Seal a leaking conservatory roof

Find the leaking joint, clear old sealant, then reseal the roof and house-wall flashing properly so it stays watertight.

CR-01Confirm it's a leak, not condensationCheck the damp patch during or just after heavy rain, not simply when the ceiling looks marked. Condensation shows as a general film across the glazing, while a leak leaves a clear wet trail running from one specific point. Look inside for staining below a particular glazing bar, the ridge, or the join with the house wall.

1 each · Torch

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CR-02Pick a dry day and gather your kitWait for a still, dry day with no rain forecast for at least 24 hours, so the new sealant can bond and cure properly. Set your ladder up on firm, level ground and use the safe working-at-height habits you already know. Get everything ready before you climb up: sealant gun, scraper, cleaning solvent, cloths and the right sealant for your roof material.

1 each · Sealant gun

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1 tube · Roof & gutter sealant

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1 bottle (500ml) · Methylated spirit

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1 pack · Cleaning cloths

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CR-03Inspect every joint and mark the failuresWork along the ridge, each glazing bar end, the eaves, and the strip where the roof meets the house wall — these are the usual weak points. Look for sealant that's cracked, shrunk or missing, and rubber gaskets that have gone hard or pulled loose. Stick a bit of masking tape by each fault so you don't lose track once you're back on the ground.

1 roll · Masking tape

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CR-04Clear the guttering before you reseal anythingA blocked gutter overflows and can look exactly like a roof leak, so rule this out first. Clear leaves and debris by hand or with a gutter scoop, then flush through with a hose and check water runs freely out of the downpipe at the bottom. This can save you resealing a joint that was never actually the problem.

1 each · Gutter scoop

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1 pack · Disposable gloves

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CR-05Rake out the old, failed sealantPull out all the old sealant from each marked joint with a scraper or sealant-removal tool — new sealant won't grip properly if it's applied over old, perished sealant. Wipe the joint clean with a cloth and methylated spirit and let it dry fully. Wear gloves, as old sealant dust and offcuts can irritate skin.

1 each · Sealant removal scraper

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1 bottle (500ml) · Methylated spirit

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CR-06Replace any perished rubber gasketsWhere a glazing bar uses a rubber seal rather than sealant, pull out any gasket that's gone hard, cracked or shrunk. Cut a new matching gasket to length with a sharp blade and press it fully into its groove along the whole run. A missing or mismatched gasket is a common reason a leak keeps coming back after resealing.

1 5m roll · Replacement glazing bar gasket

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1 each · Craft knife blade

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CR-07Re-fix a loose flashing strip, if there is oneIf the flashing where the roof meets the house wall has pulled away, fix it back in place before resealing — sealant alone won't hold a loose strip. This wall is almost always solid brick or block behind render or facing brick, so drill a 6mm hole to about 40mm deep and fit a wall plug with a 40-50mm masonry screw. Before you drill, find your stopcock (usually under the kitchen sink) and check it turns, and check the area with a cable and pipe detector — then still treat it as if something could be there anyway, since detectors miss deep or shielded cables and pipes; if in doubt, isolate the circuit at the consumer unit first. If the wall is a timber-framed extension rather than solid masonry, screw straight into the timber frame behind the cladding instead of using a plug.

1 each · Masonry drill bit, 6mm

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1 pack of 10 · Wall plugs

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1 pack of 10 · Masonry screws, 40-50mm

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1 each · Cable and pipe detector

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CR-08Apply the new sealantMask both sides of each joint with tape to keep the line neat, then run a continuous bead of sealant using your usual technique — no gaps, no thin patches. Tool the bead smooth with a wet finger or a smoothing tool, then peel the tape away while the sealant is still wet. Work through every joint you marked, including the flashing once it's re-fixed.

1 tube · Roof & gutter sealant

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1 each · Sealant smoothing tool

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CR-09Let it cure, then test with a hoseCheck the tube for cure time — most roof sealants need at least 24 hours dry, longer in cold weather. Once cured, test from ground level with a hose on a gentle setting, running water over each repaired joint for a few minutes while someone checks inside for drips. Only get onto the roof itself if it's built to be walked on — most polycarbonate and glass conservatory roofs are not.

1 each · Garden hose

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CR-10Tidy upWipe tools clean with meths before leftover sealant sets hard on them, and reseal or bin the sealant tube. Bag up old gasket offcuts, scraped-out sealant and used masking tape for general waste. Store any spare sealant somewhere frost-free, as most types don't survive freezing.

1 roll · Bin bags

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KNOW THE RULES

Before you start: Do I need planning permission for a single-storey rear extension?

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