David Wallace International - Slate UK Crates of Slate

Slate Menu

Annual Rain Index

Map of UK

This map shows the annual driving rain index. Exposure gradings and local knowledge should be referred to when discussing design requirements.

In general, any area within 30 miles of a west facing coast line is considered to be in a severe exposure area. However, localised effects on any site must also be taken into consideration.

Further reference to BS 8104 is advisable to ascertain localised effects.

Map based on BS 5534.

Exposure Zones

Approximate Wind Driven Rain (Litres /m2 per spell)

< less than 56.5l /m2 per spell (moderate)
> greater than 56.5l /m2 per spell (severe)
 

These tables give a range of sizes for your information. Other sizes may be available, please contact us for further information.

(Tables based on BS 5534: 2003 - All headlaps have been rounded up to the nearest 5mm increment)

Wind Loads and Weather Resistance

Slates fixed in accordance with the details given in this guide will have adequate resistance to wind loads, wind uplift and rain penetration under most conditions. The tables give minimum recommended laps according to exposure, roof pitch and slate size.

Detailed guidance on wind load calculations is given in BS 5534: 2003 and BS 6399, Part 2: 1997 and Part 3: 1988.

Minimum Recommended Headlaps

 

 

Moderate Exposure < less than 56.5l /m2 per spell

 Size (Nominal) Min Rafter Pitch
mm 20° 22.5° 25° 27.5° 30° 35° 40° 45° to 75°  
600 x 350 115 105 95 85 80 70 60 55  
600 x 300 - - 95 85 80 70 60 55  
550 x 300 - 105 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  
450 x 300 - - - - 80 70 60 55  
450 x 250 - - - - 80 70 60 55  
400 x 300 - - - - 80 70 60 55  
400 x 250 - - - - 80 70 60 55  
400 x 200 - - - - 80 70 60 55  
350 x 300 - - - - 80 70 60 55  
350 x 250 - - - - 80 70 60 55  
350 x 200 - - - - 80 70 60 55  
300 x 200 - - - - 80 70 60 55  
250 x 150 - - - - 80 70 60 55  

 

 

 

Severe Exposure > greater than 56.5l /m2 per spell

 Size (Nominal) Min Rafter Pitch
mm 20° 22.5° 25° 27.5° 30° 35° 40° 45° to 75°  
600 x 350 - 130 120 110 100 90 80 70  
600 x 300 - - - - 100 90 80 70  
550 x 300 - 130 120 110 100 90 80 70  
500 x 300 - 130 120 110 100 90 80 70  
500 x 250 - - - 110 100 90 80 70  
450 x 300 - - - - 100 90 80 70  
450 x 250 - - - - 100 90 80 70  
400 x 300 - - - - 100 90 80 70  
400 x 250 - - - - 100 90 80 70  
400 x 200 - - - - 100 90 80 70  
350 x 300 - - - - 100 90 80 70  
350 x 250 - - - - 100 90 80 70  
350 x 200 - - - - 100 90 80 70  
300 x 200 - - - - 100 90 80 70  
250 x 150 - - - - 100 90 80 70