
Design ideas for extensions with bi-fold doors
Selecting the right bi-fold doors for your extension

Where to start—deciding what size of extension is best

When extending your home, you should aim to build the largest possible extension for your highest possible budget.

Your intention should always be to get as much value as you possibly can from the project. We don’t just mean increasing what your property is worth (although that’s one big benefit!). We also mean the value that comes with the additional space you’re creating and the lifestyle changes it will bring.

Size considerations

Your first step is to figure out how much space you have to work with, and what size of extension will suit that space best.

This means considering the following:

Size of your garden—a large rear extension in a small or medium-sized garden may actually lessen the value of your home if it makes the space look unbalanced.
Space inside the home—adding an extension is the perfect opportunity to expand your home’s existing layout. Consider removing internal walls to open up the space further, rather than simply extending the size of a single room.
Purpose of the extension—what will you use it for? If you’re not planning to move home in the near future, you can design a space to suit your tastes and needs exactly, rather than one aimed at appealing to potential buyers. Think about what extra space you require and how you’ll make use of it.

Knowing this also helps you understand:

what the project will cost
what materials you need
whether you’ll have to apply for planning permission

How bi-fold doors factor in

If you’re planning to install bi-fold doors as part of your new extension, the size of the extension will dictate the number of door leaves you can include in your design.

With bi-folds, generally “bigger is better”. However, this could mean that you would need to spend more on supporting steels, so take this into consideration when discussing your plans with an architect. Having a large amount of glazing will give you a greater feeling of space and light inside your home.

Costs and budgeting

Basic building costs

It costs around £1,000–£2,500 per square metre (m²) to build a rear extension.

The table below shows how that cost breaks down according to the type of extension and the quality of the specification.

Quality of build/finish (See below)	Type of extension
	Single-storey extension	Two-storey extension
Standard quality	£1,000 to £1,680/m²	£1,320 to £1,620/m²
Good quality	£1,680 to £1,920/m²	£1,700 to £2,000/m²
Excellent quality	£1,920 to £2,160/m²	£1,800 to £2,500/m² or more
	Note: These figures include materials and labour only. See ‘Additional costs’ below.

*Source: https://www.homebuilding.co.uk

A two-storey extension is similar in price to a single-storey extension because the only difference to the structure—after the roof and foundations—is the additional walls and floor joists. These only slightly increase the overall cost per square metre.

Additional costs

The figures in the table above include materials and labour only. There are extra costs that you’ll need to budget for, including the following:

Type of cost		What you’ll pay
Planning application fees		£206 (as of June 2019)
Building regulations fees		£500–£1,000 (depending on size of project)
VAT		20% on: materials labour (unless you use a tradesperson who isn’t VAT-registered)
Fees for professionals (See ‘Who to use’ below)	Architect	7%–15% of the total building costs
	Structural engineer	£400–£4,000 (depending on size of project)
	Surveyor	£500–£1,500
	Project manager	3%–7% of the total building costs
Party wall agreement (See below)		£700–£900 (per neighbour)

*Source: https://www.homebuilding.co.uk

And remember to factor in costs for fittings, fixtures and finishing touches such as:

steelwork
flooring
central heating
lighting/electrics
wood/gas stoves

Factors that affect the cost of an extension

Location

Where you are in the UK matters. Extensions are generally more expensive to build in London and the South East. A 5m x 5m extension that costs £30,000 in northern England might set you back more than £50,000 in the capital. And that’s for the building work alone.

Quality of build/finish

Like with any building project, the quality of the extension obviously depends on the standard of the builder or developer.

The cost of the foundations and main structure shouldn’t vary too much between different-quality builders. It’s with features such as roofing, wall cladding, flooring, and fixtures and fittings that you’ll notice an increase in quality the more the price goes up.

Build route

This means the degree to which you get involved in the building project. For example, do you:

build most of the extension yourself and enlist help only for the more specialised work?
hire a contractor to do everything?
employ a main contractor, who hires subcontractors to do part of the work?

The more DIY work you do, the lower your costs, as you’re not paying as much for labour and you’re buying the materials directly from the suppliers. It’s when you hire a contractor to do all the work that you’ll pay a premium for labour as well as materials.

Before you dig

It’s important to check utility maps online before you start digging. LinesearchbeforeUdig is a free service designed to keep you safe by reducing the risk of death and injuries caused by striking assets such as pipelines and cables. It will also help you avoid any unexpected costly damages.

Type of ground you’re building on

There are many different types of soil—for example, clay, chalk, rock and so on. Knowing which one you’re building on is crucial if your extension is to have the correct foundations.

If the work to install foundations is particularly complex, the cost will increase.

Funding your extension

It’s likely you’ll need to take out a loan to pay for your extension. If this is the case, speak to your mortgage provider about adding the cost of the extension to your mortgage. Alternatively, you can take out a separate personal loan.

One big advantage of a personal loan is that you can clear the cost much more quickly than if you add it to your mortgage, although interest rates are likely to be higher.

Planning for contingencies

It’s wise to include a contingency fund on top of your budget to cover any unexpected extra costs.

Work out exactly what your contingencies might be and earmark funds that will allow you to absorb the additional expense. Generally, a contingency budget of 10% of your total costs is recommended.

It’s much better to plan for any extras in advance rather than having to rely on credit cards or last‑minute loans if costs begin to soar.

Who to use—architects, surveyors, builders and engineers

Architects

Architects design your extension and are trained to see the bigger picture. So while your builder pores over materials, your electrician fixates on light fittings and you consider styles for your new kitchen, an architect brings all these elements together.

They will listen to what you want from your build and advise you on the best way to achieve it, making sure that every inch of space and light is put to use. They will tailor their design to your exact specifications and make you aware of any potential obstacles or issues.

Architects help with the planning process and have the experience to navigate it so you have the best possible chance of your plans being approved. Choose one who’s familiar with your local planning authority and knows what might or might not gain approval.

A further bonus of using an architect is that they will often have a crew of trusted experts (including plasterers, builders and electricians) who they use regularly and can rely upon. This will save you having to find and hire professionals yourself. However, it’s still worth getting quotes from other professionals to confirm that your architect’s recommended experts are competitively priced.

How to find an architect

Visit the website of the Royal Institute of British Architects, a professional body for architects in the UK and across the world. There, you can search for qualified architects and find advice on what architects do and how to use one.

Surveyors

A surveyor’s job is to make you aware of any problems you might encounter with your extension, before you begin work. They will carry out a full survey and advise you on:

potential damage to timbers
potential damp issues
whether you need to install more damp-proofing
faults with the building’s structure

They can also offer advice on the planning permission and building regulations approval you’ll need, and can draw up building plans and a budget for proposed changes. Surveyors can project-manage your build from start to finish.

Architects can also do much of the above, so it’s worth speaking to yours before you go to the additional expense of hiring a surveyor.

How to find a surveyor

If you decide to hire a surveyor, you can find reputable ones via the Royal Institution of Chartered Surveyors.

Builders

Your builders actually construct your extension, in line with your architect’s plans and designs. They are the people you’ll have the most contact with, and who you will be responsible for managing. Alternatively, you might choose to hire a project manager, or your architect may fulfil this role.

To read more, see the ‘Build route’ section above.

Other building professionals you may want to hire include:

electricians
bi-fold door installers
plasterers
tilers
floorers
interior designers
Gas Safe engineers

How to find a builder

Going online to find a builder can be daunting. A useful place to start your search is at the website of the Federation of Master Builders (FMB).

The site has a search tool that enables you to find tradespeople and see their references. All FMB members are vetted, inspected and checked to make sure they have the proper insurance.

To find builders local to your area, use Checkatrade.com or the Guild of Master Craftsmen.

For tips on hiring a builder, see the Telegraph’s guide on How to find the best builder for your home.

Structural engineers

A structural engineer makes sure any changes to the building won’t compromise its structure.

They provide advice on what materials to use and work closely with the architect, giving guidance on aspects such as steel beams, floor joists and load-bearing walls.

Planning permission and building regulations approval

Planning permission

For your extension

No matter what size of extension you’re looking to build, always check whether you need planning permission. Not all extensions require it, but it’s very important if your home is:

situated inside:
- a national park
- a conservation area
- an area of outstanding natural beauty
a listed building

Providing your extension meets certain criteria, it will be classed as a permitted development. These criteria include:

not being more than four metres in height
not including a balcony or veranda
not extending above the highest part of the existing roof
using materials that match the outside of the property

You can find the full criteria on the Government’s Planning Portal website.

Even though it costs only £206 to apply for planning permission (as of July 2019), it can often take months for permission to be granted. With this in mind, it’s certainly worth considering whether your plans can fit the conditions for permitted developments.

Neighbouring properties

You must also consider how your extension will affect your neighbours.

A single-storey extension is unlikely to have an impact on your neighbours’ homes (except for the disruption the building work causes). However, a second-storey extension could obstruct their view, block sunlight to their garden or—in an extreme case—encroach on their property and affect the value of their home.

Under the Neighbour Consultation Scheme, the Government allows homeowners to build large extensions without getting planning permission, providing that their neighbours don’t object.

Also keep in mind that if you’re building an extension near the boundary of your neighbours’ homes:

it must comply with the Party Wall Act, a law that determines how shared walls are treated
you must give your neighbours at least two months’ notice before you start work

Your neighbours might ask for a party wall agreement—a legal settlement that sets out exactly what kind of work you’re allowed to do. This can cost up to £700–£900 per neighbour.

This is why it’s useful to tell them your plans from the very beginning—you might be able to cut costs by sharing a surveyor, for example.

For bi-fold doors

If you decide to have bi-fold doors installed as part of your new extension, you shouldn’t need special planning permission. The criteria that apply for bi-folds apply for extensions as a whole—for example, if your home sits inside a national park or is a listed building.

If you’re granted planning permission for the extension itself, you won’t need separate permission to fit bi-fold doors.

Building regulations approval

Most extensions require approval under the Building Regulations.

Building regulations are different to planning permission in that they focus on the design and construction of the building. They ensure that any changes made won’t have a detrimental impact on you and the people in your household. They also include energy efficiency considerations.

Read more about building regulations approval on the Government’s Planning Portal website.

Design ideas for extensions with bi-fold doors

Incorporating bi-fold doors into your rear extension enables you to enjoy the many benefits of open-plan living and alfresco dining.

Here are some design ideas that we hope will inspire you to build a practical and great-looking extension that meets your needs and budget.

Small extensions with bi-fold doors

One major feature of bi-fold doors is that they let in lots of natural light. Bringing daylight into your extension will enhance the space and give it a sense of calmness.

Combined with a tall ceiling and/or skylight, bi-fold doors can completely transform a small room, making feel more spacious and impressive.

Kitchen extension with bi-fold doors

Many homeowners use bi-fold doors to separate a kitchen from a dining area, or to use kitchen bi-fold doors that open out onto a patio, garden or outdoor living space.

In the above image, an Origin customer has completely replaced one kitchen extension wall with an 8-door set of bi-fold doors and an adjacent wall with a 3-door set. Not only does this make a striking impression aesthetically, but it provides functionality in terms of allowing the homeowners to entertain guests in the large garden and patio area.

Read the full case study

Find out more about kitchen bi-fold doors

Flat-roof extensions with bi-fold doors

Flat-roof extensions are probably the most common form of home extension in the UK. They are usually cheaper to build than pitched roof extensions and allow for a much wider range of design possibilities.

Combined with rooflights or roof lanterns, they can create a room which is well lit, bright and airy.

Although they are sometimes accused of being vulnerable to leaks due to pooling rainwater, this isn’t entirely true or accurate. The materials used to construct the roofs are designed to be fully waterproof and withstand any kind of bad weather.

Open-plan extension with bi-folds

When adding an extension, it makes sense to rework the existing layout. Reconfiguring a room enables you to achieve the best possible layout in terms of access, views, natural light and privacy.

Removing internal walls and doorways to create a larger open-plan space can be of real value in improving the flow between rooms.

Selecting the right bi-fold doors for your extension

When choosing bi-fold doors for your rear extension, you have a number of decisions to make.

1. Do you want bi-fold doors, sliding doors, French doors or something else?

Bi-fold doors are a popular addition to home extensions as they create a huge sense of space. Even when the doors are closed, the floor-to-ceiling glass makes the interior and exterior feel like one large, open area.

Extremely versatile, the doors fit any size of opening—even corner or bay spaces—and can open outwards or inwards.

Sliding doors work particularly well when there’s a large aperture to fill, as their narrow sightlines give you the widest possible view of your garden. French doors work very well too.

2. If bi-folds, do you want them to be made of aluminium, uPVC or timber?

Once you’ve settled on bi-folds, you need to decide what kind you want. Bi-fold doors generally come in aluminium, uPVC or timber, although naturally we recommend aluminium bi-fold doors, for a number of reasons:

They last longer
They’re very strong
They need very little maintenance
They won’t warp
They allow for slimmer frames, giving you better sight lines, wider glazed panels and a more expansive view

3. How many door leaves do you need?

Bi-fold doors come in a wide range of configurations, allowing you to customise your new doors to match the style and design of your extension exactly.

4. What colour, locking systems and handles do you want them to have?

No bi-fold doors are complete without a bespoke finish, locks, handles and hardware. You’ll have a huge variety of colour options and be able to choose from a wide range of handles and locks.