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The pitch of a roof is the ratio used to determine how steep a roof is. It is a vital measurement, which helps you work out the total area covered and how much of an overlap is needed across the individual slates.
The pitch is the ratio based on the rise of the roof (vertical measurement) compared to the run (horizontal measurement). It is common practice to use a 12-inch run measurement.
Measure 12 inches (30.5cm) on a level surface
Using a length of material to act as a marker, make a mark 12 inches (30.5cm) along. The level you use later may have a ruler on the side, but this way, the mark will be more visible to ensure accuracy.
Set up the ladder and climb to the roof
Make sure that you place the ladder on solid, flat ground and ascend to the roof. Firstly, go up unhindered without tools to check that the roof is safe to be on. Once you are happy, collect the tools you need and climb the ladder again. Use a bucket or tool belt so that you can move unhindered.
Use your level to measure the roof run
Whilst holding the tape measure – extended to around a foot or so – place the level on the bottom corner of the roof and hold level. You should be able to see the mark on the level which you made earlier. Keep the far end against the bottom corner of the roof by pivoting up and down until level.
Measure the height
Once the level is in place, hold your tape measure above the 12 inch mark. Hold it at the roof level directly above this, then you can use the weight of the tape measure as a plumb to make sure that the tape measure is perpendicular to the level. The measurement given is the rise, so remember it and write it down.
Calculate the roof’s slope
The number you measured with the tape is the roof’s rise – the amount the roof rises across the 12 horizontal inches. E.G. If you measured 7 inches high, then the roof’s ratio is 7:12
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