Most people get bi-fold doors wrong at exactly the wrong stage.
They pick the doors. They finalize the layout. They’re already imagining summer evenings with the whole back of the house open.
Then the structural engineer takes one look and says: “Those doors won’t work with that beam.”
Now you’re stuck with:
● Doors on order that won’t open properly
● A lintel that needs upgrading to a steel beam with bottom plate
● Or both
The problem? One detail that nobody thinks to check until it’s too late.
Top-hung or bottom-rolling?
That’s it. That’s the question that changes everything structurally.
Bi-folds rely on a track. Where that track sits – top or bottom – completely changes what the beam above needs to do.
Most people assume “the beam just holds up the wall.” With bi-folds, that’s only half the story.
Here’s what actually matters:
Bottom-rolling doors: They carry their own weight
With a bottom-rolling system, the door panels sit on a track at floor level. The doors support themselves downwards into the floor. The top track? It’s just there to keep them aligned.
What that means for your lintel:
● It still needs to support the wall, roof, or upper floor above (like any opening would).
● But it doesn’t have to “hang” the doors.
● The door is less fussy about tiny movements in the beam.
Top-hung doors: The beam becomes part of the door system
With top-hung doors, the panels hang from the head track. That means your beam isn’t just holding up the building anymore. It’s holding up the doors too.
And here’s where it gets messy.
The problem isn’t strength. Most beams are strong enough.
The problem is deflection – how much the beam sags under load, even slightly.
If your beam deflects even a few millimeters:
● The track drops out of line
● The door panels start to jam
● The smooth glide becomes a sticky drag
● In the worst cases, the doors won’t open at all
You’ll have an opening that’s structurally sound but operationally useless. The beam passed the safety checks. But the doors fight you every time you use them.
This is the expensive surprise
You thought you were getting a cavity lintel. Then your engineer tells you it needs to be a fabricated steel. Now you’re reworking ceilings, boxing in steelwork, or accepting visible structure you never wanted.
When it works (and when it doesn’t)
A lintel setup tends to work well when:
● You’re using bottom-rolling doors and the head is just guiding, not carrying
● The span is modest and you’ve got good support at both ends
A beam with bottom plate setup tends to work well when:
● The doors are top-hung and the opening is wide (more width = more deflection)
● You’ve got heavy loads above (another storey, big roof loads)
Real example:
Recent project in Warwick. Client wanted 4.5m of bi-fold doors across the back of their kitchen. Top-hung system, already ordered.
We ran the calcs. The “standard” lintel they’d been quoted would’ve deflected 20mm under load. Doesn’t sound like much. But it was enough to guarantee the doors would jam.
Solution? We moved to a beam and bottom plate solution. Extra cost: £450 in fabrication plus 1-2 weeks waiting for the steel to arrive. But the alternative was £4,000 of bi-fold doors that wouldn’t work.
That conversation happened 1 week before install. One month earlier and we could’ve switched to bottom-rolling doors with an off-the-shelf cavity lintel – no fabrication wait, no custom steel, just a standard spec that would’ve been on site in 48 hours.
Bottom line
The door system and the beam are not separate decisions.
Pick one without thinking about the other, and you’ll either blow the budget or end up with doors that stick.
The engineer cost? Same whether you call early or late. The difference? Get us early and we optimise. Get us late and we fix mistakes – at a premium.
Ready to get your bi-folds scoped properly?
We’ve worked on 1,000+ residential projects across the Midlands. Extensions, internal alterations, new builds.
We guarantee Building Control approval. We deliver in 7-10 working days. And we’ll tell you if your door choice is going to cause you problems before you’ve spent the money. Get in touch – we’ll contact you within 24 hours.
