Quick answer
Weatherproofing a composite door means checking every point around the perimeter that's designed to keep water and air out: the compression seal, the threshold, the drainage slots, and the frame-to-wall sealant. None of these are part of the slab itself, so weatherproofing work is almost always a targeted repair rather than anything to do with the door panel.
Overview
A full weatherproofing service takes about an hour and covers every element that keeps weather out.
Symptoms
- Any weather-related problem.
Common causes
- General wear.
What weatherproofing actually covers
A composite doorset relies on several separate systems working together to keep weather out, and each one can fail independently of the others. The compression seal handles the gap between the closed slab and the frame. The threshold gasket seals the underside of the door against the sill. Drainage slots at the base of the frame let any water that does get past the outer seal run away rather than pool. And the sealant joint between the frame and the surrounding wall stops water tracking in around the outside of the frame entirely.
A weatherproofing check goes through all four systematically, because a fault in any one of them can produce symptoms that look similar to the others - cold air, a damp patch, or water at the base of the door doesn't tell you on its own which system has failed.
The compression seal and threshold together
These two components take the brunt of day-to-day wear. The compression seal loses its spring over years of use and UV/salt exposure, while the threshold gasket wears from foot traffic and grit dragged in from outside. Because they're both rubber-based components under constant mechanical stress, they often need attention around the same time, particularly on a door that's several years old.
Checking both together, along with the multi-point mechanism's compression, is more efficient than treating them as separate callouts, and it means we catch a marginal seal before it fails completely rather than waiting for a second visit.
Drainage slots - the overlooked component
Every properly installed composite doorframe has drainage slots or weep holes at the base, designed to let any water that gets past the outer seal escape to the outside rather than sit in the frame cavity. These slots block surprisingly easily with wind-blown grit, moss, spider webs, or a coat of paint applied without masking them off during redecoration.
A blocked drainage slot can actually push water back inside the property during heavy rain, which sometimes gets misdiagnosed as a seal failure when the seal itself is fine. Clearing drainage slots takes minutes and costs nothing if it's found during a wider inspection, but it's easy to miss if you're only looking at the seal.
Sealant joints between frame and wall
The perimeter sealant - typically a flexible silicone or hybrid polymer bead - joins the outer edge of the frame to the surrounding masonry, render or brickwork. This isn't part of the door itself but its condition affects weathertightness just as much as anything on the doorset, and it's a common source of damp patches appearing on plaster to either side of the frame rather than at the base.
Cornwall's driven rain and wide temperature swings between winter storms and summer heat put more movement stress on sealant joints than a sheltered inland property would see, so we'd expect a coastal sealant joint to need attention somewhat sooner than an equivalent inland one.
Head drip cills and water diversion above the frame
A head drip cill is a small projecting lip fitted above the door frame, designed to throw rainwater running down the wall clear of the frame-to-wall joint rather than letting it track straight down onto it. On some installations this is missing, damaged, or was never properly sealed at the ends, and it's a common cause of water tracking down the wall from above the frame during heavy or wind-driven rain.
It's easy to overlook because it sits above eye level and isn't something most homeowners think to check, but it's one of the first things we inspect if water is appearing above rather than below the door.
BS 6375 and what weathertightness actually means
BS 6375 sets out weathertightness performance testing for doorsets, covering air permeability, watertightness and wind resistance under laboratory conditions. A doorset tested and rated to this standard has been checked under simulated wind and rain loading, but that lab performance depends entirely on correct installation and ongoing maintenance in the real world - a well-rated doorset with a failed seal or blocked drainage will still let weather in.
This is why weatherproofing isn't a one-off installation consideration but an ongoing maintenance need over the life of the door, particularly in an exposed coastal position where wind-driven rain routinely exceeds what a sheltered inland property experiences.
A typical weatherproofing service visit
We work through the door systematically: perimeter seal condition and compression, threshold gasket and drainage slots, multi-point mechanism adjustment, letterplate brush and flap, and a visual check of the external sealant joint and head drip cill. Most of this is diagnostic rather than replacement, and many visits resolve with adjustment alone rather than new parts.
Where something does need replacing, we'll always explain exactly which component failed and why, rather than replacing everything as a blanket precaution - it keeps the job proportionate to the actual fault.
Recommended checking frequency for Cornwall
For exposed coastal properties, an annual visual check covering seal, threshold and drainage is a sensible baseline, ideally ahead of the winter storm season when driven rain loading is at its highest. Sheltered inland properties can usually go two to three years between checks without issue.
Holiday lets benefit particularly from a pre-season check, since intermittent occupancy means minor faults often go unnoticed by guests until they become a booking complaint rather than a quick fix.
The case for proactive weatherproofing over reactive repair
Waiting until a draught or a leak is noticeable usually means the underlying component has already failed to the point of causing damage - a threshold gasket that's let water in over several storms can leave a damp patch in flooring or skirting long before anyone books a repair. A proactive annual check catches marginal seals and thresholds before they fail outright, which is both cheaper and avoids any secondary damage to the property.
This is particularly relevant for period or listed coastal properties where internal repair work following a water ingress event can be considerably more disruptive and costly than the doorset maintenance that would have prevented it in the first place.
What we bring to a weatherproofing callout
A typical van stock for a weatherproofing visit includes common seal profiles for the major composite door manufacturers, threshold gasket inserts, silicone and hybrid polymer sealants suited to coastal exposure, and the tools needed to adjust multi-point mechanisms and hinges. This means the majority of weatherproofing faults can be diagnosed and resolved in a single visit without a return trip to source parts.
Where a proprietary or unusual seal profile is involved, we'll identify it on the first visit and order the correct part rather than fit an approximate match that won't compress properly - a slightly wrong profile is often worse than leaving the old, worn seal in place until the right one arrives.
Weatherproofing checks alongside a wider door service
Weatherproofing is rarely worth doing entirely in isolation from the rest of the doorset - a hinge that's dropped slightly affects compression just as much as a worn seal does, and a mechanism that's stiff to operate often points to the same debris and grit ingress that's degrading seals and drainage. Booking a weatherproofing check alongside a general hardware service means one visit covers both.
For most Cornwall properties we'd recommend combining an annual weatherproofing check with a lubrication and adjustment pass on hinges and the multi-point mechanism, since both jobs use the same access and the same tools, and catching a hinge issue early prevents it from undoing a fresh seal replacement within a year.
Signs it's time to book a check
A cold line felt around the frame, water at the base of the door after heavy rain, a whistling draught in windy weather, or a damp patch appearing on plaster near the frame are all reasonable triggers to book a weatherproofing check rather than waiting for the problem to worsen. None of these need to have become severe before it's worth calling - catching a marginal seal or a part-blocked drain early keeps the job small.
If in doubt, a diagnostic callout is a low-cost way to get a clear answer on what, if anything, actually needs doing.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Full weatherproofing inspection and service | £120-£180 | Seal, threshold, drainage, compression, letterplate checked |
| Seal or threshold replacement if required | £85-£160 | On top of inspection if a component has failed |
| Sealant joint renewal (frame to wall) | £75-£140 | Depends on perimeter length and access |
| Head drip cill repair or fitting | £90-£160 | Where missing or damaged above the frame |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- Annual weatherproofing service is worth having done professionally.
Prevention
- Do the 6-point check every autumn.
