Question answered
Conservatory roof bar cappings
The short answer
Bar cappings are the strips that clip or screw over each glazing bar, pinching the glass or sheet against a gasket and shedding water. They fail when the plastic or aluminium cracks, the fixings loosen, the end caps go missing or the gasket beneath hardens. A drip along a bar is the classic sign. Replacing the capping and gasket properly lasts, while a bead of sealant on top rarely does.
The cappings along your conservatory roof bars hold the glazing down and keep the joints dry. When they crack, spring or lose their seal, the drip usually shows up along a bar.
What a capping actually does
Each glazing bar is the rafter of the conservatory roof. The glass or polycarbonate sits on either side of it, bedded on a rubber gasket. The capping goes over the top and is fixed down through the bar, pinning the glazing in place and covering the joint so that rain runs over it, not into it.
It is a small part doing two jobs: holding and sealing. Because it sits on top of the roof it takes the sun, the frost and the gales first, and it is often the earliest thing to fail. The bar underneath, usually aluminium or uPVC, can be perfectly sound while the cap above has let go, which is why a roof with a good frame can still drip steadily in every shower. At the eaves and the ridge, end caps finish the run and keep birds and insects out of the hollow bar.
How cappings fail
Plastic caps become brittle with age and ultraviolet light, then crack along their length or at the screw positions. Aluminium caps stay whole but can lift when their fixings loosen or the thermal movement works them free. Gaskets harden and shrink, leaving a thin channel for water to follow. End caps at the eaves and ridge fall out, which lets rain run straight into the open bar section.
Wind makes every one of these worse. A cap that sits loose in calm weather can lift in a gale and let driven rain under the glazing. Sea weather on this coast tests small parts hard, so a roof that has stood for a decade often shows several failing at once. Screws that have rusted or backed out are common, particularly on roofs that have not been checked for years, and a missing screw is easy to spot from inside as a pinhead of daylight.
Telling a capping leak from condensation
Water on the inside of a conservatory roof is not always a leak. Condensation forms when warm, damp air meets a cold surface, and it can run along a bar and drip in a line that looks just like a capping fault. Condensation tends to appear on cold mornings, in rows across the whole roof, and with no link to rain. It is also heavier in a room with no ventilation, so open a vent and see whether the pattern changes.
A real capping leak appears during or just after rain, at a particular bar, often near a join or an end cap. If the drips follow the weather, suspect the cap or gasket. If they follow the temperature, look at ventilation and glazing instead. Our conservatory structural check guide shows what we look at when the frame is moving as well, because a bar that has shifted opens its joints from underneath.
Repair, replacement or sealant
A tube of sealant along the bar can stop a drip for a season. It also traps water beneath the cap, hides the failure and makes the proper repair harder later. Replacing the cap and gasket on the affected bars treats the cause, and it is usually quicker than owners expect.
The new cap has to match your bar system, so the section shape, the cut length and the screws all matter. Caps from different makers often sit badly together, leaving a gap along one edge that looks tidy from the garden and leaks from inside. Where the glazing is also yellowed or cracked, replacing the caps alone only delays a larger decision, and the roof may be nearer the end of its life than the cappings suggest. We weigh that up at the survey and propose the lightest job that stops the water for good, whether that is a handful of caps or a different roof.
What to expect from a visit
We check the caps, gaskets and fixings bar by bar, tapping each cap to hear a loose one, and photograph the faults so you can see each one for yourself. The quote arrives in writing afterwards as one total, and it reflects the roof height, the number of bars affected and the access. The conservatory roof replacement page shows the wider choices if the roof is tired.
If you would like to change the look at the same time, the colour of the caps is part of it, and our guide to tile finishes for a solid conservatory roof covers the solid alternative. If a roof window is on your mind, see adding a roof window to a conservatory roof. Coated glass leaves the cappings exactly as they were, so the leak risk stays the same.
Cappings: two things to check
Can I replace a single capping myself?
On a ground-floor lean-to you can sometimes reach it from inside, but the work is on a fragile roof, and the wrong profile or fixings will leak again. If you cannot reach it from a stable platform below the roof line, do not climb onto the sheets. Ask for a survey instead.
Why do water marks appear under the bars after rain?
Water has usually found a way past the capping or the gasket and run down the bar. Look for the highest point where the mark begins, because the entry is above it. That point is where a survey starts, and it is rarely where the stain looks worst.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
10-year workmanship guarantee, in writing.