Leaking polycarbonate conservatory roof

1Glazing bars and the seals beneath them

Polycarbonate sheets sit between aluminium or uPVC glazing bars, the long rails laid down each slope, ridge to eaves. Each sheet is gripped by a rubber or foam gasket, and a cap clips or screws over the top to hold it all down. In sun and frost the gasket slowly hardens, shrinks and pulls back from the sheet, which leaves a thin channel for water to run along.

The cap matters as much as the seal. Caps that have lifted, cracked in the heat or lost a screw let driving rain straight into the joint. Water then follows the bar down inside the frame and appears at the eaves or on a cill, often a metre or more from the real gap.

Fresh silicone smeared along a bar looks like a repair, but it usually seals the outside of a joint that is failing inside. It can also hide the gap from the next person who looks.

2Ridge, hips and the line against the house wall

The ridge, where the two slopes meet at the top, is closed with a cap and foam or rubber end pieces. On older roofs those pieces shrink and let rain blow in, particularly in a gale off the sea. A lean-to roof has no ridge, but it has the wall edge instead.

That edge is called the abutment: the line where the roof stops against the house wall. Weatherproofing there is a flashing: lead or aluminium strip pushed into a groove in the brickwork and folded down across the roof. Where the flashing has lifted, or was only ever sealed with mastic, water runs behind it and drips off the underside of the frame.

We look at this joint closely, because a damp patch inside the room below the ceiling line, or on the brickwork just above the glazing, is often the abutment and not the roof panels at all.

3Cracked sheets and tired fixings

A sheet that has cracked is easy to spot from a ladder, but hairline splits at a screw hole or along a flute can be hard to see from the ground. Polycarbonate becomes brittle with age, and a hailstone, a fallen branch or a careless foot during cleaning can start a crack that opens over the next winter.

Water can also get inside the sheet. A multiwall sheet is made of long hollow channels, and if the open ends are not sealed with tape or an end cap, rain and dust creep in and the sheet clouds or grows green. That is a different problem from a leak, and it is covered in our page on condensation under a conservatory roof.

One cracked sheet can be swapped. Many cracked sheets on one roof tell a different story: the plastic is reaching the end of its working life.

On a survey we press along each bar and look at the screw heads for stains, because a rusty streak below a fixing shows where water has been getting in for some time.

4Gutters and the eaves beam

A conservatory gutter is small and carries a lot of water for its size, because the whole roof drains into it. Leaves, moss and a sagging bracket make it overflow, and the overflow runs down the face of the frame. It can look exactly like a roof leak from inside.

The eaves beam, the horizontal frame member the roof sits on, is the other usual meeting point for these faults. Water that has entered further up often runs down the bars and gathers there, then drips from the joints of the beam over the windows. Following the wet marks upwards from that point is how we find where it entered.

If the gutter itself has split joints or has fallen out of line, that is a quick repair, and worth doing before anybody replaces a roof.

Clearing the gutter, resetting its fall to the outlet and renewing a perished joint seal are all small jobs. They are worth ruling out first, because they cost far less than a roof.

5Repair the joints, or replace the roof

When the sheets are sound and the fault is a set of tired seals, new gaskets, caps and a reworked flashing will often stop the leak. When the sheets are cracked, cloudy and brittle, and the bars are worn, a new roof is the better use of money.

Published cost guides put a polycarbonate roof's typical life at around 10 to 15 years (HomeBuilding, 2024; The Eco Experts, 2024). MyBuilder (updated 21 August 2026) gives a typical UK range of £2,000 to £5,000 for a polycarbonate replacement and £5,000 to £10,000 for a solid roof. Only a survey shows what your own frame needs, and a written quote follows it.

Before choosing, read how long a conservatory roof lasts and the structural check a heavier roof needs. A solid roof also brings building control into the picture, so allow time for that. The wider conservatory roof replacement service explains the options.