A Guide to Roof Pitch

What Exactly Is Pitch?

• Pitch refers to how much the height of the roof increases for every foot that it travels horizontally. Basically, this tells anyone who understands pitch how steep the roof is. Pitch is normally expressed as two numbers, with the height listed first. So, a roof with a shallow pitch that goes 4 inches up for every 12 it travels across might be described as a "4/12" roof, a "4 to 12" roof, a "4-12" roof or other similar variations.

Measuring Pitch

• To measure the pitch of the roof, you need a level and a measuring tape. Mark the location on your level 12 inches from one end. Hold the unmarked end against the roof in a level position. Then, measure the distance from the 12-inch mark straight down to the roof to find the pitch. You can also get the pitch by using the same method on the bottom of an exposed rafter if you have access to one on an overhang or in your attic. This method is more exact because shingle depth won't throw off your measurement.

Safety

• Roof pitch is important for roofers and amateurs when it comes to planning for roof safety. Anyone that wants to attempt a repair on his own roof needs to consider the pitch before getting on a ladder. For instance, OSHA states that a safety harness must always be worn on a roof with a pitch that is steeper than 8:12. Slide guards are required once a roof reaches a pitch of 4:12. These are guidelines that professionals are required to follow, but do-it-yourselfers should also consider them as good recommendations.

Roofing Material

• The pitch of the roof also informs what type of roofing material works best on that application. A roof with a very steep pitch is not suitable for single-ply roofing products, for example. On very low-pitch roofs, such as those lower than 2:1, asphalt shingles and tiles do not work that well because of all the moisture that may be present on the roof due to the shallow pitch. To use shingles on a low-pitched roof, you have to put a special layer underneath to protect the home from moisture damage.