Construction and building inspectors use advanced math. this is always a "right triangle"- angle bc in our sketch) allows use of sine and cosine tables to obtain the lengths of the two unknown sides b and c in the sketch. Why not just use a rise run calculator on-line to get the angels, slope, pitch? Civil engineers plan, design, construct, and maintain public works, such as roads, bridges, and harbors. I used an online calculator available at http://www.creativearts.com/scientificcalculator/ and the simple formula shown in my illustration. Could we calculate the tangent of 38 degrees? Try to take math through Trigonometry. Using a calculator and it's square root function, and the most basic knowledge of geometry is not enough - we also need a table of sine and cosine values, functions readily found these days online. If you WANT a long horizontal run, you could drop the rise to a minimum of say slightly under 5 inches, you'd build (79 / 5 ) = 16 steps. However, most calculations are made on right triangles because any triangle can be converted to a right triangle through bisection. Building inspectors are incredibly essential professionals because their work keeps us safe and keeps residential and commercial builders accountable for their quality of work. Thanks, RalphThanks for asking an excellent question: to have space and to add an illustration I repeat your question and answer it at the bottom of the article above. depends on how you're building the stairs. Knowing that the triangle abc will always include a 90 degree right angle ( i.e. We know bc is always 90 degrees. You can do this using a transit, a protractor or other angle measuring tool either by placing your angular measuring tool on the sloped surface of the stringer side a, or by actually measuring the angle formed between side a and a horizontal or level surface. Will 5G Impact Our Cell Phone Plans (or Our Health?! Choosing a stair tread depth (step run length) of 10" in the equation above gave us a calculated individual step rise of 7.8". Main Number (904) 255-8500. But the rub is that we need to know at least two of the angles on this triangle. Divide your total rise height (say 116") by a typical step riser (say 7") and get 16.5. For any stairway of a given angle or slope (say 38 degrees in your case) the ratio of run (x) to rise (y) will remain the same. Approximately 50 different jobs in categories including management, farming, professional services, administration, construction, production and installation use trigonometry. Fact Check: What Power Does the President Really Have Over State Governors? The slope of your stairs is given as 38 degrees. Suppose we measure angle ab (sketch above) at 30 degrees. . - George Tubb. Move the side joist as necessary to make the diagonal line exactly 10 feet and you are guaranteed that the side joist is at a perfect right angle to the building - a nice way to decide how to locate deck corner post piers. Early astronomers noted fixed relationships between the sides and angles of right triangles. Construction and building inspectors use advanced math. We also discuss stair step rise & run calculations when we are given only the slope of a stairway, and we explain how to use the tangent function to convert a measured angle into stair step rise & run dimensions. ... My greatest areas of specialty are Algebra, Geometry, and Trigonometry." I found some where you can simply plug in the rise and run and everything else is calculated for you. For an outside stair stringer the stringer depth (2x?) The tread rise (for which we are solving the equation) is the blue Y at the left of the sketch. Festival of Sacrifice: The Past and Present of the Islamic Holiday of Eid al-Adha. Height Y1 / Length X1 = Height Y2 / Length X2. We'll call the run of 7 ft. run of the stair triangle ADJACENT side (because one end of it touches the angle we want to find. Etc. 101-A& 101-B (may appear as ANSI B101.0) sets rules for measuring walkway slip resist, OSHA - (Dept of Labor CFR 1910.22 does not specify COF and pertains to workplaces) but recognizes the need for a "qualified person" to evaluate walkway slipperiness, ADA (relies on the ANSI and ASTM standards)Â,  "Right Triangle Angle And Side Calculator", csgnetwork, retrieved 9/29/12, original source: http://www.csgnetwork.com/righttricalc.html - Example: if our stairs are to run from the two extreme ends of the 2x stringer we illustrate at above right, and if that length (after cutting to "fit" the hill and desired stair run) measured 100 inches exactly, using just that known length of the hypotenuse of the triangle we would obtain the key measurements of stair rise c and stairway run b by first converting all measurements to inches and then using a table of sine and cosine values. Now divide 116 / 16 = 7.25 - that's your uniform step riser height. , my riser is 116" how many stairs do i need and how long will my stair stringer be. Robert: I think by "run of 18" " you refer to the read depth from nose to riser. A tangent is the ratio of two sides of a right triangle: specifically the height (Y) divided by the base or length (X). if I have a 7ft run, with 2 ft rise , what is the angle? And so the three angles formed by the triangle's sides are ab, bc, and ac. There is a 120'' high floor/ceiling and want to build a 6'' inch steps at 36% angle, what is the floor measurement I need? Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia. Triangles & geometry in building framing: This article describes how we can use a simple tape measure and basic aritematic in framing a building deck, floor, wall or roof to get it square and straight.How to Use the 6-8-10 Rule to Square Up any Deck, Wall, Floor, Roof.