How many slates do I need per m2?

For standard 500mm x 250mm slates with a 100mm lap, you will need approximately 20 slates per m². If using smaller 400mm x 250mm slates, the requirement increases to approximately 26.7 slates per m².

What is the correct headlap for slates in the UK?

The headlap is determined by the roof pitch and the level of exposure to wind and rain. For pitches above 30 degrees, a 100mm lap is standard. In sheltered areas with high pitches, this can be reduced to 75mm, while exposed coastal sites often require 125mm.

How do I calculate the batten gauge for slates?

The batten gauge is calculated by subtracting the lap from the total length of the slate and then dividing by two. For a 500mm slate with a 100mm lap: (500 - 100) / 2 = 200mm gauge.

Why are copper nails used for slating?

Copper nails are used because they are highly resistant to corrosion and will typically last as long as the natural slate itself (75-100 years). Galvanised nails will eventually rust and fail, leading to 'nail sickness' where slates slip off the roof.

How many slates do I need per m2?

For standard 500mm x 250mm slates with a 100mm lap, you will need approximately 20 slates per m². If using smaller 400mm x 250mm slates, the requirement increases to approximately 26.7 slates per m².

What is the correct headlap for slates in the UK?

The headlap is determined by the roof pitch and the level of exposure to wind and rain. For pitches above 30 degrees, a 100mm lap is standard. In sheltered areas with high pitches, this can be reduced to 75mm, while exposed coastal sites often require 125mm.

How do I calculate the batten gauge for slates?

The batten gauge is calculated by subtracting the lap from the total length of the slate and then dividing by two. For a 500mm slate with a 100mm lap: (500 - 100) / 2 = 200mm gauge.

Why are copper nails used for slating?

Copper nails are used because they are highly resistant to corrosion and will typically last as long as the natural slate itself (75-100 years). Galvanised nails will eventually rust and fail, leading to 'nail sickness' where slates slip off the roof.

Roof Slate Calculator

Precise material takeoff for slate pitched roofs.

Total Roof Area (m²)

Slate Size (mm)

Required Lap (mm)

Slate Takeoff

Pitch & Lap: In the UK, as the roof pitch decreases, the 'lap' must increase. A 100mm lap is standard for pitches over 30°. For exposed coastal areas, a 125mm lap is safer.

The Timeless Beauty of Natural Slate

Natural vs Synthetic

Slating is one of the most durable and aesthetically pleasing roofing methods in the UK. While natural slates like Welsh Blue or Spanish Grey are the gold standard, modern synthetic slates offer a lighter, more cost-effective alternative with a similar look.

Our **roof slate calculator** provides accurate estimates for both natural and synthetic options, factoring in the critical 'headlap' required for your specific project.

Coverage Guide

500x250mm (Standard)~20 per m²

400x250mm (Small)~27 per m²

600x300mm (Large)~13 per m²

Sorting & Holing

Natural slate is a raw material and varies in thickness. For a professional finish, slates must be 'sorted' into three groups: thick, medium, and thin.

The thickest slates are installed at the bottom of the roof (the eaves), and the thinnest at the top (the ridge). This ensures a level finish across the roof and prevents the slates from 'kicking' or sitting unevenly.

The Headlap Rule

Headlap is the distance by which a slate overlaps the slate two courses below it. This is the primary waterproofing mechanism of a slate roof. If the lap is too small, capillary action can draw water up and over the top of the slate into the roof structure.

Wind Loading

Slates must be twice-nailed to the battens. In very exposed areas (Zone 3 or 4 in the UK wind map), you should also use 'slate hooks' to provide extra mechanical fixing and prevent slates from rattling or lifting in high winds.

Pro Tip: Copper Nails

Never use standard steel nails for natural slate. The slate will outlast the nails by 50 years. Always use 30mm or 35mm **clout copper nails**. They are soft enough to avoid cracking the slate during hammering but strong enough to last a century.

Slating & Roofing FAQ

Technical Disclaimer

Material estimates are based on standard coverage. Natural slate has a higher breakage rate than concrete tiles (allow ~10%). Complex roofs with valleys and hips will require 'slate-and-a-half' widths to ensure correct bonding at the junctions.