How To Frame A Bifold Door

Internal bifold doors are a little trickier to install than the other sorts we might find in our home.  Not only do they require rails, runners, and other extra components, but they come in a range of different sizes that require a range of different frames.  If you’re installing a bi-fold door, then you’ll likely be replacing an older door frame, or creating a space from scratch, rather than modifying an existing frame.

Please be aware that we aren’t going to discuss how to knock out walls for a larger set of folding doors – that’s a job that’s far more risky and advanced than what we’re talking about here, and one that should be performed by (or at least, after close consultation with) an expert builder or carpenter.

With that in mind, let’s take a look at how to frame a wall for bifold doors.

How to Frame a Bifold Door: Step-by-step Instructions

Let’s go through the entire procedure, step-by-step.  

Remove the old frame

If there’s already a frame installed, you’ll need to get rid of it before proceeding.  Do this by first getting rid of the outer casing – the decorative bit which hides the frame itself.  You’ll want to do this with a chisel or crowbar – but it’s best to first cut around the frame with a Stanley knife to create the initial gap.  Then carefully work your way around the frame, bringing it slowly loose until it comes away easily.

The old frame will now be visible.  If it’s been installed competently, it will be attached to the surrounding wall with a series of nails and screws.  Remove these and then remove the frame.  You should now be looking at fresh opening that’s ready to have a door installed into it.  Well, almost ready – next we need to measure it.

Measurement

You’ll want to take ten measurements.  Start with the two diagonal measurements from top left to bottom right, and from top right to bottom left.  These two should match up closely if the opening is square; if they don’t then you’ll need to adjust the frame to compensate.  Next, you’ll want to measure the width and height of the door.  Do this by taking three measurements of each – down the left, centre and right of the door, and across the top, middle and bottom.  Ideally, these three measurements should be close together. Use the lowest of each three when shopping for replacement doors.

You’ll want your door frame to be a few millimetres wider than the finished door.  This will allow for any small irregularities in the final framing.  The closer this tolerance, the more likely you’ll be to run into problems with the door catching on the frame later on – have it too wide, however, and you’ll have a draughty door.

Cut the head and cover pieces to size

Cut the various pieces of the frame down to the appropriate size.  You’ll find a table of these sizes listed in the instructions that came with your door.  The jamb height should be 2048mm to suit 1981mm-tall doors, but if yours are non-standard you’ll need to adjust accordingly.  The jambs are the ones that don’t have a recess in them- the recessed pieces are there to fit the top and bottom rails and disguise the runners.

It’s an extremely good idea to put the bottom three pieces into the doorway before proceeding, so that you can get the best possible idea of how the door will fit.  Use your plumb and spirit level to ensure that the jambs are truly vertical, and then put the top piece on.  Be careful when doing this – you obviously don’t want any piece of the frame to fall on your head.

Assemble the frame

Once you’ve established that the frame matches the hole, you’ll be able to get on with the business of putting it together.  Use a 5mm drill bit to make two holes at the very end of the front head.  These will later accommodate the screws that’ll hold the door together.  These holes should be parallel to the short end of the head, 12mm away from each side and 15mm from the end.   

Having done this, you’ll want to do the same to the end of the jamb that’ll attach.  Do this with 3mm bits to a depth of around 75mm, drilling through the holes you made in the front head to ensure that they line up properly.

Repeat this procedure for both top corners of the frame.  You should still be left with the cover for the track on the other side – the back head.  This should be attached only at the end of the installation – as it’ll only get in the way as you put the doors into position.

Affix the frame to the walls

Once you’re certain that everything is accurately square and plumb, you’ll be able to secure the frame to the opening and move onto installing the track and the doors themselves.  Do this using nails at regular intervals around the outer edge of the frame.  Use shims to plug any gaps, and don’t start nailing until you’re certain everything is properly aligned.

Additional Tips

Once you’ve got the frame into position, ensure that it really is accurately installed before moving on.  If the diagonal measurements of your frame aren’t within a few millimetres of one another, then you’ll want to stop and make the appropriate adjustments.

Suffice to say, installing a set of bifold doors isn’t a one-person job.  If you’re just installing a small set for a cupboard, you might be able to go it alone – but you’ll likely do a better job with the help of a friend.

In conclusion

Installing a folding door might seem a fiendishly complicated task, but it’s something that an experienced DIY enthusiast should have little trouble getting to grips with.  If you’re at all unsure of your skills, however, it’s probably best to get your bifold patio doors professionally installed.