Guides · Fitting
Fit your new door after delivery
Fitting a uPVC or composite door set is within reach of a competent DIYer — the frame goes in much like a window. The difference is the weight of the slab and how unforgiving a door is of anything out of level or plumb. Budget a full day, get a helper, and read the whole guide before the old door comes out.
Not confident? Hire a professional installer
These guides are written for competent DIYers. Fitting windows and doors involves heavy glass, working at openings and getting things level, plumb and sealed — if you are unsure at any point, hire a professional installer. In England & Wales, replacement windows and external doors must comply with Building Regulations: an installer registered with a competent-person scheme (such as FENSA or Certass) can self-certify the work, while DIY installations should be notified to your local building control. Glass units and door slabs are heavy — always work with a second person, wear gloves and eye protection, and never let a frame or glass unit take the weight of the wall above.
Questions about your order or fitting? Get in touch — we're happy to talk it through before you start.
What you'll need
- · Tape measure & spirit level
- · Drill, masonry bits & frame fixings
- · Flat packers & glazing packers
- · Allen keys (hinge adjustment)
- · Old saw & pry bar (for the old frame)
- · Low-expansion foam & silicone + gun
- · Mortar if the base needs making good
- · Gloves, eye protection & a helper
- 1
Check the door set and the opening
Unwrap and check the door against your order, and check the opening: the outer frame wants roughly 10mm total clearance (about 5mm a side) and a sound lintel above — the frame never carries the wall. Think about the finished floor level inside and out so the threshold ends up where you want it. And be honest about the weight: a glazed uPVC slab is heavy and a composite slab heavier still — this is a two-person job.
- 2
Remove the old door and frame
Take the old slab off its hinges first — never saw a frame with the door still hung. Then cut through the head and both jambs, lever the sections inwards with a pry bar, and lift out the old threshold. Protect the plaster reveal and the damp-proof course as you go, sweep the opening clean and pull any old fixings and mastic.
- 3
Prepare a solid, level threshold base
The threshold is the foundation of the whole door — it must sit on a clean, solid and level base with no voids or rubble. Fill hollows with mortar and let it set rather than relying on packers alone. When you're ready to fit, lay a generous bed of silicone under the threshold line so water can never track beneath it. Check level along the threshold and front-to-back: a door copies every millimetre of error at the bottom.
- 4
Stand the frame and plumb it
Take the slab off its hinges (flag hinges unclip once the caps are off) and stand the empty outer frame on the threshold — far lighter and easier to handle. Pack between frame and wall at the hinge heights on one jamb and the keep heights on the other, then work the frame plumb in both directions with equal diagonals. Don't rush this: a frame that's a few millimetres out of plumb becomes a door that swings open or shut on its own.
- 5
Fix the frame
Fix through the jambs with frame fixings close to each hinge and each keep — those are the points that carry load — keeping to the usual rules: 150–250mm from corners, no more than 600mm between fixings, and a packer behind every screw so the profile can't bow. Screw the threshold down into the base and seal every threshold screw head with silicone. Re-check plumb and the diagonals after each fixing goes in.
- 6
Hang the slab and set the margins
Re-hang the slab and stand back: the gap between slab and frame should be even all the way round (roughly 3–5mm) and the door should close onto its seals with a gentle push, latching without force. Modern flag hinges adjust in height, side-to-side and compression with an Allen key — small turns, test between each. The lock keeps on the frame can also be adjusted to fine-tune how snugly the door pulls in.
- 7
Toe and heel glazed doors
A glazed or panelled uPVC door relies on its glass to stay square, so it must be toe and heeled: packers between glass and slab at the bottom hinge corner (heel) and the top lock corner (toe), exactly as in our toe & heel guide. Ours leave the factory packed, but check it after fitting — handling can shift things. Composite doors have a solid slab, so skip this step and do any squaring on the hinges instead.
- 8
Seal, then test everything
Fill the frame-to-wall gaps with low-expansion foam, trim when cured, and run a neat external silicone bead all round — without ever sealing over the threshold drainage. Fit internal trims and peel off the protective tape. Finally, test properly: operate the lock with the door open first (so a misaligned keep can't trap you), then closed; try both keys, lift the handle, and check the seals compress evenly. A door that needs slamming today will need a locksmith later — adjust it now.