Quick answer
Replacing the glass in a composite door means fitting a new sealed unit into the existing beading, matching thickness, pane count and any decorative pattern to the original. It's a same-doorset repair, not a new door, and typically takes an hour or two on site once the correct unit has been measured and ordered.
Overview
Glass in a composite door is a sealed glazing unit held in place by internal beads. Replacement usually takes 30 minutes plus the wait for the unit to be manufactured (1-3 weeks typical).
Symptoms
- Cracked, smashed, misted or leaking glass.
Common causes
- Impact, thermal stress, seal failure.
When glass replacement is the right call
Composite door glass needs replacing when a unit has cracked, blown internally, or when a homeowner wants to upgrade an older single-glazed or poorly performing unit to modern standards. In all of these cases the slab, frame and hardware are unaffected and can be reused, which keeps the job to a fraction of the cost of a new doorset.
The main task is measuring accurately - height, width, thickness and bead type - so the replacement unit sits correctly in the existing rebate without needing the beading itself replaced.
How the beading system works
Composite doors hold their glazing unit in place with internal beading - strips of moulded material that clip or screw into the frame around the glass aperture from the inside. This is a deliberate security feature: beading fitted from the inside means an intruder can't simply lever the beading off from outside to remove the glass.
Removing the old unit means taking out the internal beads carefully, without damaging the finish, then lifting the failed unit free. New beads are occasionally needed if the originals have become brittle or damaged during a previous repair, but in most cases the same beading is reused.
Matching pane construction and appearance
A replacement unit needs to match the original in overall thickness so it sits correctly against the beading and seals properly, and ideally match pane count, spacer colour and any decorative glass pattern too. Decorative units - leaded, bevelled, sandblasted or coloured designs - need closer matching since a visible mismatch on a front door is far more noticeable than on a rear utility door.
We take full measurements and a photograph of the existing pattern where relevant so the replacement can be ordered as close a match as possible, even where the exact original design is no longer in production.
- Overall unit thickness for correct bead fit
- Pane count (double or triple)
- Spacer bar colour where visible
- Decorative pattern, leading or bevel style
Modern glazing specification
Replacement units are typically built with warm-edge spacer bars rather than older aluminium spacers, which reduces the cold bridge at the edge of the glass and cuts down on edge condensation. Most are argon-filled between the panes, which improves thermal performance over an air-filled cavity of the same thickness.
Toughened or laminated glass to BS EN 12600 is used depending on the door's location and local building regulations - critical locations near floor level or beside a door typically require impact-safe glazing, and we always specify to the correct standard for where the unit sits.
PAS 24 and security considerations
Where a door needs to meet PAS 24 security performance, the glazing unit forms part of that overall rating alongside the frame, hardware and locking system, so a replacement unit for a PAS 24 doorset should match the specification used in the original certified assembly rather than being an arbitrary equivalent thickness unit.
This mainly matters for newer doors where the whole doorset was tested as a system; older doors without a formal rating have more flexibility in the replacement unit chosen, though we'd always aim for at least equivalent security glazing.
What affects the cost
Cost is driven mainly by size, pane count, and whether the design is plain or decorative - a small plain double-glazed panel is at the lower end of the range, while a large triple-glazed or heavily leaded decorative panel sits at the top. Access and bead condition also play a small part, since brittle or damaged beading adds time to the job.
Lead times for decorative or bespoke patterns can run longer than for plain units, since these are often made to order rather than held in stock, so we'll always give a realistic timeframe alongside the quote.
The fitting process on the day
We remove the internal beading, lift out the failed or old unit, clean the rebate of old sealant or debris, and dry-fit the new unit before final bedding and re-beading. A final check confirms the unit sits square, the beading is fully seated, and there's no visible gap that could let water track in around the edge.
Most single-unit replacements are completed within one to two hours, and the door is fully usable again immediately afterwards with no drying or curing time needed before the door can be locked and used normally.
Cornwall-specific glazing considerations
Coastal properties benefit from slightly more robust glazing specification given the higher wind loading and salt exposure - argon-filled, warm-edge units generally perform more consistently over time in these conditions than older, cheaper specifications. Holiday lets in particular benefit from a durable, well-specified replacement since call-outs during a letting season are more disruptive to manage.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Standard double-glazed unit replacement | £120-£220 | Plain design, typical door aperture size |
| Triple-glazed unit replacement | £180-£320 | Higher thermal performance, added weight and cost |
| Decorative glass (leaded, bevelled, patterned) | £180-£380 | Bespoke or made-to-order designs cost more |
| Beading replacement (if damaged) | £30-£70 | On top of unit cost where original beads can't be reused |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- Always - beads must be reset correctly for security.
Prevention
- Ensure beads stay on the inside for security.
