The interlock of a roof tile is the system by which tiles grip into each other, preventing wind and rain from getting under the tiles. Every roof tile has special edges, grooves or nibs along the sides and at the top and bottom that engage with the adjacent tile. This interlocking system determines the weathertightness of the roof.
Types of interlocks
| Interlock | How it works | Example |
|---|---|---|
| **Single interlock** | Simple overlap at the side | Traditional pan tile |
| **Double interlock** | Double groove at the side | Many modern interlocking tiles |
| **Triple interlock** | Groove at side, head and tail | High-performance stormproof tiles |
| **Head lock** | Extra groove at the top where tiles overlap | Prevents lifting by wind |
Why is the interlock important?
- Weathertightness — a good interlock prevents rainwater (including wind-driven rain) from getting under the tiles
- Storm resistance — the more interlocks, the better the tile stays in place during high winds
- Roof ventilation — the interlock must seal sufficiently, yet also allow air through for ventilation beneath the tiles
Interlock and roof pitch
The minimum roof pitch depends on the type of interlock:
| Interlock | Minimum roof pitch |
|---|---|
| Single interlock | Approx. 35 degrees |
| Double interlock | Approx. 25-30 degrees |
| Triple interlock | Approx. 15-25 degrees |
At a low roof pitch, a tile with multiple interlocks is necessary to remain weathertight.
Inspection and maintenance
- Check annually that tiles are still properly engaged in their interlocks
- Reposition displaced tiles, replace broken tiles
- Watch for moss and debris in the interlock grooves — this can disrupt the seal
Related terms
- Roof tile
- Roof pitch
- Roof boarding
- Ridge tile
- Tile batten