A roof is a roof, except when it comes to pitch and all that is affected by it. Pitch or slope, which is the angle at which a roof rises, can be considerably different depending on the style of the building and it is important to know for a number of reasons. Since angles usually come into question whenever cleaning, repairing or replacing a roof, having such information readily available can be very helpful. Some important components to consider are listed below.
- Material – Certain material is only fit to be used above a certain angle to prevent premature decaying from water and sitting debris. As far as working on a roof is concerned, the higher the pitch the more dangerous and time-consuming the work, generally requiring the use of safety gear for protection when the intention is to climb onto the roof and stay there.
- Estimate – When homeowners call about having a roofing job done, contractors may ask ahead of time if the pitch is known, so having that information available can be very beneficial. Of course, obtaining the measurements can be a bit tricky unless such data has been recorded elsewhere from having previous work done.
- Determination – Pitch or slope is determined with a ruler and a bubble level, being measured either somewhere on the top surface or under the rafters. While each method presents its own inconveniences and difficulties, the under rafter measurement can be taken in an attic with exposed rafters or under an overhang at the edge of the roof. For a measurement from on top of the house, someone needs to be up on the roof or at least on a ladder that has a great enough reach.
- Calculation – Regardless of which way it is done, the calculation is the same. Using the level, align it with one end touching the roof surface,or the underside edge of a rafter, then angle it so that the bubble is centered and the level is even. With the ruler positioned at twelve inches out along the level, measure from the roof’s top surface to the bottom of the level or alternatively from the rafter edge to the top of the level. It is critical for an accurate calculation that the measurement is recorded at the twelve-inch horizontal mark along the level, since twelve inches is the basis of the pitch comparison.
- Angle – The pitch or angle is then the number of inches measured from the surface to the level. It is usually recorded as a fraction, such as 6/12 (six over twelve) if the rise is six inches along every twelve inches of length, and so on. Sometimes it is recorded as 6 to 12 or even 6 – 12.
- Slope – In some circumstances, the slope is recorded as a percentage. In this case, 6/12 as a percentage would be a fifty percent slope. This number is calculated in the following manner: six inches over twelve inches which is the same as one inch of rise per two inches of length (twelve divided by six) or 6/12 = ½ = 50 percent.
- Classification – When classifying pitch, the National Roofing Contractors’ Association (NRCA) refers to the following: A low slope/pitch is anything three inches in twelve inches, fourteen degrees or twenty-five percent; a steep slope/pitch is anything greater than three inches in twelve inches, fourteen degrees or twenty-five percent. Flat roofs generally incorporate a very slight slope of only two to four percent to aid in drainage and prevent ponding.
Determining the slope or pitch of a roof is an important thing to know, especially when it comes to deciding which material to use and what plan of attack to take for repairs, routine maintenance, or just regular inspections. Knowing this calculation allows for maximum safety whenever a roof is involved!