The short answer
Resealing works when water is getting in at a sound, dry joint, such as a glazing bar cap or the edge of a sheet where old sealant has shrunk. It does not cure perished gaskets, warped bars, cracked panels or failed flashings. A survey finds which one you have, because sealant over the wrong fault only moves the leak somewhere else.
Where sealant belongs on a conservatory roof
Sealant is a maintenance material, not a structural one. It is useful in a few specific places: around a clean junction where two sound surfaces meet, at the small cap or end piece of a glazing bar, and as a finishing bead on the edge of a sheet or panel where a previous bead has shrunk or split.
In those spots it does the job quickly and cheaply, and a careful reseal can add a few more seasons to a roof that is otherwise in good order. The surfaces need to be clean, dry and sound, and the old sealant has to be cut out first. New sealant laid over old, dirty or damp material does not bond, and it lets go within a winter.
Most conservatory roofs rely on rubber or EPDM gaskets to seal sheets and glass into aluminium or uPVC bars, with sealant as a back-up rather than the main barrier. That is why the first question on a survey is what is actually holding the water out.
Faults that sealant will not fix
Several common leaks look like a sealant problem from below and are not.
- Perished gaskets. Rubber hardens and shrinks with age and sunlight. Once a gasket has pulled away from the glass, a bead of sealant on top is a short-term patch at best.
- Cracked or crazed sheets. A split polycarbonate sheet or a chipped glass unit has to be replaced. Our page on replacing a polycarbonate sheet covers when a single panel is enough.
- Failed flashing. At the wall junction, a lead flashing or a mortar fillet can lift, crack or pull out of the brickwork. Sealant over that joint hides the movement without stopping it.
- Blocked or sagging gutters. Overflow at the eaves is easily mistaken for a roof leak.
- A moving frame. If the bars have bowed or the frame has shifted, the joints open repeatedly and every reseal splits again.
A roof with several of these at once is usually worn out, and the budget goes further on a new roof than on repeated patching.
How to tell what is leaking
Water is a poor witness. It runs along a bar or a sheet edge and drips from somewhere that may be a metre away from where it came in. Dripping at a corner might mean a failed flashing, a blocked gutter or a gasket gap at the other end of the bar.
A few checks help before anyone climbs a ladder. Look at the roof after heavy rain and note where it drips and when it stops. Check the inside face of the glazing bars for staining or green algae. Look for condensation as well, since a roof that runs with moisture on a cold morning can feel like a leak when it is not. Our guide to conservatory roof leaks goes into this in more detail, and the page on conservatory roof condensation helps you tell the two apart.
Please do not walk on a conservatory roof. Polycarbonate and old glass are not designed to take a person's weight, and the fall can be serious.
What a repair costs compared with a new roof
A resealing visit is normally treated as a minor repair. MyBuilder's roof repair guide, updated in August 2026, gives minor repairs as roughly £100 to £300 across the UK, with moderate repairs at £500 to £1,000. Those are national guide figures rather than anything we charge, and access, roof size and the state of the joints all move the number.
For comparison, MyBuilder's conservatory roof guide gives an average replacement of around £4,500, with a range of £2,000 to £10,000 or more, and polycarbonate at £2,000 to £5,000. If a roof needs repeated repairs in successive winters, the comparison is worth making. A repair that does not last is poor value, however small the bill looks on the day.
Polycarbonate roofs are quoted at around 10 to 15 years of typical life, so the age of your roof is one more factor in the decision.
Sealant, silicone and the wrong product
Not all sealants are equal. A bathroom silicone bought for a quick fix tends to peel in sunlight and is almost impossible to remove cleanly later. Roof joints need a sealant that suits the surface and the movement of the roof, which expands and contracts through each day and each season.
That movement is the real enemy. Aluminium, uPVC and polycarbonate each expand by a different amount, so a rigid bead cracks at the interface. Properly designed roofs allow for movement in the gaskets and the way the bars are fixed. Sealant that spans a moving gap will usually fail where the gap is widest. We reseal only where the joints are sound and the movement is small, and when the real answer is a gasket or a new sheet, that is what we tell you.
What happens at a survey
A survey starts with the view from inside and outside. We check gaskets, caps, flashings and gutters, and photograph each fault. The quote arrives in writing and names the remedy, which might be a reseal, a gasket change or a new roof. Where a modest repair will hold, a modest repair is what the quote offers.
If you want to see the wider choices, the conservatory roof replacement page sets them out, and checking a conservatory frame covers the structure underneath. Our workmanship guarantee lasts 10 years and is written down, and we take away what we strip off.