Head Laps

Use these charts to assist with selecting the correct Head Laps for you.

The tables below show Minimum Recommended Head Laps

Moderate Exposure (less than 56.6 l/m2 per spell)

Size - Nominal (mm)	20˚	22.5˚	25˚	27.5˚	30˚	35˚	40˚	45˚ to 75˚	85˚
600 x 300	-	-	95	85	80	70	60	55	-
500 x 300	115	105	95	85	80	70	60	55	-
500 x 250	-	-	95	85	80	70	60	55	50
460 x 225	-	-	-	-	80	70	60	55	50
400 x 250	-	-	-	-	80	70	60	55	50
400 x 200	-	-	-	-	80	70	60	55	50
350 x 250	-	-	-	-	80	70	60	55	50
350 x 200	-	-	-	-	80	70	60	55	50
300 x 200	-	-	-	-	80	70	60	55	50

Values calculated using nominal sizes and incorporating a 5mm joint gap as per BS8000: part 6: 1990. We recommended the addition of at least 5% wastage allowance.

Severe Exposure (56.6 l/m2 or greater per spell)

Size - Nominal (mm)	20˚	22.5˚	25˚	27.5˚	30˚	35˚	40˚	45˚ to 75˚	85˚
600 x 300	-	-	-	-	100	90	80	70	-
500 x 300	-	130	120	110	100	90	80	70	-
500 x 250	-	-	-	110	100	90	80	70	65
460 x 225	-	-	-	-	100	90	80	70	65
400 x 250	-	-	-	-	100	90	80	70	65
400 x 200	-	-	-	-	100	90	80	70	65
350 x 250	-	-	-	-	100	90	80	70	65
350 x 200	-	-	-	-	100	90	80	70	65
300 x 200	-	-	-	-	100	90	80	70	65

(Based on BS5534: 2003 – All headlaps have been rounded up to the nearest 5mm)

Wind Loads & Weather Resistance

Slates correctly fixed will have adequate resistance to wind loads, wind uplift and rain penetration under most conditions. The tables above give minimum recommended laps according to exposure, roof pitch and slate size.

Detailed guidance on wind load calculations is given in BS5534: 2003 and BS6399, Part 2: 1997 and Part 3: 1998.