Where is my roof leaking from?

The short answer

Water gets into a pitched roof at a junction far more often than through the middle of a slope: a chimney flashing, a valley, a ridge, a wall abutment, or the eaves.

Once in, it runs downhill along the felt or a rafter until it meets a nail, a joint or a low point, then drops. The stain marks where it dropped, not where it came in.

Start upstairs with the weather pattern, go into the loft with a torch during rain if you can, then look at the roof from the ground above and uphill of the wet spot.

Step one: what does the leak do

Before going anywhere near the loft, think about when it happens. A leak that appears with every shower is an open hole: a missing slate, a cracked tile, a split valley. A leak that only appears in wind from one direction is a flashing or a ridge, where rain has to be driven under something to get in. A leak that shows up after a long dry spell followed by heavy rain is often a blocked gutter or valley overflowing back under the slates. A leak that gets worse in cold weather and dries up in summer might not be a leak at all; it can be condensation in an unventilated roof space dripping off the felt.

Note which room, which wall, whether the stain is near an outside wall, a chimney breast or the middle of the ceiling, and whether it is growing. That is half the tracing done.

Step two: the loft

Go up with a good torch, ideally while it is raining. Look above and uphill of the stain, remembering that the water has run down to get there. What you are looking for is a dark streak on the underside of the felt, a wet or stained rafter, a run of drips off a batten, a wet patch on the insulation, or daylight where there should be none. Follow the wet line upwards until it stops; that is roughly under the entry point.

Check the obvious suspects as you go. The back of the chimney where it comes through the roof. Any valley, which from inside is where two slopes meet in a trough. Any pipe or vent that comes up through the slates. The felt at the eaves, above the wall plate, which rots where it sat in the gutter and lets water run back inside instead of out. And the ridge, along the top, where wind-driven rain gets in under loose ridge tiles.

Do not walk on the ceiling. Stay on the joists or a board laid across them.

Step three: the roof from the ground

Stand back on the road or in the garden where you can see the slope above the wet spot, and look. Binoculars or a phone camera zoomed in help. You are looking for a slate that has slipped down out of line, a gap where one is missing, a tile that is cracked or sitting proud, a ridge tile with a dark gap under it, mortar missing along a verge, moss packed into a valley, or lead flashing at the chimney that has lifted away from the brick or is pulled out of the mortar joint.

If the stain is beside a chimney breast, look at the chimney: cracked flaunching on top, missing pointing, a lifted apron flashing at the front. If it is at an outside wall near the eaves, look at the gutter for overflow marks and the fascia for peeling paint. If it is under a valley, look at the valley for moss and debris.

The usual suspects, in order

From our own calls across Dublin, Wicklow and Kildare, roughly in the order we find them.

• Lead flashing at a chimney or a wall: cracked, lifted, or the mortar it was chased into has fallen out
• A blocked or split valley: moss backs the water up under the slates, or the liner has split along a fold
• A slipped or missing slate, or a cracked tile, on the slope above the stain
• Ridge or hip tiles with the mortar gone, letting driven rain in along the top
• Rotten felt at the eaves, so water off the felt runs back along the batten instead of into the gutter
• A gutter that is blocked or has dropped off its fall, overflowing at the back onto the wall and the soffit
• The seal around a vent pipe, skylight or aerial fixing
• Condensation, not a leak: a cold, unventilated loft with the felt dripping in winter

What not to do

Do not go on the roof. Slates are slippery wet and dry, tiles crack underfoot, and the fall is the part that hurts. Do not fire sealant at anything from a ladder; it does not fix a flashing or a valley, it makes the proper repair harder, and it hides the fault from the next person who looks. And do not assume it is a new roof. Nearly every leak we see is one failed junction, and that is a repair.

What is worth doing: catch the water, move anything under the stain, and take photos of the ceiling and of the roof from the ground. Send us those with a note of when the leak happens and we can often say what it is likely to be before we come out.

How it goes

1. Send the photos and the pattern. The stain, the roof from the ground, and when it happens. That is usually enough for us to say what it probably is.
2. We trace it from the loft and the roof. Same-week visit on most calls, sooner if water is coming in now. We photograph the entry point from the ladder before quoting.
3. Written quote for the actual fault. Within 48 hours, describing what failed and what will replace it. Not a patch, and not a new roof unless the photos show it needs one.
4. Repair, photos, done. Most leak repairs are a half day to a day. Before and after photos from the same spot the same day.

What we do not do

This guide covers pitched slate and tile roofs on houses, which is what we repair. Flat felt roofs leak differently, usually at a lap or where water ponds, and we will tell you on the phone whether yours is one we can take on. If tracing a leak shows the felt and battens have gone across the whole roof, that is a re-roof and we will say so rather than patch it.

Common questions

Why is the wet patch nowhere near where I think the leak is?

Because water runs. It comes in at a flashing or a slipped slate, travels down the felt or along a rafter, and drops where it meets a nail or a joint. The stain can be a couple of metres downhill of the entry point. Trace upwards from the stain, never straight up.

Could it be condensation rather than a leak?

Yes, especially in a cold loft with no ventilation and a lot of insulation. Condensation shows in cold weather regardless of rain, drips off the felt everywhere rather than in one line, and dries up in summer. A leak follows the rain. If you are not sure, a look in the loft during and after rain usually settles it.

Should I wait for dry weather to get it looked at?

No. A leak that only shows in rain is easiest to find in rain. Ring while it is happening, and if we cannot get there that day, photograph the loft while it is wet so we can see the water track.

Does a leak mean I need a new roof?

Almost never on its own. One failed flashing, valley, ridge or slate is a repair. A roof only needs replacing when the covering or the timber has failed across the whole thing, and we will show you the photos and say which yours is.

Get a free quote

Call 085 781 4603 or request a quote. Free site visit, written quote within 48 hours.