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Internal Bifold Door Sizing

Many customers are challenged when trying to choose the correct size of internal bifold doors to meet the opening that they have. How do you measure, confirm and select the best interior door size option for you?

How Do You Measure Your Bifold Door Opening?

The correct measurement for a structural opening is from the sub-floor (i.e. from floor board/concrete, or whatever base you have underneath your floor covering)  to the lintel above the opening (not a plaster line, or existing frame lining). All interior folding door systems come with their own frame, in which the head tracks and running gear are hidden. So, it's vital you measure these before deciding on the size of bifold door you need.
Once you know the structural height, width and depth of reveal of the opening, you can move to the next stage in the selection process.

How Do I Size My Internal Bifold Door Product?

Door style is obviously key to you as the customer. When it comes to internal bifolding doors, there are literally thousands of sizes and styles and opening patterns to choose from. So our suggestion is to first look at the actual door style, whether oak, prefinished oak, or white primed, with clear or frosted glass, and whether you want one pane of glass per door, or four – there are plenty to look at!

Shop our range of internal bifold doors. Stunning folding glass doors to open up your home. Free delivery on orders over £750!

Choosing the Nearest Size and Door Pattern

Almost all structural openings are different – standard heights (sub-floor to lintel) vary between 2000mm and 2100mm in height, and widths can be as small as 1400mm right up to 4000mm or more, but what's best for you really depends on the nearest size to your opening.

  1. Height: If your structural height is up to 50mm smaller than the outer frame height of one of our standard products (all outer frame sizes are given for each size option on screen), then the standard product can be trimmed down to suit (i.e. the doors and frame). Trimming the frame is as straightforward as making cuts to sections supplied. Doors must be trimmed as follows:          
    • i. Trimming on height of any of our interior bifold doors may well cause you to cut into the core material of the door (which could be chipboard, MDF, or engineered softwood sections). This is fine as long as you trim proportionately to the rail size (i.e. generally more off the bottom of the door than the top ).
    • ii. After trimming, but before installation, you must seal the cut edges of the door to prevent any airborne moisture ingress affecting the door in the long term. This can be done with varnish or paint.
  2. Width: We always give you recommended structural opening heights and widths for when you're sizing our internal bifold doors, particularly for those customers creating a opening for our products. However, many customers are using our products in a refurb situation where there is an existing a hole in the wall. In this instance trimming of doors may be required. All of our internal bifold door leaves have a minimum 10mm solid timber edging (lipping) down each side of each door panel. This allows you to trim up to 6mm off each side of each leaf.
    So for instance, when sizing a 3-door set you can trim the set by 12mm per leaf, or 36mm in total off the width. On a 4-door set this increases to 48mm, and 60mm on a 5-door set. Professional joiners may also be able to take up to 10mm off the outside of each frame jamb giving you scope of around 50-56mm available reduction on a 3-door set width, 68-70mm on a 4-door set width, and 82-84mm on a 6-door set.

Don't worry though, if you've over-measured, we have a guide to help: Making Adjustments To Internal Bifold Doors.

Explaining Door Opening Patterns

When choosing and sizing your interior bifolding doors, you have to take into account that even numbers of doors folding to one side will mean that you lose the ability to open one door in isolation as a daily access door. (i.e. doors are in a screen, but you want to use just one to get through). This is because there is a connection into the head track every second door. Almost all of our standard off the shelf systems are supplied with a daily access door option.

2 + 0 – This set has 2 doors folding to one side (no daily access door)

3 + 0 – this set has 3 doors all folding to one side, with a daily access door attached to the folding door stack.

2 + 1 – This set has 2 doors bifolding to one side, and the daily access door operating off the other side frame jamb.

2 + 2 – this set has two doors bifolding to each side. (no daily access door)

3 + 1 – this set has 3 doors folding to one side, and the daily access door operating off the other frame jamb.

4 + 1 – this set has 4 doors folding to one side, and the daily access door operating off the other frame jamb.

Sizing Your Internal Bifold Door - Frequently Asked Questions

I have found a product that I think will work, but it’s a bit smaller than my structural opening by a few centimetres, can you offer me a solution?

ANSWER – Your joiner can pack out the standard frame by up to 50mm each side, using standard softwood sections. Once the installation is complete you can cover these timbers using standard architrave sets to finish the job, with a matching finish.

Whats the difference between outer frame size and structural opening size?

ANSWER - The difference between the structural size (i.e. the size of the hole you have), and the outer frame size is typically 10mm of width, and 6mm of height. This allows your installer some space to be able to fit the frame in the hole, packing it as required, so the finished frame is absolutely square, meaning your system will fit properly.

My floor is uneven, will it affect the door operation?

ANSWER – Yes. If the frame isn’t installed square, then when the bifold doors are closed into a screen, gaps will be different from one end to the other, as the set, and doors have to be square. In this instance, if you have a system with a low level threshold (like the Roomfold Deluxe range) you can pack under the threshold track to ensure the set operates properly. If you have a system without a base track, you may have to install a fixed threshold underneath the doors to make the gap look even, which you can lay your flooring up to either side.

I can see from the image on screen that your access door is on the right hand side. We need a set with the access door on the opposite side, can this be done?

ANSWER – Yes, all of our bifold door sets are fully reversible. The way you install the frame decides which room the doors fold into, and the way you fit the hardware to the doors decides which side the doors fold to – these sets are fully universal.

Do your interior bifold doors fold back against the adjacent wall?

ANSWER – no they don’t. The nature of a bifold door is that the doors are connected into an overhead base track, so they will only ever fold to 90 degrees to the face of the wall (however we do have our french folding door system which allows the doors to fold back flat against the wall).