Measuring for pitch is a simple process. This article is intended to explain the basics, then discuss issues not often addressed. Let’s jump right in!
The Necessary Tools To Measure The Pitch of a Roof
A level at least 12 inches in length, tape measure, and approximately a three-foot-long 2×4 piece of lumber.
Making The Pitch Measurement
All MicroMetl pitched curbs are constructed using customer provided height & pitch, combined with a 12-inch reference — e.g. 1/4″ in 12″, 2″ In 12″, or 3-1/8″ in 12″. The 12-inch designation is NOT measured upon the surface of the roof as shown in Figure #1A, but perpendicular to the ground using a level as in Figure #1B.
As previously noted, the level must be at least 12 inches long. Measure and mark off 12 inches from the end of your level – Figure #2. Holding the edge of the level on the roof, lift the other side until the water bubble of the level is centered (perpendicular to the ground). Using the 12-inch mark, measure directly down to the roof… That is your Pitch measurement.
You may be thinking, My roof has shingles or imperfections which could alter the pitch measurement depending upon where I measure, will that affect the measurement — Yes! Remedy the problem using a quality three-foot 2×4 piece of lumber. Lay the 2×4 along the pitch Figure #2 to average out the surface imperfections, and make your measurement upon the 2×4.
Applying Your Measurements To A Pitched Curb
Each manufacturer’s curb is different from its competitors… Mostly the locations of the supply & return openings as well as their orientation. Once you’ve made your measurements, how do you practically apply them to a pitched curb?
Once you have determined the brand and model RTU you want to install, go to the manufacturer’s website and seek a layout of the curb. As for MicroMetl, simply contact our Customer Service Department to receive a worksheet specific to your RTU as displayed in Figure #3.
It is important to note, the graphical arrow accompanying the word “Pitch” on each Illustration in Figure #3 is pointing to the apex or top of the roof.
Making The Pitch Measurement – The Alternatives…
I Only Have The Angle of the Roof
No Worries… This will take some basic trigonometry but can be calculated with accuracy. Figure #4 is a visual example. Let’s assume the angle is 18.5 degrees. We know that the standard measurement of 12 inches applies to the top of the triangle in the example.
Without getting into the specifics of trigonometry, using a calculator the formula is 12 (Inches across the top) times the TAN (Tangent) of 18.5 degrees, which equals 4.0. Therefore the pitch of the roof is 4 Inches in 12. Here’s a better breakdown… 12 x 0.334595319 = 4.015 (Round To 4 Inches).
I Need The Angle of the Roof
Perhaps you need to develop an angle measurement. Again, you’ll need trigonometry available on most calculators. See Figure #5… Using the standard 12 inches applied to the top of the triangle, and the four-inch measurement designating the roof slope, use the following formula — The 4 Inch Rise Divided By The 12 Inch Top Span. The result of that is applied to the Trig function of TAN-1. The breakdown is… 4 Divided By 12 = 0.0333333333. — 0.33333333 applied to TAN-1 = 18.435 degrees.
I Need Measurements And Lack The Necessary Tools – Improvisation!
Someone Borrowed My Tape Measure — Now What?
This sounds silly, but we all get into measurement estimations from time to time. The moment you realize someone borrowed your tape measure and didn’t return it is one of them. Here’s a suggestion… Pre-measure body parts! Break out a tape measure to discover which finger joint is the closest to one inch; Which finger is closet to three inches; Measuring from the joint of your arm to the wrist or a line on the palm of your hand to equal one foot. What is the EXACT length of the sole of your work or dress shoes? This sounds ridiculous, but regardless of what you use as a reference, have ACCURATE references. Estimating your toe to heel measurement is 12 inches when it’s actually 10.5 inches will equate to a gross over-estimation of length when attempting to measure a large area.
I Don’t Have a Traditional Level
If you don’t have access to a level, use a clear glass of water. Using a permanent marker and clear glass, make a straight reference mark all around the glass. This can be done by setting your hand on a stationary surface and spinning the glass to properly mark it. Set the glass on a solid surface 12 inches or longer and substitute this for the level. The fun is in keeping the glass from falling off the surface!
I discovered a video on YouTube called “Level Anything With Water” using water and a clear tube. Water pressure will always level against itself when inside a tube. This technique is best when the two points you want to level are at a distance. However, it will work.
The Curb Pitch Measurement Was Wrong And So Is The Curb… What Do I Do?
So what’s the big deal if an RTU’s not leveled! I’ve heard this comment before. Here’s why… Like your car, the motor inside the compressor requires oil. If the oil level inside the compressor is not level, this can lead to one side of the compressor’s motor not being properly lubricated. Ultimately, that will cause compressor damage due to the grinding of the motor’s moving parts, overheating, and a reduction of efficiently.
If you haven’t cut the opening in the roof yet… Don’t! Order a new curb. If the angle is slightly off, you can install shims to compensate. However, if the angle is too steep, don’t install the RTU. Cover the opening and order an angled Curb Adapter.