I have a student who is going to write his red seal exam in carpentry and a couple of questions ask you to use what is called a ” slope gain factor” does anyone know what this is,Ii see on some of the curriculum documents, but no explanation or how to? any help would be great.
Thanks Darren
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Replies
Must mean that the questioner is facing uphill.
:-)
Any questions having to do with carpentry and geometry can be presented by using right angles, specifically right triangles. Don't let a peculiar term confuse you.
BTW, I've never encountered that phrase. Sounds more like something a surveyor might say, particularly if he wanted to impress the client.
Edited 11/12/2008 3:59 am by Hudson Valley Carpenter
Ironically, this is from an internet scavenger hunt site:
http://forums.intpcentral.com/showpost.php?s=afbfb8e83e73671f563cc57d64730f3c&p=919925&postcount=160
edit: see item 10 on the list.
Edited 11/11/2008 4:29 pm ET by Ten_Thumbs
I'll bet that is has to do with rafters and a framing square.
Slope gain factor might be the length, per foot of horz run, of a rafter, given the slope.
Length of rafter per foot of run for a given slope.
Any good framing sq. has the information stamped into it
http://en.wikipedia.org/wiki/Carpenter%27s_square
or you can calculate it for 1 ft. of run and skip the square.
With the numbers in tables on the framing square for "Common Rafter Length Per Foot Run", you multiply them by the run in feet to to get your answer. For example using a 5/12 pitch roof, the table says 13, which is the hypotenuse for a 12" run, 5" rise.
If you had a 10' run for a common rafter.
You will multiply 10 x 13 = 130". That's your rafter length.
Some people use the "Slope Factor" instead. All that means is that you take any number on the framing table for the common rafter and divide it by 12, that gives you the "Slope Factor".
5/12 pitch has 13 in the table like I used above. 13/12 = 1.083333
Take that number and use the same 10' run in inches (120)and multiply the slope factor.
1.083333 x 120 = 130"
Another example is for an 8/12 pitch roof with a 10' (120") run. Under 8 on the framing square is says 14.42".
14.42 x 10 = 144.2" (Common Rafter Length)
14.42/12 = 1.201667
1.201667 x 120 = 144.2"
Hi Framer!
After my lessons from you, Joe, Piffin, and Arcflash, I took a poke at " Slope Gain Factor " After posting, I went back to the site and found that you had posted just in front of me. Of course, you were simple and right to the point, where I rambled like a tumble-weed. I'm still grateful for the help you guys gave me, and, your right, This is fun!
The Square Root of the Sum of the Rise squared Plus the Run squared, Divided by 12. Example: In a 5/12 roof, 5 squared = 25, + ( 12 squared= 144 ) = 169. The Square Root of 169 = 13, (which is how much gain you get per foot of Run) Divided by 12 = 1.083333333, (which is how much gain you get per inch of Run). I know this Factor as the Rake Multiplier, such that if you had a Run of 39.25" X 1.083333333 = 42.52083333" which reduces to 42.5" which in turn becomes the length of the Common Rafter. This is short by 2/3 of 1/32 of an inch, which means that on your test, you may have to settle for an A-
Hip/Valley Rafters are a little more testy, and it's common to figure to the 32nd of an inch. So, instead of using 5/17, use 5/16.97056275. Everything else is the same: 5 squared = 25, + ( 16.97056275 squared = 288 ) = 313. The Square Root of 313 = 17.69180601, Divided by 12 = 1.474317168, (which is your Slope Gain Factor per inch of Run). I know this Factor as the Diagonal Multiplier, such that using the Run of a Common Rafter as stated above, 39.25" X 1.474317168 = 57.86694883" which reduces to 57.875" which in turn becomes the length of the Hip/Valley Rafter for the same 5/12 sloped roof.
Overhangs are figured the same way. If for example, on such a small roof, you are required to overhang 6", you would multiply 1.083333333 X 6 = 6.499999998" which reduces to 6.5" and then added to 42.5" which = 49" for a Common Rafter.
Likewise for a Hip/Valley Rafter it would be 1.474317168 X 6 = 8.845903007" which reduces to 8 - 27/32" ( 8. 84375" ) and then added to 57.875 which = 66.71875" ( 66 and 11/16 strong ) or 66 and 23/32
Go for it!
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Thanks for your help, I have framed alot f roofs always using the step off method or the line length calculation from the sq, I was asked to tutor this student ( same experience as me just sllightly younger) who is challenging the red seal exam in ontario. Mostly math related questions he was stumped on and then this slope gain factor came up and had me stumped , glad to see simple solution, I tried it on all the test prep questions and worked well, the unfortunate thing with this exam is that it is in metric which throws a wrench into your thinking process.
Thanks to all who responded
Darren
""unfortunate thing with this exam is that it is in metric which throws a wrench into your thinking process."" Maths the same. Funny though I have never thought about whether there are framing squares in Europe or other places that have the same scales on them in metric.
They can't get your Goat if you don't tell them where it is hidden.
A garage has a roof with 1:4 pitch this roof will have a 45 degree slope gain factor of .....
im going to write my red seal and i dont know where to start to figure out this question can anyone help???
A garage has a roof with 1:4 pitch this roof will have a 45 degree slope gain factor of .....
You must be talking about a hip/valley rafter?
Slope Gain Factor
The slope gain factor represents the lenght gain along the slope for each unit of rise ,Mainly used to understand how to create a roof system basically the unit of rise for every unit of run so if you have a 5/12 pitch you can determine how much length it would require
angel
"The slope gain factor represents the lenght gain along the slope for each unit of rise"
For each unit of RUN, no?
If you take the number off the framing square (unit rise), you multiply it by the length of run to figure the rafter length.
Framer above explains the original question (slope gain factor) well. One we are used to (framing square calc for length of rafter) and relates that to the slope gain factor to figure out rafter length.