Despite some pretty unpredictable weather here in the UK, we seem ever-optimistic about the climate, determined to do everything we can to ‘bring the outside in’ — and what better way to take advantage of any rare glimpses of sunny weather than with doors that allow you to open up an entire section of your home to the outdoors.

Bi fold doors with timber interior frames

Composite doors, with a timber interior finish and aluminium exterior frames are a popular option at present. These are from Wickes

What Options are Available?

You have decided you want some opening glazing within your house design, but what is the best way to go about this and how will your new doors open?

The choice comes down to:

  • French doors
  • sliding (or patio) doors
  • bi-fold (or folding) doors

French Doors

Timber French doors are the ideal addition to traditional style properties. Evolution Windows

Comparing the advantages of the different door types can be massively helpful when making your choice. French doors are:

  • Perfect addition to period homes
  • Usually provided by window suppliers so can easily be designed as part of a new window scheme
  • Easily scaled up or down — simple to combine with matching sidelights
  • Available in variety of materials and colours
  • Can be cheaper than sliding or bi-fold options

Sliding Doors

  • Frames can be so slimline that they are almost invisible
  • Can be designed as ‘pocket doors’ that slide away into cavities within the wall
  • Good for large apertures as each panel can be far wider than the typical maximum width of 1.1m for a folding sliding door panel
  • Minimal sightlines to make the most of views
Slimline sliding doors

Sliding doors, such as these from IQ Glass, offer minimal sightlines

Sliding doors run in a track within the floor and are divided into two or more panels, with one side fixed and the other ‘leaves’ sliding open in front of it.

Not every situation permits you to fold doors into the stack that comes with bi-folds and so sometimes sliding doors are more practical. And on wider openings, the option is there to split a patio door into three parts (two sliding, one fixed), creating almost as much open space as a bi-fold.

Pocket patio doorsets, where all the glazed panels slide into the adjacent wall, are ideal if the situation and budget allow.

In general, sliding doors are a little cheaper than bi-folds because the opening mechanism is simpler.

Bi-Fold Doors

  • Give a clean, sleek finish and usually run on tracks that lie flush with the floor
  • If your opening is relatively small (around 4m or less), bi-fold doors will not block much of the opening when open
  • Allow whole walls to be opened up completely — but do bear in mind ‘stacking’ space

The bi-fold or folding sliding doors, which have proved such a hit in recent years, are a marriage between opening French doors and sliding patio doors.

They come in many designs and have countless configuration options, but the common theme is that they slide on a track while still being hinged together and, when fully open, they concertina into the smallest practicable space so that the break between the house and the garden is minimised.

Folding sliding doors with insect screen

Bi-fold doors open up huge areas of wall to the outside. These integrated doors from Centor come complete with an insect screen

On a more technical note, there are many ways of designing bi-folds. They can be hung so that they open either inwards or outwards, and the configuration can be arranged so that all doors fold to one side or are split, which can be useful if you want a single ‘traffic door’ for daily use.

The tracks they run in can be configured in a number of ways too, though most people seek to have a flush floor track so that the internal and external floor levels are the same, to create that unbroken feel.

As the bi-fold market has grown, the range of choices has mushroomed too, so that they are available in a number of different materials, each with its own price implications. The current fashion is to go for frameless glass doors, which further enhance the light-gathering potential.


When it comes to making a purchase decision, you’ll need to consider the features you want and how much you are willing to pay.

While bi-folds and patio doors are now available from outlets such as Screwfix and Wickes, most self builders work with one of the many specialists in this field who usually provide an installation service.

Prices vary from as little as under £1,000 per leaf up to double that for features like triple glazing and low G factor glass.

What Material Should You Choose?

Grey aluminium bi fold doors

Coloured aluminium frames are a popular choice for both bi-fold doors as well as sliding. Kloeber

  • Aluminium is the perfect choice for contemporary homes, allowing for very slim frames on doors and comes in a range of finishes
  • If you are considering French doors because you feel they will fit in with your traditional-style home, timber will be the best option. Softwood will be the cheaper option, but will require a little more upkeep to remain in good condition than those with hardwood frames
  • Doors with aluminium exteriors and timber interiors – sometimes referred to as ‘composite‘ – offer the benefits of the beauty of the timber inside, whilst the aluminium exterior has greater resistance against the elements

Glazing Options

Self build with stained timber cladding and sliding doors

Large amounts of glazing mean it is even more important to achieve good U-values

The switch to fully glazed doors has been driven by improvements in glazing technology. Glass has always been highly valued but traditionally its use was limited because it was relatively expensive and it was difficult to regulate: too cold in winter, too hot in summer and prone to condensation. Not to mention the fact that it could shatter.

Step-by-step, these perceived problems have been addressed by glazing technologists. While glass itself will never be a good insulator, air or gas trapped between panes of glass works rather well in this respect. The efficiency of double and now triple glazing has grown steadily over time and now the glazed units themselves are more energy efficient than the frames they sit in.

In fact, the U-values of the best triple-glazed units are now down below 1.0 — three times better than what would have been achieved in the 1970s when double glazing first appeared.

In addition to this, you can now specify solar-controlled glass (look out for the G factor) that can reflect away large amounts of unwanted sunshine to help overcome summer overheating.

What is the G Factor?

Also known as the Solar Factor, it is a coefficient that measures the solar energy transmittance of windows.

With the trend towards minimal sightlines, (as low as 60mm) the performance of the glazing becomes increasingly important. Any large expanse of glazing will mean potential heat loss and you will need to choose carefully.

Building Regulations

All new and replacement windows must comply with Part L of the Building Regulations, which states that any glazed doors must achieve a minimum U value of 1.6, but you can often pay for upgrades from the standard glazing offered — reducing U-values much further (on triple-glazed models especially).

Standard double glazing is commonly 24mm or 28mm thick. It often has a low E-coating which improves energy efficiency and will be toughened or laminated safety glass that complies with Building Regulations.

Thermally broken frames are also a must in order to reduce heat loss.

How do Level Thresholds Work?

Bi fold doors within open plan kitchen diner

A level threshold is a particularly popular feature of many contemporary homes. These bi-fold doors are from Solarlux

A level threshold (where the floor track that the doors run on is flush with the floor and the internal and external floor levels are the same height) is perfect for those with mobility issues and also works well with young children, allowing them to run in and out without constantly tripping up.

However, to work successfully, the space must remain watertight and so good drainage must be incorporated into the design (try ACO’s Doorway Drain). The floor in front of the threshold should slope gently away so that water cannot pool in front of the doors.

Another option is to build up the external floor level with a timber deck, that gives the appearance of a level threshold without the risk of water ingress.

Choosing the Right Supplier

“The price range is very wide, but what a lot of clients don’t seem to realise is that the differences in quality are also very wide,” says Charlie Sharman, Managing Director at Cantifix (who supply Schuco doors).

If you’re choosing aluminium, check that the frame has been designed to be thermally broken, which will combat heat loss and condensation problems. Kloeber’s range, for instance, is made up of extruded aluminium profiles insulated with a polyamide thermal break.

Track systems also vary. Ideally they should be stainless steel and the mounting on which they sit should be extruded aluminium. The robustness of the hinges is another differential between the better and not-so-good models. Some systems use a cast aluminium hinge, which will never last with regular use and are easy to break into. Hinges on the more desirable door systems are either extruded aluminium or stainless steel.

Door systems like this are a potential area of weakness from a security point of view, so you should ensure that the doors have at least a three-point (preferably five) stainless steel lock.

The gaskets between the doors are worth checking too. They should be tight enough to provide sufficient weather protection, but as the folding doors can be a trapping hazard, soft enough to prevent serious injury if anyone gets their finger stuck.

Other key tips – according to Centor – include ensuring reliable operation by asking to see evidence of cycle testing (upwards of 25,000 actions). “Like a sail, the force placed on folding doors by prevailing weather conditions gets proportionally greater the larger the area,” says a spokesperson. Ask for pressure testing data — 1,200pa constant/1,800pa gusting pressure is a good standard.

One factor that the supplier can’t control is the opening in your wall — and as anyone with experience of building sites knows, there is a degree of room for error. So make sure that your door allows for vertical and lateral adjustment — particularly useful for allowing for any movement over time.

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