Quick answer
A sagging composite door - where the corner opposite the top hinge dips and starts scraping the frame or threshold - is almost always a loose or worn top hinge, since it carries the greatest share of the door's weight. Most cases are fixable with a hinge adjustment or replacement rather than needing a new door slab, typically £75-£320 depending on severity.
Overview
Sagging = the door corner opposite the top hinge is dropping. Usually top hinge loose, worn, or the door has never been adjusted since fitting.
Symptoms
- Latch corner scrapes the frame or threshold.
- Visible tilt.
Common causes
- Loose top hinge.
- Worn top hinge.
- Poor original installation.
Why the top hinge takes the blame more than any other
A hung door works structurally like a horizontal beam supported at its hinge points, and because the bottom hinge (or a bottom pivot on some configurations) primarily resists the door swinging rather than carrying vertical load, the top hinge ends up bearing a disproportionate share of the door's actual weight. When fixing screws on the top hinge loosen, or the hinge's internal pin and bush wear, that's the first point of failure in the overall support system, and the visible result is the door dropping at the corner furthest from that hinge - typically the top of the latch-side edge.
This is why almost every sagging-door diagnosis starts with the top hinge specifically, rather than treating all hinges as equally likely suspects, even though in principle any hinge could theoretically contribute.
Recognising sagging versus other alignment faults
Sagging has a fairly distinctive signature: a visible tilt to the door when viewed from the side or from directly in front with the door closed, a scraping sound or resistance as the latch corner drags against the frame or threshold, and often a widening triangular gap visible at the top of the hinge side as the door pivots slightly out of its original square shape within the frame. This differs from simple horizontal misalignment (where the whole door has shifted sideways but remains square) or seasonal swelling (where the door binds evenly around its whole perimeter rather than tilting).
Photographing the door from a few angles when you first notice the issue is genuinely useful - it gives a baseline to compare against if the sag worsens over subsequent weeks, which helps distinguish a sudden hinge failure from a slow, gradual drift that's been building for longer than you realised.
Diagnosing loose versus worn
A loose top hinge - where the fixing screws have simply worked free from the frame or door core - is the more straightforward and cheaper of the two underlying causes, and often visible on close inspection as slightly proud screw heads or a small gap opening between the hinge leaf and the surface it's fixed to. A worn top hinge - where the pin and bush have degraded internally - won't necessarily show any obvious external sign, and its presence is usually confirmed by attempting an adjustment and finding the door drops back out of position again within days or weeks.
This is a meaningful distinction because a loose hinge is fixed by simply re-tightening or re-fixing the screws (occasionally with a larger screw or thread insert if the original holes have stripped), while a worn hinge needs replacing entirely, since no amount of tightening restores worn internal components.
Why very few sagging doors need a new door slab
It's a common worry that a visibly sagging door means the slab itself has warped or the frame has failed structurally, but in the overwhelming majority of cases we attend, the door slab and frame are both entirely sound, and the fault is confined to the hinge hardware supporting them. Composite door slabs are specifically manufactured to resist warping far better than solid timber doors, using a rigid foam or timber composite core within GRP or similar skins, which is one of the material's genuine advantages for this specific failure mode.
Only in cases of serious impact damage, prolonged and severe water ingress into the door core, or a very poor original installation with an out-of-square frame, would we expect the underlying door or frame itself to need attention beyond the hinges.
The repair process for a sagging door
The first step is always checking and tightening the top hinge's fixing screws, since if this alone resolves the sag, it's the cheapest possible outcome and requires nothing further. If screws are already tight or re-tightening doesn't hold, vertical cam adjustment on the hinge itself (assuming it's an adjustable type, as almost all modern composite door hinges are) is attempted next, correcting the drop directly through the hinge's built-in adjustment range. Only where the hinge has reached the limit of its adjustment range, or where testing shows it's genuinely worn internally, does replacement become necessary.
Throughout this process we support the door's weight properly rather than letting it hang unsupported from a single hinge while working, since a door left unsupported during a hinge repair is at real risk of dropping further or damaging the frame.
Preventing recurrence
Once a sagging door has been corrected, an annual check of all hinge fixing screws - simply confirming they're still tight with a screwdriver - catches the early loosening that leads to sagging before it progresses to a visible tilt. For coastal properties, this check is worth doing more frequently given the faster corrosion rates discussed on our rusty hinges page, since a corroding screw thread can work loose faster than a simple vibration-driven loosening would on an inland property.
How sagging compounds into lock and seal failure
A sagging door rarely stays a single, isolated problem. As the door drops slightly at the hinge side, the multi-point hooks no longer meet their keeps squarely, which increases resistance on the handle and gearbox with every use. At the same time, the door's fit against the frame changes, compressing seals unevenly on one side while leaving gaps on the other, which affects both draught-proofing and water resistance.
Left long enough, this combination - harder locking action, uneven seal compression and increasing hinge wear as the remaining hinges compensate - tends to accelerate rather than stay stable. A sag that could have been corrected with a straightforward hinge adjustment early on can, after a year or two of continued use, require hinge replacement and gearbox attention together.
Diagnosing sag versus frame or wall settlement
Not all apparent door sagging originates at the hinge. Occasionally what looks like a sagging door is actually the surrounding frame or the wall it's fitted into settling slightly, particularly on newer builds still experiencing normal structural settlement in the first few years, or older properties with historic movement. Distinguishing between the two matters because hinge adjustment won't correct a frame that's genuinely out of square.
A simple check is to measure the gap between door and frame at several points around the perimeter - if the gap is roughly even but simply too tight or loose all round, that points towards hinge-side sag; if the gap varies dramatically from top to bottom on one side specifically, frame movement is more likely and needs a different assessment.
Coastal conditions and accelerated sag
Coastal properties see hinge-related sag develop somewhat faster than inland equivalents, largely because salt exposure accelerates the corrosion of hinge pins and fixing screws that hold the hinge to both door and frame. A hinge that's corroding internally provides less consistent support over time even before it's visibly failing, which contributes to gradual sag that might otherwise take longer to develop.
For exposed coastal properties, we'd suggest treating any new sag as worth checking sooner rather than later, since the same corrosion contributing to the sag is also likely affecting the hinges' remaining service life, and an adjustment-only fix may have a shorter effective lifespan than the same fix on an inland property.
Typical repair paths and what determines cost
Where sag is caught early and is purely a hinge alignment issue, a straightforward 2D or 3D hinge adjustment is often sufficient and is one of the more affordable interventions available. Where hinges have already worn to the point that adjustment alone won't restore proper alignment, replacement of the affected hinge or hinges is needed, and where sag has been present long enough to affect the multi-point lock's hook alignment, a gearbox check and possible keep adjustment are needed alongside the hinge work.
The overall cost is driven far more by how long the sag has been left unaddressed than by the door itself, which is the core reason we'd encourage early reporting over a wait-and-see approach.
What to tell us when booking a sagging door visit
Useful details include how long the sagging has been noticed, whether it's got worse recently, whether the door drags on the frame or floor, and whether the lock has become harder to use alongside the visible sag. Photos of the gap between door and frame at the top, middle and bottom on the hinge side are genuinely useful for us to assess likely cause before the visit.
For landlords and holiday-let owners, a sagging door reported by a tenant or guest is worth treating as reasonably urgent rather than a routine maintenance item, since the combination of harder locking action and uneven seals can affect both security and weatherproofing if left through a full letting season.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Top hinge re-fix and tighten | £75-£100 | Where screws have simply worked loose |
| Vertical hinge adjustment | £75-£120 | Where hinge is sound but needs recalibrating |
| Top hinge replacement | £90-£150 | Where adjustment doesn't hold or wear is confirmed |
| Full hinge set replacement plus adjustment | £240-£320 | For older doors with wear across all hinges |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- Hinge replacement or refit.
Prevention
- Annual screw check.
