How to cut Rafters the Right length the first time

so in case any of you are wondering how to figure out the length of a rafter get my calculator so building an addition on my house that's on my channel that this is posted on so I have an addition that's 16 foot three quarters of an inch wide I don't know how I ended up with the three-quarter that's framing to framing so I have a half inch OSB on there too I'm not going to consider the thickness of that because my OSB doesn't go this high so this is going to go right up against the bear framing so first thing I did well I take my so I take half of this let me get rid of that so I split this in half so that's going to be 96 because I'm going to inches 96 and 3 8 okay then I have to subtract half of the Ridge board well I have to subtract this five and a half the thickness of my wall because I want this point to this point to here so I want this length the hypotenuse of a triangle remember from your school days a squared plus b squared equals c squared plus I have to subtract three three quarters of an inch so um if you don't know how to change a fraction to a decimal is very simple the three-quarter most of the three eighths I know three quarters so three I don't know if you can see this three divided by eight point three seven five so that's going to be five thousands 5.5 as you would know and 0.75 okay so first 96.375 minus five and a half for the wall minus the ridge the this half of the ridge it's 90 .125 now if you want to get that back to fraction subtract 90 so you have just a decimal there multiply it times 16 to give you 16. 2 16 1 8. so this is 90 and an eighth okay so now I have my length of this side we'll call this a okay so we have 90 we're going to go back to that decimal for a minute because we're going to do this squared now how tall is this my pitch is for every foot that I go over I go up six inches so I'm going to take this number 90. and an eighth I put 90 and 125 thousands divided by 12 the 12 inches 7.5 decimal times six that is the rise so I end up with 45.0625 so let's get rid of the 45 and multiply by 16. that's 1 16. so now I know that my bridge board from the top of my wall to the bottom of my Ridge board is 45 and a sixteenth so let's put that back um so plus 45 and yeah what did I say that was um 90.125 divided by 12 times 6. oh yeah uh zero six two five okay now that's got to be squared okay so 90.125 now if you're not familiar I mean if these are simple calculators you can square it easy push this thing is called a carrot and squared and it equals eight thousand one hundred and twenty two point five one we're just going to stop at it there then we're going to take the next measurement 45 point zero six two five squared equals two thousand Thirty point six three we'll go with so we add those together plus 20 30.63 equals ten thousand one hundred and fifty three point one four and now we have to have the square root of that so there's a square root button you must push the second button first and it's above that one and then you put your number then 10 153.14 equals so the square root of that is 100 .7627 we'll say let's get rid of The 100 we have the 0.76 times 16 because 16 so I only care about 12 16 100 and 12 16 which is what three fourths right 103 4. you want to reduce it divide both sides by four right divide not multiply anyhow divide so now we know I know that my rafter length in this bottom side this triangle right here is 103 quarters of an inch 100 inches and three quarters that's how you do it again it's not hard simple math but it's an easy way to not waste Lumber you're buying something longer than you need especially the price of lumber now I don't know what they are where you are but so this is 86 this is uh eight foot four right eight foot four and three quarters so I'm just buying a 10 footer and then whatever my overhang has to be I'm not going any longer than that that should be plenty eight foot four to there plus this and it'll be six inches or more nice to me nine I may only have seven or eight inches of roll ring but I don't care I'm not gonna buy a 10 footer just so I can have a photo right um and I actually will buy some of that lap siding that comes primed it's got wood grain on it because that's what I have in the rest of the house I use that for a fascia board because Pine is not great here um the sun kills that and the stuff that I'm getting is OSB base thing it's I don't know how good it is we'll see so anyhow that's how you do it I'm actually using a two by six I didn't draw this to scale this is not to scale I used a 2x6 for a Ridge board and a two by six right here so I'm going to keep it flush with the bottom because as you know when you cut an angle on something it makes it longer right that cut I want a space here so my air my air vent is not blocked with the ridge I want a good good amount of space there so that's it next I'll be cutting them out when I get home so here we are at the lumber pile I'm gonna cut out a rafter we just finished this short video just so I know I remember we went through all this and I ended up with 103 inches so first thing you want to do when you're cutting rafters I'm gonna use the pattern so I want one that's really really straight because once I make mark one I'm gonna cut them all and then if there's a crown that means the bow if the top the upper part you mark this as the top okay now I said that there was a 612 pitch so speed square and you go on here you want to get it just as close to the end as we can so 6 12 here oops 6 12 here sorry should be 22.5 degrees oh 27. all right man either way 26 degrees so that's that cup let me go in here to the and I always want it this way a hundred and three quarters to the bottom of that I'm gonna mark it but I'm gonna check it okay 103 quarters just kind of go this way to double check because twice a lumber you know 103 quarters of an inch so that's it right there that's the bottom of our cut so now if I have let me say it was 20 26 degrees so if it's 26 degrees and what's the angle of that well it's 90 degrees minus 26. so it's 64. 64 and 26 is 90. so we're going to go down here and go away over here at 64. that's the top of the wall and then that's five and a half if you remember my wall thickness is and then this is back to the sixth pitch on this part if you have to look on the square this is a six pitch but for a valley rafter it's over here six pegs just a little bit longer because it's um well it's at a 45 Volta at whatever degree it is 45 yeah so that's it and I cut my tails off so this is called a bird's mouth so I cut my tails off later so I can snap a line down there and cut them all the same see I could actually really get like an eight inch overhang I think that that would be a little seven or just in case that soffit material is only seven and a quarter instead of eight same pitch six one more line you can also use a framing square and do put stairs stair tread a sterilizer shoot stair stringer um gauges on

Channel: Mike's Madness

Views: 33,494

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Id: 2unfVdPWnAU

Length: 10min 56sec (656 seconds)

Published: Sat Dec 10 2022