This one is a good example of why a tile roof can leak even when it looks perfectly fine, not just from the ground but even when you are standing on it. We were on a tile roof in Burnaby chasing a leak, and every tile looked intact. Nothing was broken that you could see. The problem was hidden underneath, in the part of the tile that the next tile covers up. Here is what was going on.
How water moves on a tile roof
Each roof tile has a water channel molded into it, a raised lip and groove along the side that catches water and carries it down to the tile below. The tiles overlap as they run up the roof, so the bottom of one tile sits over the top of the next, and the channels line up to pass water from tile to tile all the way down to the gutter. As long as those channels are intact, the water stays on top of the tiles and never touches the roof underneath.
The hidden break
On this roof, the water channel on the lower part of a tile was broken. The catch is where it was broken. It was up under the spot where the tile above overlaps it, so from the surface you cannot see a thing. The tile above hides it completely. I only found it by lifting the overlapping tile.
With the tile lifted you can see the break clearly. Water coming down the channel hits that break, spills out of the channel, and runs under the tiles instead of over them. From there it soaks into the underlayment and finds its way inside. It does not take a big break either. A small one in the wrong spot is enough.
Why these are the hard ones to find
This is one of the trickiest leaks to track down on a tile roof, because the roof passes every visual check. No slipped tiles, no broken tiles you can see, nothing obvious. But the leak is real. Here is another broken bottom channel on the same style of tile. This one is broken where it still overlaps the tile below it, so it may not be leaking yet, but it is the same failure waiting to happen.
You have to know to look for it, and you have to be willing to lift tiles and check the channels underneath. That is the only way to catch a break that is hiding under the overlap.
What we do about it
When we find a broken channel like this, we replace the affected tile so the channel is whole again and water stays where it belongs, on top of the roof. If we are already up there for a leak we cannot otherwise explain, this is one of the first hidden causes we check for.
If you have a tile roof with a leak you cannot find, do not assume the roof is fine just because the tiles look intact. A broken water channel hiding under the overlap is a common cause, and it takes someone who knows tile to find it. We repair tile roofs across Greater Vancouver and serve Burnaby and the surrounding area. You can also read how a single slid tile flooded a garage in Coquitlam. Call 778-389-5564 for a free estimate.