Quick answer
A composite door rubbing at the bottom is nearly always caused by the top hinge having dropped, tipping the whole door down at the latch corner, though a raised or damaged threshold is also possible. It shows up as scrape marks and wear on the threshold and should be corrected by hinge adjustment, never by planing the door itself.
Overview
Rubbing at the bottom is almost always a dropped door - top hinge worn or loose, latch corner sags down. Occasionally the threshold has been kicked up or a screw has worked proud.
Symptoms
- Scrape marks on the threshold.
- Door bottom wearing.
Common causes
- Top hinge dropped.
- Threshold screw proud.
- Threshold damaged.
Why the top hinge is usually to blame for a bottom problem
It seems counterintuitive that a problem at the bottom of the door is caused by hardware at the top, but that's exactly how it usually works. The top hinge carries a disproportionate share of the door's weight and leverage, and when it wears or loosens, the entire door pivots downward at the opposite corner — the bottom of the latch side — because that's the point furthest from the remaining support.
This is why an experienced installer checks the top hinge first on a bottom-rubbing complaint, even though it feels backwards. Tightening or adjusting the top hinge often resolves bottom rubbing without touching the bottom hinge or the threshold at all.
Distinguishing a dropped door from a threshold problem
The second possible cause is entirely different: the threshold itself has been damaged, has a screw working proud, or has shifted slightly, physically raising a section of the door's path and causing contact regardless of hinge condition. This is more common after a heavy impact — a dropped object, a piece of furniture dragged across it, or storm debris — than from gradual wear.
The way to tell the two apart is straightforward: if the door rubs consistently along its full bottom edge, hinge drop is the likely cause. If it rubs only at one specific point along the threshold, regardless of how the door is adjusted, a localised threshold defect is more likely.
- Rubs along the full bottom edge: check the top hinge for drop or wear.
- Rubs at one fixed spot only: check for a proud screw or damaged threshold section.
- Rubbing has gotten worse gradually over months: hinge wear, most likely.
- Rubbing started suddenly after an impact: threshold damage, most likely.
Why you should never plane or sand the door bottom
It might seem like the obvious fix for a rubbing door bottom is to remove a sliver of material so it clears the threshold — this is standard practice on timber doors, but it is genuinely damaging on a composite door. Composite slabs have a GRP (glass-reinforced plastic) outer skin bonded over an insulating core, often with a timber sub-frame around the edges. Cutting into that skin exposes the core to moisture ingress permanently.
Once water gets into a composite door core through a cut edge, it can cause swelling, delamination of the skin, and eventually structural failure of the slab — a problem that no amount of hinge adjustment can then fix, and one that will void any manufacturer warranty immediately. The gap should always be corrected by moving the door, not by removing material from it.
Thresholds and Cornwall's wet-weather exposure
Aluminium thresholds are standard on most composite door installations and are generally very durable, but on exposed coastal properties they take a battering from grit, sand, and standing water during storms that inland properties don't see nearly as much. We regularly find thresholds with debris packed into the drainage channel, which can cause water to sit against the door bottom and, over time, contribute to swelling of the door's lower edge even without a hinge fault present.
Clearing and inspecting the threshold drainage channel is a five-minute check worth doing as part of any bottom-rubbing diagnosis, particularly at Cornish properties near the coast where sand ingress is a genuine, regular occurrence rather than a rare event.
What we check and adjust on a bottom-rubbing call-out
A methodical visit starts by checking all hinge screws for tightness, followed by measuring the reveal at the bottom corner specifically to quantify how much correction is needed. We then check the vertical adjustment cam on the top hinge, correct in small increments, and re-test the door's swing and closing action after each change before moving on to the threshold itself.
If the threshold is the culprit, the fix is either clearing debris and resealing the drainage channel, or in cases of physical damage, replacing the affected threshold section — a bigger job but still generally a single-visit repair.
A case from a farmhouse near Wadebridge
A farmhouse conversion near Wadebridge had a composite door dragging heavily along the bottom, loud enough that the owner assumed the whole door had swollen. On inspection the top hinge had dropped by around 3mm — enough to tip the bottom latch corner down into contact with the threshold — while the threshold itself was in good condition. A vertical adjustment at the top hinge lifted the corner clear, and the drag disappeared entirely without any work needed at the bottom of the door at all.
Why timing the call-out around the seasons helps with bottom-rub cases
A door rubbing at the bottom shows one of the clearest seasonal patterns of any composite door fault, because the threshold and lower rail sit closest to ground-level moisture, splashback from rain, and — on Cornish coastal paths — salt-laden damp air that rises off nearby ground. We see the sharpest spike in bottom-rub reports in late autumn and midwinter, when ground moisture is highest, and a corresponding easing off through a dry summer. Booking a repair visit during the wet peak, rather than waiting for a dry spell, means we can see and measure the rub at its worst rather than a temporarily improved version of the problem.
Frame and threshold fixings in granite and cob settings
Thresholds fixed into granite door sills are extremely stable once set, but the sill itself can develop a very slight camber over decades of weathering, meaning the middle of the threshold sits a fraction higher than each end — enough, over a wide door, to cause bottom-rub only in the centre of the swing. On cob and older rendered openings, ground-floor thresholds are more prone to gradual settlement as the wall base absorbs and releases moisture seasonally, which can tip a previously level threshold enough to cause rubbing that wasn't there when the door was first installed.
In both cases, a hinge adjustment lifting the whole door slightly can compensate, but if the threshold itself has developed a genuine slope, packing or resetting the threshold is the more durable fix.
How bottom-rub gets worse if it's left
A door dragging along its threshold wears through the bottom rail's protective finish faster than almost any other point on the door, because the bottom edge often sits in standing moisture from rain or cleaning runoff. Once the GRP or composite finish is breached at the bottom rail, the exposed core is directly exposed to ground-level damp, and composite door cores — while more resistant than solid timber — can still swell, discolour, or in prolonged cases delaminate at the point of damage.
What starts as an audible scrape that's mostly a nuisance can, within a season or two of being ignored, become a bottom rail repair or in severe cases a full slab replacement, which is a dramatically more expensive outcome than the original hinge lift would have been.
When adjustment can't fully solve a bottom rub
If the door has already been lifted to the top of its available vertical hinge travel and it's still rubbing, there's no more height to give from the hinge side, and the fix has to move to the threshold or the door's lower rail itself — either packing beneath the threshold, planing the fractional amount of clearance needed on a factory-finished edge by a specialist, or in rare cases fitting a slightly adjustable threshold seal designed to accommodate small ongoing seasonal movement.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Top hinge vertical adjustment | £75–£120 | Resolves the majority of bottom-rubbing cases |
| Threshold debris clearance and reseal | £75–£100 | Where drainage channel blockage is the cause |
| Threshold section replacement | £150–£280 | Needed where the threshold itself is damaged |
| Combined hinge and threshold assessment | £95–£130 | Recommended if the cause isn't obvious from outside |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- Threshold needs replacing.
Prevention
- Don't sit heavy items on the open door.
