0
This is an application of Pythogoras' Theorem relating to right-angled triangles
A 3-12 roof pitch is a rise of 3" inches for every 12" run in to the centre or edge of the roof
so applying Pythagoras' theorem we get a right angled triangle that has one edge that is 12" long (a) and another edge that is 3" long (b)
We need not worry with the hypoteneuse, but we do need to concern ourselves with the Tan of the angle opposite line b.
The Tan of this angle is 0.25. the angle therefore is equal to arcTan or Tan-1 of 0.25 which is given as 14.04o to 2 decimal places
Still curious? Ask our experts.
Chat with our AI personalities
Steve
Blake
Maxine
Add your answer:
Earn +20 pts
What does 3 and 12 mean?
It is usually referencing the pitch of a roof so a 3/12 roof would have a rise of 3" in a 12" span..... jimmyrjii
How may degrees between hour 12 and hour 3?
The angle between 12 o'clock and 3 o'clock is 90°
What is the difference between thread angle and lead angle also clear it from diagram?
A thread angle is the angle of the threads relative to the shank which is 60 degrees for unified screws The lead angle is the pitch of the screw divided by the circumference of the shank; it varies but is around 3 degrees
How do you figure the angle to cut trusses?
You will need a Framing Square. Decide what pitch roof you want or need. Steeper the roof, the more weight it will carry. 3 x 12 is minimum, 5 or 6 by 12 is better. Take a rafter, the top board of the roof frame, long enough to cover the distance you need. Lay the rafter flat with one end in front of you and the length of it towards your right. Lay the square on the rafter, corner pointing between your feet, long side on your left, short side on right and pointing away from you. On the bottom edge, the side closest to you, set the square on 12 inches. On the short, right hand side, set it on 3, 4, 5, whatever slope you have chosen. With the square in place, mark the back side closest to you on the rafter. This will give you the end angle of the rafter. Where you will put the fascia when trimming.You will need to figure how long a rafter you need to meet in the center. This will vary depending on angle of the roof, Steeper the pitch, the longer the rafter will be.On the end where you started, you will need to allow for the overhang where the soffit will be. This is a variable also. To allow for a 12 inch overhang, use the square again after you have cut the end of the rafter.Using the inside of the square this time with the point facing away from you, put the short side on the cut end of the rafter and on the long side mark the bottom of the rafter at 12 inches. At this point using the same angle as the end of the rafter, you will need to make a notch up of 1 1/2 inches using the square on the side away from you with the point away from you. The notch should be 1 1/2 high and maybe 2 1/2 long depending on angle of rafter.This only gets you the rafter for the left hand side. Generally the same on right hand also, still will need to figure cross bracing. That depends on width of roof and pitch. Steeper the pitch, the less bracing needed. All roofs are different.Rafters are easy to do, just takes a bit to describe and try to make sure all steps are covered and clear. Hope this helps.
Sam wants to tile the roof of his shed with square tiles that are 4 inches square His roof is 12 feet by 12 feet How many tiles does he need?
If the tiels do not overlap (shingles overlap) one square foot will be covered by 3 * 3 = 9 tiles12 * 12 = 144 square feet144 * 9 = 1296 tilesSam should get at least 1300 tiles because he is sure to break more than 4!This assumes that the roof is square and flat.
