Slate Roof Pitch Minimum

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.

Slate roof pitch minimum.

Higher exposure or different sized slates necessitated a greater roof pitch of 22 5 or more. It is uncommon to find a roof below 15 but for those very low pitch applications there are interlocking clay pantiles available suitable for use down to 12 5. Our suggestion is not to contemplate using slates on roofs with a pitch less than 20 degrees and then only for big format slates eg 500x300mm. You consider some alternative solutions.

But since there is still a wide variety of slate roofing systems there are occasions when the minimum pitch can go down to as low as 15 0 depending on the uniqueness of the roof. It is agreed that the roof pitch should be a minimum of 20 degrees preferably a bit more. Conventional low pitch slate roofs are recommended down to a minimum of 20 in areas of sheltered or moderate exposure providing a 500x300mm slate is used and a headlap of 115mm. Traditionally a minimum roof pitch of 20 was recommended in bs 5534 but modern tiles and slates have now been designed for applications as low as 15.

A couple of likely slate suppliers are consulted and they confirm that they are happy to supply 600x300mm slates for a minimum roof pitch of 20 degrees assuming a minimum lap of 125mm.