Guides · Fitting

Fit your new bifold doors after delivery

Bifolds go in like a very wide door: a dead-level cill, then the made-up set — leaves already hung — stood on it, squared and fixed to the outer wall, and the leaves checked so they glide. It's a job for a confident DIYer with helpers, or for your own installer. Budget a full day — more for a wide set — and read this whole guide, and the manufacturer's instructions, before the old doors come out.

1. 1

   Check the delivery, the opening and the lintel

   Unwrap and check every part against your order before the old doors come out — the frame, each leaf, the cill and the hardware. Then check the opening: the frame should be about 10mm smaller than the brick opening each way (roughly 5mm a side), all four sides plumb and square, and the brickwork sound and free of loose mortar and dust. The lintel must be level and strong enough to carry the wall above and the doors themselves — the leaves run in a track at the head, so a sagging lintel will stop them moving. Making the opening wider is structural work: get that done, and signed off, first. Your bifolds arrive made up, with the leaves already hung on the frame, so the whole set is heavy: plan on enough people to lift and carry it as one unit without twisting it, with the leaves kept closed and shoot-bolted.

2. 2

   Remove the old doors and frame

   Take the old doors, sliding panels and glass out first — never cut through a frame with glass still in it. Then cut through the head, jambs and threshold, lever the sections out with a pry bar, and pull any old fixings and mastic. Protect the plaster reveals and the damp-proof course as you go, and clean the opening back to sound, dust-free brickwork.

3. 3

   Prepare a level base and fit the cill

   The cill and threshold carry the whole set, so they need a solid, level base along the full width — firm enough to take packers every 250mm and fixings every 600mm. Lay a damp-proof layer under the cill, turned up 150mm at each side of the opening and lapped into the wall's existing damp-proof course. Bed the cill on mortar if the base is uneven (if it isn't, seal along its edge with silicone) and get it level to within ±1mm per metre with a 1.8m level or a laser. Fix it through the centre of the thermal break, 150mm from each end and no more than 600mm apart, with a little silicone on every fixing, then run silicone along both ends and the inner edge of the upstand.

4. 4

   Stand the doors on the cill and square the frame

   There's nothing to take apart: the leaves come already hung on the frame and set up at the factory, so leave them on. Keep them closed, shoot-bolted and locked while you work, so the set stays square and nothing can swing open. Lift the doors onto the cill as one unit, then pack under the jambs and down both sides until the frame is plumb, level and square, with the diagonals equal to within 1mm.

5. 5

   Fix the frame

   Fix into the outer leaf of the wall — never over an open cavity. Drill and fix 150mm from each end and no more than 600mm apart, all round, with a packer at every fixing so the profile can't bow. On the jambs, take the cover trims off to fix through the centre of the thermal break, then clip them back on. In the threshold, every screw head must sit below the bottom of the track so the rollers can't hit it, and every bottom fixing must be sealed against water. Re-check level, plumb and the diagonals as each fixing goes in.

6. 6

   Check the leaves, then the locks

   The leaves are set up at the factory, so they should need little or no adjustment. Once the frame is fixed, check the gap between each leaf and the frame is equal above and below — Sheerline specifies 12mm (±1mm). Only if a leaf has moved in transit, adjust its rollers: single and double rollers turn opposite ways for up and down, so check the instructions supplied with your doors before you turn anything, and hinge packers can square up a leaf that's slightly out. Then check the latch and the lock keeps: the doors should close and lock with a gentle push — never force a handle. Fit the magnets that hold the folded leaves open, if they aren't already on. If your glass comes separately, glaze each leaf following those instructions: bifold glass is packed (toe and heeled) to a pattern that depends on the layout, and that packing is what keeps each leaf square — our toe & heel guide explains the idea.

7. 7

   Seal, finish and test everything

   Break off any packers that stick out. Fill bigger gaps between frame and wall with low-expansion foam — don't overfill — then trim, run a low-modulus, neutral-cure silicone round the outer frame and seal below the cill. Never seal over the threshold drainage. Peel off the protective tape and clean the aluminium and glass with warm, soapy water. Then test properly: fold every leaf open and closed, check the master door opens on its own, the locks engage without force and the magnets hold the stack open. A leaf that needs forcing today needs adjusting now.