Few roofs have as many joints for their size as a conservatory roof, and every joint depends on a seal that flexes with the sun and the frost. Glass and polycarbonate do not wear out the way a tile does, but the rubbers, silicone and sealing strips around them do. When one lets go, water finds a route through the frame and arrives as a drip on the floor, a damp patch on the house wall or a wet cill.
The difficulty is that the drip is rarely where the fault is. Water runs along bars, down the inside of the frame and across the eaves beam before it shows itself. This guide takes the usual points in the order we check them, explains what each one looks like and also says whether a small repair is likely to last or only postpone the problem. Weighing a repair against a new roof? Our conservatory roof replacement page explains how we decide.
Tracing the real point of entry
Before anyone reaches for a tube of sealant, take ten minutes to watch the leak. The pattern tells you a great deal.
A drip that appears only in heavy rain points to a gap that needs plenty of water to fill. A drip that appears after any rain, however light, suggests a sizeable failure such as a lifted bar cap, a cracked sheet or a blocked gutter. A leak that keeps going after the rain stops usually means water is stored somewhere, running slowly along a bar or sitting in a cavity, and draining out late.
Does the position of the drip help?
It helps, but it can mislead. Drips along the ridge suggest a failed ridge seal or cap. Drips at the glazing bars along the length of the roof point to the bar seals. Wet patches on the house wall above the roof point to the flashing. Water pooling along the eaves points to the gutter or the eaves beam. Where water appears at one corner, it has often run there along a slope, so look higher than you think.
Is it a leak or condensation?
A conservatory is a damp room by nature. If droplets form on the inside of the glass overnight and the leak is worst on cold, still mornings with no rain, you are dealing with condensation, not a failed seal. Our condensation guide covers that case separately.
Failed seals and perished gaskets
Most glazed conservatory roofs rely on a rubber gasket or a bead of silicone between each pane and its glazing bar. Both are exposed to sunlight and to a cycle of heating and cooling that stretches and squeezes them every day. Over the years they harden, shrink, crack and pull away from the glass, leaving a thin gap along the length of a bar.
A perished gasket is easy to spot once you know what to look for. The rubber looks dry, flaky or dented, or it has shrunk back at the corners so you can see a gap. Black mould along the line of a seal is also a sign that water is sitting in the joint.
Replacing a gasket is a proper repair and the best fix where the glass and bars are otherwise sound. Pushing silicone over the top of a worn gasket is not. It covers the gap for a season, then peels as the materials move at different rates, and it makes the later job harder because the old silicone has to be cleaned out first.
If the seals are failing all over the roof, not in one place, that usually means the whole roof is wearing out together, and replacing the covering becomes the more sensible spend.
Glazing bars, end caps and cracked sheets
Glazing bars are the aluminium or uPVC sections that carry each pane. Water can enter a bar in several ways: through a missing cap at the end of the bar, through a split at a joint, or through a corroded section that has let moisture into the core. On older roofs the bar cappings that hold the glass down may have loosened, letting rain run under them.
What goes wrong with polycarbonate sheets?
Polycarbonate roofs have their own faults. Sheets expand and contract, so a sheet that is fixed too tightly can crack at a screw hole or along a bar. The end-sealing tape on the sheets can fail, letting water into the channels inside the sheet, where it shows as green algae or a cloudy patch. A single cracked sheet can come out and be swapped for a new one on its own, which is why replacing one polycarbonate sheet is often worth considering before a new roof.
Can cracked glass leak?
A cracked outer pane of a double-glazed unit can leak, and if the inner seal has also failed the unit mists up. A unit like that cannot be dried out and needs replacing. Self-cleaning glass is sometimes damaged by harsh cleaning, so see our page on self-cleaning glass for what is safe to use.
The flashing along the house wall
Where the conservatory roof runs into the wall of the house, a flashing seals the gap. On many conservatories this is a strip of lead, set into a slot cut across the brickwork or a mortar joint and dressed down over the top of the roof. Some use a flexible rubber or a sealed aluminium strip instead.
This is a classic leak point, because the house and the conservatory move at different rates and are fixed to different foundations. Over time the sealing mortar around the lead cracks and lets the metal pull away. Lead itself can split at a bend formed too sharply. If the flashing is only held with sealant, the sealant will have failed long before the metal has.
According to Leadworx, Code 4 lead has become the usual pick for general flashing, and a strip that is too thin or cut too long is likelier to crack. We look at how it has been fitted, how far it is tucked into the wall, whether it was ever fully lapped over the roof and whether the pointing above it is sound.
Wet patches on the wall inside the house, directly above the conservatory, are rarely a problem with the house roof. They are far more often the flashing.
Repairing a flashing means raking out the old joint, refitting or replacing the lead and repointing. Where the junction is easy to reach the work is modest; behind a gutter or fascia it takes longer.
Gutters, eaves and the ridge
A conservatory gutter handles all the water that comes off a large glass roof, usually through a single downpipe. If it blocks, it overflows, and the water can run back behind the gutter and into the frame at the eaves. If it has dropped at a bracket, it holds water and spills at the wrong place.
Gutter makers advise a slight slope toward the outlet, in the region of 1:600 to 1:350 depending on the system, and the brackets should sit close together. A gutter that sags between brackets will pond. Leaves, moss and sediment rinsed from the roof are the usual blockages, and a conservatory under a tree may need clearing several times a year.
How does the ridge leak?
The ridge is the highest line, where two slopes join or a lean-to slope reaches the house wall. Ridge seals and end caps face the full weight of rain and sun. A failed ridge seal usually drips at the highest point and is easy to confuse with a flashing fault. Our conservatory gutters page goes into the drainage side in more detail.
A frame that has moved can cause a whole set of apparent leaks at once. Our frame checks page explains what we look for when the same fault keeps coming back.
Leaks in solid and lightweight tiled conservatory roofs
A solid or tiled roof leaks in the same way any pitched roof does: at the junctions. The flashing at the house wall, the valleys where two roof sections meet, the ridge and the hips are all places where water can get under the covering. Tiled roofs add the possibility of a slipped or cracked tile, though a modern tiled roof with a sound underlay behind the tiles usually survives that.
Many lightweight tiled systems use large panels carrying a tile or slate surface over an insulated core. The joints between panels are sealed and the fixings pass through the surface, so a missing cap or a loosened fixing can let water into the core. Our guide to lightweight tiled roofs explains how they are built and what to check.
Leaks under a solid roof can be harder to trace, since water may travel along the underlay or the insulation before it shows up on the new ceiling. Stains that appear weeks after a storm are a sign that water is moving slowly through the build-up. Do not leave them, because the timber and plasterboard inside deteriorate quietly.
If you have recently had a solid roof fitted and it leaks, the installer's workmanship guarantee should be the first call. Ask for the paperwork before you pay anyone else to look at it.
Repair, seal or replace
Sealant is the tool most people reach for, and it has a legitimate place. A bead applied to a clean, dry joint in dry weather can slow a leak during a storm or buy time until a proper repair. It should be treated as temporary. Applied over wet or dirty surfaces it does not bond, and applied over a moving joint it tears.
The proper repair depends on the fault: new gaskets, new bar caps, a replacement sheet, a new flashing, a cleared and re-fixed gutter. Every one of those costs less than a new roof, and where it genuinely cures the fault we will recommend just that. Where the seals have failed across the whole roof, the frame has moved or the covering is past its best, repairing one point after another costs more over time than replacing it.
The survey makes the decision plain. We photograph what we find on your own roof, mark the fault points and send a written quote, which lets you weigh repair against replacement using what the photographs show. Our insulation guide explains why adding a liner is not a leak fix. Our own work is covered by a written guarantee on workmanship, running for ten years, and we leave the property tidy with the waste removed.
Call 01793 626096 or send photographs by WhatsApp, or use the enquiry form, and tell us what you can see from the garden.