Roof Slate for Low Pitches
In this article, we will breakdown the use of natural slate on what is deemed to be a “low pitched roof” – 22.5 degrees or lower. With this information, you should be able to make an informed decision on which slate to use, or whether you use natural slate at all (fear not, natural slate can be used on pitches as low as 12.5 degrees. More information on that later).
There are many variables that need to be taken into consideration when choosing the slate, or even deciding whether slate is a viable choice.
Consider your rain exposure
Moderate Exposure: (Driving Rain index less than 7m2/s). Severe Exposure (Driving Rain index greater than 7m2/s)
Weather tends to be more severe towards the West. Central UK and, in particular, the East, have been somewhat blessed with lighter wind driven rains. The below graph should give you an idea of your exposure.
Consider the size of the slate
The wider and longer a slate, the lower the pitch on which it can be successfully applied. The table below show the recommended headlap for your slates (in mm) for a MODERATE EXPOSURE area.
20 Degrees | 22.5 Degrees | 25 degrees | 27.5 Degress | 30 Degrees | 35 Degrees | 40 Degrees | 45 Degrees | |
---|---|---|---|---|---|---|---|---|
Slate Size (mm) | ||||||||
600×300 | 130mm | 115mm | 90mm | 80mm | 75mm | 75mm | 65mm | 65mm |
500×300 | 115mm | 105mm | 90mm | 80mm | 75mm | 75mm | 65mm | 65mm |
500×250 | 125mm | 110mm | 90mm | 80mm | 75mm | 75mm | 65mm | 65mm |
450×250 | 125mm | 110mm | 90mm | 80mm | 75mm | 75mm | 65mm | 65mm |
400×250 | – | – | – | 85mm | 75mm | 75mm | 65mm | 65mm |
The table below show the recommended headlap for your slates (in mm) for a SEVERE EXPOSURE area.
20 Degrees | 22.5 Degrees | 25 degrees | 27.5 Degress | 30 Degrees | 35 Degrees | 40 Degrees | 45 Degrees | |
---|---|---|---|---|---|---|---|---|
Slate Size (mm) | ||||||||
600×300 | – | 120mm | 120mm | 115mm | 110mm | 90mm | 80mm | 70mm |
500×300 | – | 125mm | 115mm | 110mm | 110mm | 90mm | 75mm | 65mm |
500×250 | – | 135mm | 115mm | 110mm | 110mm | 90mm | 75mm | 65mm |
450×250 | – | – | 115mm | 110mm | 110mm | 90mm | 75mm | 65mm |
400×250 | – | – | – | – | 100mm | 95mm | 75mm | 65mm |
As overwhelming and complex as this seems, we operate on a much more basic rule. Don’t use natural slate below 22.5 degrees, unless you have the ability to hole the slates. All of our 500×250 slates are holed at 190mm/195mm. suitable for pitches as low as 22.5 degree and upwards. For shallower pitches, we have unholed 500×300 slates which are suitable for 20 degree pitches (based on a headlap of 115mm). Our 600×300 slates are typically holed at 230mm, suitable for pitches down to 22.5 and upwards. Please call us as these holes can vary ever so slightly.
Can I use natural slate on a pitch lower than 20 degrees?
YES! There is now a product called “Easy Slate”. Easy slate is, basically put, a plastic gasket that sits between the slates, sealing the gap and creating a seamless course of slates. This product will allow for natural slate to be used on pitches as low 12.5 degrees. Call us on 01296 658 396 now for further information.