How To Measure
Roof Pitch / Slope
If you cannot measure the
height of a roof accurately, the next best way to measure the
roof pitch on an existing building is with a 48" level and a
tapemeasure.
Roof pitch or slope is usually
expressed in as "X/12" or "RISE over RUN"
Carefully climb onto roof
(ensure to use proper tieoff methods or scaffolding) and
hold a 48" level so the bubble is in the middle. This will be
your RUN.
Next, measure from the end of
the level down perpendicular to the top of the roof. This
number will be your RISE.
Take this number and divide
mathmatically by 4 to get your pitch. This only works with a
48" level. If you are using a 36" level, divide by
3.
For example, if you measured
40" perpendicular from a 48" level then your pitch would be
(40" / 4 = 10) and (48" / 4 = 12) or 10/12.
If you measured 24"
perpendicular from a 36" level then your pitch would be (24" /
3 = 8) and (36" / 3 = 12) or 8/12.
For accuracy, we do not
suggest using a level less than 36" long.
