Patch a leaking felt shed roof by finding the leak, cutting away damaged felt, and sealing a new patch with bitumen adhesive.
SR-01Pick a dry day and gather your kitRoofing repairs need dry, mild weather. Bitumen adhesive won't bond properly below about 5°C, and you can't work on wet felt. Check the forecast for a dry spell of at least 24 hours before and after the job.
SR-02Set up your ladder and get onto the roof safelyMost shed roofs are flat or low-pitch and light-duty — spread your weight with a wide board laid across the roof timbers rather than standing directly on the felt. Wear gloves and check the roof deck feels solid underfoot before putting your full weight on it. If the timber feels soft or springy, get down and check it from inside the shed first.
1 each · Scaffold board or plank (to spread weight)
SR-03Find the leak from outsideLook for split, blistered, or lifted felt, torn edges around vents or the roof edge, and nails that have worked loose. Cracked or perished felt often looks grey and chalky rather than black. Mark any damage with chalk so you can find it again once you're working close up.
SR-04Check the leak from inside the shedGo inside and look at the underside of the roof for damp patches, staining, or drips. This tells you the true position of the leak, which is often not directly below the damage you saw outside — water tracks sideways along the timbers before it drips through. Note the position relative to a rafter or the roof edge so you can find the same spot outside.
SR-05Clear and dry the roof surfaceSweep off leaves, moss, and grit with a stiff brush. The area must be completely dry and clean before you apply any adhesive — bitumen won't stick to a damp or dirty surface. If it's been raining, leave a few hours of dry weather before continuing.
SR-06Cut away the damaged feltUsing a sharp utility knife, cut out the split or blistered section back to sound felt, leaving a neat rectangle or square. Pull out any old, corroded felt nails as you go. If the felt underneath is also perished over a wide area, a patch won't hold long-term and the whole roof covering needs replacing — that's a bigger job than this repair.
SR-07Cut a patch and apply the adhesiveCut a patch of new roofing felt at least 75mm bigger than the hole on every side, so it overlaps sound felt all round. Spread bitumen roofing adhesive evenly over the repair area and the underside edge of the patch using a trowel or a wide filler knife. Work it right up to the edges — gaps are where water gets back in.
1 m2 · Roofing felt offcut (self-adhesive or standard)
SR-08Press the patch down and nail the edgesLay the patch onto the wet adhesive and press it down firmly from the centre outwards to push out any air bubbles. Nail the outer edges every 50mm using galvanised felt nails, driven into the roof timber below, not just into the felt. Take care not to drive nails where you know a rafter isn't underneath — that's a hollow spot and the nail won't hold.
SR-09Seal all edges and any exposed nail headsRun a bead of roofing mastic sealant along every edge of the patch and over every nail head, then smooth it with a wet finger or filler knife. This is what actually keeps water out — bare nail heads and patch edges are the first place a new roof leak starts again. Let it skin over before you leave the roof.
SR-10Check the rest of the roof while you're up thereLook over the whole roof for other lifted edges, loose nails, or worn felt around the perimeter and any roof vent. It's much easier to fix small problems now than to climb up again for a second leak next month.
SR-11Clear up and dispose of the wasteBag up the offcuts of old felt and any bent nails and put them in your general waste bin — small amounts of felt offcuts are fine for a normal household bin, but a full roof strip-off may need a council skip or tip run. Wipe any adhesive off tools with white spirit before it sets hard.
SR-12Test the repairOnce the sealant has cured for a few hours, run a hose gently over the patch and check inside the shed for any sign of water getting through. Check again after the next real rainfall to be sure the fix has held.
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