How to Calculate Roof Tiles
Estimating roof tiles accurately is critical to avoid expensive delivery charges for a single missing pack or having a pallet of heavy tiles left over. Calculations vary significantly between tile types due to different overlap requirements.
1. Understanding Headlap
The headlap is the distance the tile above overlaps the tile below it. This is essential for waterproofing. Standard headlaps are 75mm for interlocking tiles and clay plain tiles, while slates often require 100mm in exposed/rainy areas.
2. Calculating the Gauge
The "gauge" is the exposed part of the tile you see once it's on the roof. It is calculated by: (Tile Length - Headlap). For double-lapped tiles like Plain Tiles, the gauge is (Tile Length - Headlap) / 2.
3. Drainage and Angle
Low pitch roofs (below 22.5°) often require a larger headlap to prevent wind-driven rain from being pushed up under the tiles. Always check the manufacturer's specification for the minimum pitch required for your chosen tile.
Expert Tip: Batten Selection
In the UK, the most common roofing batten size is 38x25mm or 50x25mm. Battens should always be "Blue" (graded to BS 5534) to ensure they are strong enough to support the weight of the tiles and the roofer.