Simple Jack Rafters Length Calculation Method Used By My Grandfather - House Framing Secrets

www.homebuildingandrepairs.co... Visit our website today to learn more about roof framing, home building and repairs. This video will provide contractors, carpenters and do it yourselfer's with another simple roof framing formula to calculate the length of your hip jack or fill roof rafters.
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16 times 16 = 256
plus
48 times 48 = 2304
equals = 2560
square root = 50.596 or 4 foot 2 5/8 inches
50.596 divided by 4 = 12.649 for 12 inch on center spacing
50.596 divided by 3 = 16.865 for 16 inch on center spacing
50.596 divided by 2 = 25.298 for 24 inch on center spacing
12 inch on center spacing
50.596 - 12.649 = 37.947
37.947 - 12.649 = 25.298
25.298 - 12.649 = 12.649
16 inch on center spacing
50.596 - 16.865 = 33.731
33.731 - 16.865 = 16.866
24 inch on center spacing
50.596 - 25.298 = 25.298

[@Jay-tk7ib]

Something to remember, once you know your common length difference, you can simply subtract that amount from the length of your common rafters to get the length of the longest Jack rafter. If you're starting from the bottom and going up, the common length difference will be the length of the shortest jack rafter.

[@arsitekpintar]

Great

[@justinowen8749]

How did you get the number for the rise is what I am not sure of like I asked before pitch x itself or pitch times the run

[@justinowen8749]

Where does the 4x 4 come from ? 4 inch pitch x itself or 4inch pitch x 4’ run

[@justinowen8749]

And then do you divide the longest jack rafter by the number of jack rafters or is it always divided by 2 3 and 4 for 1’ oc 2’ oc and 16” oc

[@justinowen8749]

So if it were a 5/12 would it be 5x 5 or 5x 4

[@justinowen8749]

So how did you get the number 16 ? If it were a 5/12 would the # be 20 or 25

[@vivalaleta]

Mr. Van, I have a question about architecture that is mostly about appearance. The house we are buying is a small farm house with a lean-to addition on the front. We want a smallish mudroom/wood storage room built on the front of the lean-to but can't figure a way to make it look right. Any ideas?

[@Outrunninaround.]

Rafter spacing divided the cosine of the rafter angle. 📐 this is the difference in length jack rafters decrease by size as they go down. 16/ cos18.43 degrees = 16.86” then subtract the 1 1/16. This is where your 45 degree bevel intersects.

[@fasteddie8782]

The best thing would be to figure out before you lay your wall so too so you have something underneath them but you got to remember that's to the center of where a 40 will be nice to use a 48-inch hypotenuse so you could use one sheet of plywood and just measure it down to nothing and have a fit perfect no waste at all and the other cut will fit in the other side but I wonder on the difference in lengths of Jack wrap this is that one foot four and 7/8 the same as the first line under a four pitch on a framing square just wondering what good video man I liked it keep up the good work

[@gozo165]

Love your videos. I would like to clarify the length of the rafter, which is 4' 2 5/8" = 50.625" in

[@andygrossauer8192]

How do much do you adjust the rafter length to account for the birdsmouth?

[@jasonhayes5036]

5/8 to decimal is .625

[@pcatful]

I think you don't talk about why dividing it into equal units works. I don't see you explain that these sloped triangles are similar triangles and so the sides will have a direct proportional relationship.