Quick answer
Replace rather than repair a composite door when water has damaged the timber core, the frame is beyond re-fixing, the U-value is badly dated (pre-2010), the security spec can't reasonably be brought up to standard, the appearance is beyond restoration, or realistic repair costs exceed roughly 60% of a full replacement. Anything short of these is usually better addressed with a repair.
Overview
Replacement is right when: slab damage compromises the timber core; frame is beyond re-fixing; U-value is dated (pre-2010); security spec is unfixable; aesthetics are past restoration; or repair cost exceeds 60% of replacement.
Symptoms
- Water damage into the timber core.
- Cracked or crushed slab.
- Frame beyond re-fixing.
- Pre-2010 U-values.
- Persistent security failures.
Common causes
- Age, damage, poor original spec.
The six genuine triggers for replacement
It's tempting to think of replacement as the 'safe' default when a door has multiple problems, but in most cases it's an expensive overreaction to issues that repair handles perfectly well. There are, however, six specific situations where replacement genuinely is the sensible answer, and recognising them clearly avoids both premature replacement and, just as wastefully, throwing repair money at a door that's past the point of being worth it.
These six triggers are: timber-core water damage, a frame beyond re-fixing, seriously outdated thermal performance, an unfixable security shortfall, appearance beyond restoration, and a repair cost that exceeds around 60% of what a full replacement would cost. Meeting one of these clearly is usually enough on its own to justify replacement; meeting several together removes any doubt.
Water damage into the timber core
Many composite door slabs are built around a timber core for rigidity and insulation, wrapped in the GRP or composite skin that gives the door its weather resistance and low maintenance finish. If water has been getting past a failed seal or gap for long enough to reach that core, the timber can swell, rot, or delaminate from the outer skin — and once that's happened, no amount of external repair restores the door's structural integrity.
This kind of damage often isn't visible from the outside until it's fairly advanced, showing up instead as a slab that feels slightly soft in one area, or a corner that's begun to distort. If you suspect this, it's worth having it properly assessed rather than continuing to treat surface symptoms.
A frame beyond re-fixing
Most frame movement and fixing problems are repairable, as covered elsewhere on this site, but there's a point past which re-fixing isn't viable — typically where the surrounding masonry has crumbled extensively, where the frame section itself has been distorted by prolonged movement, or where the original frame was simply the wrong size for the opening in a way that packing can't permanently solve. In these cases, a proper refit with a correctly specified new frame is the only route to a genuinely lasting fix.
Dated U-values and Part L compliance
Thermal performance standards for external doors have tightened meaningfully since around 2010, and a door installed before then is very likely to have a noticeably worse U-value than current Building Regulations Part L standards call for on new installations. This matters both for ongoing heating costs and, if you're doing other work to the property that triggers a Part L assessment, for compliance more broadly.
This isn't usually a decisive factor on its own — an older door with a dated U-value that's otherwise sound and well-maintained can reasonably stay in service — but combined with other issues, it tips the balance more firmly towards replacement rather than investing further in repair.
Security specification that can't be brought up to standard
Older doors sometimes have a security specification — cylinder type, lock mechanism, glazing method — that falls short of current Part Q and PAS24 expectations in ways that can't be resolved through component upgrades alone. A door with externally accessible glazing beads built into the slab design itself, for example, can't be retrofitted to internal beading without effectively remaking the door. Where the underlying design is the limiting factor rather than a single replaceable part, replacement becomes the only way to properly close the gap.
Appearance beyond restoration, and the 60% rule
Fading, deep scratching, or finish degradation that's gone past what waxing, polishing or colour restoration products can address is a legitimate, if less urgent, reason to consider replacement — particularly for a front door that matters for kerb appeal, such as on a holiday let where first impressions affect bookings. This trigger alone rarely demands immediate action but is worth factoring in alongside other considerations.
The clearest practical test, though, is the 60% rule: total up realistic repair costs for all outstanding issues and compare that figure against a full replacement fitted from £1,395. If repairs come in above roughly 60% of that replacement cost, you're spending heavily to extend the life of a door that's already accumulated enough separate problems to suggest it's reaching the end of its useful life anyway.
Getting an honest comparison
Because the six triggers above require different kinds of assessment — structural, thermal, security, cosmetic and financial — the most reliable way to decide is a proper on-site assessment that checks each one specifically, rather than judging from a general impression that the door 'seems old' or 'has had a few problems'. We provide straight answers on this, including quoting realistic repair costs alongside a replacement quote so you can apply the 60% rule yourself with real numbers rather than guesswork.
A numbers-based framework for the replace decision
As a working guide: if repair costs are below roughly 30% of a new door's price (from £1,395) and the frame tests structurally sound, repair. Between 30% and 60%, it's a judgement call based on the door's age and how many separate faults you're dealing with at once. Above 60%, or where the frame itself needs replacing alongside the leaf, a new door is almost always the better long-term value, since you're not paying twice to fix a frame and then again for a leaf that's ageing alongside it.
Age matters alongside cost: a composite door under 8 years old with an isolated fault is usually worth repairing; one past 15 years with multiple developing issues (seal wear, hardware fatigue, fading) is approaching the point where a new door's better thermal performance and warranty outweigh further repair spend.
Insurance-backed guarantees as part of the decision
A door still within a live insurance-backed guarantee period changes the calculation considerably, since a genuine structural or workmanship fault may be covered at no cost to you regardless of the repair's apparent value relative to a new door. Check any paperwork from the original installation before assuming a repair is coming out of your own pocket.
What replacement costs and what it includes
A new composite door from Cornwall Composite Doors starts from £1,395 fitted, including removal of the old door, a correctly sized and packed frame, full weatherproofing detail, and a CERTASS compliance certificate covering Part L and Part Q. That certificate alone is worth factoring in if your existing door was never properly certified, since replacement resolves that gap at the same time as the physical problem.
Second homes: the replace decision when you're not there day to day
For a second home or holiday let, ongoing repair visits carry a coordination cost beyond the invoice — arranging access, liaising with a keyholder, potentially losing letting days around each visit. Where a door has needed two or more separate call-outs in short succession, replacement often makes more practical sense for an absent owner than it would for someone on-site who can manage repairs more easily as they arise.
Servicing history as evidence for the decision
If you've kept any record of servicing or previous repairs, it's genuinely useful at this stage — a door with a clean service history and one isolated new fault is a very different proposition to one with a string of undocumented issues going back years. We're happy to review whatever records you have as part of a replace-or-repair assessment rather than starting from scratch.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Full condition assessment (all six triggers checked) | £45–£75 | Often credited against repair or replacement |
| Typical repair range for comparison | £75–£320 | Per issue |
| New composite door, fitted | From £1,395 | Includes disposal and compliance certificate |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- For a straight replacement quote.
Prevention
- Maintenance extends life - but nothing lasts forever.
