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.
Maximum pitch for slate roof.
As per the nrca roofing and waterproofing manual fifth edition they recommend that roof deck slopes intended for the application of steep slope materials at 4 12 18 degrees or greater page 405.
11 august 2015 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.
The slope of a roof is often referred to as the roof s pitch.
Roof tiles and slates are very versatile products and can be used on a variety of roof pitches.
It is agreed that the roof pitch should be a minimum of 20 degrees preferably a bit more.
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.
Generally a slate roof is not installed on a pitch less than 4 12.
What is the maximum roof pitch for a roof tile.
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.