How a tiled roof keeps water out
Each tile overlaps the one below and locks into its neighbours, so rain runs from tile to tile down into the gutter. It all relies on gravity, which is why pitch matters. Monier says most of its concrete tiles can go as low as 15 degrees, depending on rafter length, wind and the tile's profile.
Under the tiles, many roofs have sarking: a foil or membrane layer that catches wind-driven rain and dust that gets past the tiles and carries it to the gutter. The NCC requires it on every tiled roof pitched below 18 degrees, and on steeper roofs once the rafters pass set lengths. Plenty of older roofs were built without any.
Along the top, ridge and hip caps cover the gaps where slopes meet. On most older roofs they sit on a bed of mortar (the bedding), sealed with a finishing layer called pointing.
Where tiled roofs actually leak
Ridge and hip capping. Monier lists cracked or broken bedding under the caps as a common cause of leaks. Weather cracks the pointing, caps loosen, and rain runs in underneath. Rebedding and repointing with a flexible compound is the fix, and our ridge capping page covers the job.
Cracked and slipped tiles. Mostly from feet, falling branches and hail. If there's sarking underneath, a cracked tile may not drip for a while, which is why the stain often appears long after the damage. Our guide to cracked tiles helps you decide what to do about them.
Valleys. Where two slopes meet in an inside corner, a metal channel carries water from both. Leaves dam it, old metal rusts, and mortar along the edges cracks. See valley leaks.
Flashing. Around chimneys, walls, skylights and vents, older lead or galvanised flashing can lift, split or rust away from the tiles.
The bottom edge. Where there's a gutter, the NCC requires tiles to overhang the fascia or tiling batten by at least 35 mm so water drops into it. Tiles that stop short, or a gutter that overflows, send water behind the fascia and into the eaves.
Tired sarking. Sarking that's torn, sagging or missing in patches lets water that slips past a tile reach the ceiling instead of the gutter.
Terracotta or concrete: does it change anything?
| Terracotta | Concrete | |
|---|---|---|
| Colour | Fired into the clay, and Monier says it won't fade | A surface coat that Monier says fades and weathers with no effect on waterproofing |
| Moss and lichen | Grows more readily, especially on unglazed tiles, though Monier says it stays on the surface | Grows less often than on terracotta |
| Painting | Monier doesn't recommend it, and once painted it needs recoating from then on | Repainting refreshes the look but Monier says it doesn't improve waterproofing |
| Broken tiles | Replaced one at a time | Replaced one at a time |
Things that look like trouble but aren't
A whitish film on concrete tiles is efflorescence, sometimes called bloom. Monier says it's natural salts rising to the surface, it doesn't affect performance, and it usually disappears on its own.
Faded concrete tiles aren't leaking tiles. The colour coat plays no part in keeping water out, so a dull roof can be perfectly watertight.
Moss looks bad, but Monier says it doesn't affect a tile's strength. It's still worth having it cleared where it's building up in valleys or gutters, because moss holds water and slows drainage.
Stay off the tiles
Tiles crack under a boot, especially away from where they overlap, and wet or mossy tiles are slippery. Look from the ground or an upstairs window instead. Some old roofs that look tiled are really asbestos cement slates or shingles, which ASSEA says were made in Australia from the late 1800s to the 1980s. If your roof is from before 1990 and you're not sure what it's made of, don't let anyone pressure clean, drill or cut it until it's been checked.
How to narrow down a tile roof leak from the ground
Run your eye along the ridge
With binoculars, look for caps sitting out of line, gaps in the pointing, or crumbs of mortar collecting in the gutter below.
Scan the slopes row by row
A tile sitting higher than its row, a lighter chip on an edge, or a tile turned slightly askew is worth pointing out to the roofer.
Check the valleys and gutters
Leaves, moss or tile pieces lying in them, or water spilling over in rain, all point to drainage.
Match it to the stain
Under the ridge line usually means capping. Near an inside corner means the valley. Along an outside wall points to the bottom edge or the gutter.
What you can do, and what needs a roofer
You can
- A binocular check of the ridge, valleys and slopes
- Booking gutter and valley cleans: Monier suggests at least once a year, twice under trees
- Trimming branches that brush the roof, where you can reach from the ground
- Keeping trades off the tiles unless they really need to be up there
Leave to a roofer
- Rebedding and repointing ridge capping
- Swapping cracked or slipped tiles
- Clearing or replacing valleys
- Checking the sarking from the roof space
- Moss removal without a pressure washer
Our take on tiled roofs
If the tiles are mostly sound, a leaking tile roof is usually a repair, not a new roof. We'd have the ridge, valleys and any cracked tiles checked in one visit, because on an older roof they tend to fail together. We'd skip a respray as a leak fix. And if the roofer says the whole ridge needs rebedding, we'd compare that price with a tile restoration, which normally includes it.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.