Bifold Door Lintel & RSJ Guide | Wade Building Supplies

If you’re opening up a wall for bifold doors, the support above the opening is your make-or-break decision. A lintel for bifold doors (or an RSJ steel beam above bifold doors) must control deflection to millimetre tolerances; even slight sag can cause the leaves to bind, drag in the track, or fail to close. Treat a bifold span as a structural alteration first and a glazing job second.

Why Bifold Doors Are Different

Wider spans: 3–6 m is common, far beyond typical window openings.
Higher loads: masonry, floors, and sometimes roof loads bear on the lintel above bifold doors.
Track sensitivity: doors need a dead-straight head — tiny deflections become operational problems.

For a broader overview of lintel functions and uses, see our guide: Door Lintels: A Detailed Guide.

Lintel, Custom Lintel, or RSJ?

Heavy Duty Lintels (off-the-shelf): viable on smaller spans and still an option up to 3.6 m with the right product (see Naylor Hi-Spec Lintels). Always check load tables and confirm with Building Control.
Custom Lintels: engineered to order for unusual spans or detailing. Note that custom Naylor lintels are typically limited to 4.8 m. Above that, you’re realistically into RSJ territory.
RSJs (Rolled Steel Joists): preferred once spans exceed 3.6 m, where loads are high, or where you want belt-and-braces stiffness. Browse our range of RSJ beams.

Top-Running vs Bottom-Running Systems (Why It Matters)

Bottom-running (most aluminium): weight sits on the floor track; the head support primarily carries wall/floor/roof loads.
Top-running (common in timber): door weight hangs from the head. This increases demand on the lintel/beam and often tips the choice towards an RSJ steel beam over bi-fold doors detail even at shorter spans.

What to Confirm Before You Order

Opening width & bearing: measure span and allow ≥150 mm bearing each end (e.g., 3.0 m opening → 3.3 m support length).
Door weight: aluminium is heavy, timber heavier; total leaf weight adds to the load when closed.
Wall build-up: single leaf, cavity, or solid; identify loads from floors/roof.
Masonry above: lightweight block vs brick/stone, plus height of masonry over the opening.
Track system: confirm top- or bottom-running with your door supplier before finalising the support.

Handling & Safe Lifting (Real-World Weights)

3.0 m heavy-duty lintel: typically ~50–70 kg.
4–5 m RSJ: easily 100 kg+ (plan mechanical lifting).

Kit you’ll likely need: acrow props with strongboys or needles, spreader boards, padstones/engineering bricks, a manual lift (e.g., Genie) for lintels/smaller steels, or a HIAB/site crane for larger RSJs. For supporting brickwork directly, consider a prop mate wall support.

If you’re interested in general installation techniques, see our related guide: How to Install a Concrete Lintel.

Installation Sequence (Contractor’s Method)

Set out: mark the opening; span + bearings. Double-check.
Temporary works: install acrows with strongboys/needles above the cut line; plumb and tighten onto spreaders.
Demolish to seats: remove masonry down to bearing level; clean and level. Fit padstones where specified.
Dry-fit: lift the lintel/beam into position to check seating and level across the full length. With 70 kg+, use a lifting frame — don’t brute-force it.
Bed & set: bed on mortar/padstones, ensure full contact, tap down with a timber block and hammer. Re-check level/line.
Reinstate & insulate: rebuild masonry, maintain cavity insulation and trays to avoid cold bridging, then remove temporary works.

Building Control & Regulations (Be Clear, Avoid Delays)

Planning permission: usually not needed for rear bifolds (exceptions: listed buildings, conservation areas).
Building Regulations: always required.

Crucial point: for very small spans (generally <2.4 m), Building Control may accept a heavy-duty lintel with the manufacturer’s specification sheet. In practice, most bifold sets are 3.0 m+, so expect to provide structural engineer’s calculations — especially for RSJs or where floors/roof loads bear on the opening. Rule of thumb: if it’s wide enough for a bifold, assume calcs will be required unless your inspector confirms otherwise in writing.

For a deeper dive into load capacity, see: How Much Weight Can a Concrete Lintel Support?

Contractor’s Tips (Sanity Checks!)

Control deflection: stiffer support = happier doors. Over-spec if you’re on the fence.
Level is everything: you can’t “pack it later” once the frames are in.
Thermal details matter: keep cavity insulation continuous; fit trays and damp-proofing per spec. Thermal bridging!
Top-running systems: bias towards RSJs even at modest spans.
Paperwork first: submit lintel/RSJ specs and calcs with your Building Notice to avoid site-day arguments.

Supply Options

Wade supplies heavy-duty lintels (including Naylor hi-spec lintels up to 3.6 m), custom lintels (typically available up to 4.8 m), and RSJs cut to size with certification. If you’re unsure, share your drawings — our team can match the support to your span, loads, and door system.

Conclusion

Bifold doors transform a space, but they’re only as good as the support above them. Choose the right bifold door lintel or RSJ steel beam over bi-fold doors detail, install it properly, and get Building Control on side early. Do that, and your doors will glide for years.

FAQ: Bifold Door Lintels

Do I need a steel beam above bifold doors?
: Often, yes. Heavy-duty/hi-spec lintels can work up to ~3.6 m depending on loads; beyond that, or where deflection tolerance is tight (top-running systems, heavy masonry), an RSJ is usually the safer choice.
Can Building Control approve without structural engineer’s calculations?
: Only on very small spans (typically <2.4 m) when you provide the lintel manufacturer’s spec sheet. For 3.0 m+ bifolds, expect calcs to be required.
How much bearing does the support need?
: Allow at least 150 mm bearing at each end and use padstones where specified by the engineer or manufacturer.
How heavy are lintels and beams for bifolds?
: A 3.0 m heavy-duty lintel is ~50–70 kg; a 4–5 m RSJ can exceed 100 kg. Plan mechanical lifting and safe temporary works. Acrows and Prop Mate supports are essential on site.
Are custom lintels an alternative to RSJs?
: Sometimes. Custom lintels (e.g., Naylor) can address specific spans/details, typically up to about 4.8 m. Above that, RSJs are the norm.