natural slate roofing
NATURAL SLATE
MINIMUM HEADLAP FOR FIXING SLATES

MINIMUM HEADLAP FOR FIXING SLATES WITH NAILS OR HOOKS

The installation of a slate roof involves a number of aspects that must be considered in the design process. Most significant is the environment, with the two main factors being exposure to wind and rain. The primary aspects to be considered are:

SITE EXPOSURE

Buildings positioned on slopes, hills or coastal areas as well as tall buildings will be graded with higher exposure.

TYPE OF SLATE

Small slates are more suitable for steep roofs, while the more exposed the site and on lower roof pitches, wider slates should be used and the lap increased. (See table)

SLATE LAP

This is established by measuring the roof pitch and considering the rain and wind exposure. Where the thickness of natural slates reduces their pitch by 3O or more, the next lower rafter pitch should be selected to determine the recommended head-lap.

GEOGRAPHIC CATEGORIES OF DRIVEN RAIN EXPOSURE AROUND THE UK

 
 

Sheltered
Less than 33

 

Moderate
33 less than 56.5

 

Severe
56.5 to less than 100

 

Very severe
100 or more

In general any area within 30 miles of a west facing coastline is considered to be one of severe exposure.

driver rain exposure around the uk
SHELTERED/MODERATE EXPOSURE (LESS THAN 56.5L/M2)
SIZE (mm)RAFTER PITCH
20º22.5º25º27.5º30º35º40º45º to 75º85º
600x300--95858070605550
500x30011510595858070605550
500x250--95858070605550
450x250----8070605550
400x250----8070605550
400x200----8070605550
350x250----8070605550
350x200----8070605550
300x200----8070605550

Please note that hook fixings should not be used on any pitch below 25º.

SEVERE/VERY SEVERE (56.5L/M2 OR GREATER SPELL)
SIZE (mm)RAFTER PITCH
20º22.5º25º27.5º30º35º40º45º to 75º85º
600x300--12011010085807065
500x300-13012011010085807065
500x250---11010085807065
450x250----10085807065
400x250----10085807065
400x200----10085807065
350x250----10085807065
350x200----10085807065
300x200----10085807065

Please note that hook fixings should not be used on any pitch below 25º.

MINIMUM PITCH FOR SLATE ROOF

When considering the minimum pitch for a slated roof it is necessary to establish the exposure of the site, the length of rafter and the height of the building.

The recommendations shown above are based on a maximum height to eave of 12m and a maximum rafter length of 9m in moderate exposure and 6m in severe exposure.