How To Cut Perfect Rafters

this is for the people that are specifically wanting to build a post-frame porch like we do where we use purlins this is good if you're going to do a rafter every two feet and then she's right directly on top of it hey what's up guys welcome back to the channel so behind me you'll see a porch that we have all of our kind of our wall post header Framing and we're ready to build the roof now we do it a little bit different just because we're in the post frame you know sector but the theory and the method in the mathematics behind how we cut our Rafters are pretty much Universal and I want to take you guys through that so this video could be for somebody that has never cut a rafter or it could be for somebody that just does it kind of the old-fashioned way where they they don't really know the math and nobody taught them that so they just pull their tape measure out they get a measurement for what they think they should be cutting and then they just kind of cut it and fit it and go on about their way so if you don't know the rafter is the thing that actually supports the roof it's the it's the angled board that has a couple weird cuts and usually requires a little thinking so that's what we're going to talk about today and uh we're going to show you some math don't be don't be alarmed you don't have to do too much thinking if you have a good calculator on your phone so let's go ahead and get into it now I don't know about you guys but I although I can conceptually learn things I also like to see them on paper or in real life before you know it really gets to memory so we're going to go ahead and do a quick drawing and I'm going to show you um how this works so what we're going to do is first we have this line here this is going to represent our wall okay and then we're going to have this line here and this represents the top of our header now we're using a cedar header six by six but this doesn't really matter this is just conceptual knowledge right and what we're looking to do is we're going to look to cut a rafter in so this is not always going to be to scale but let's see how do we do this okay so here's my rafter and whether you're building stick frame post frame it doesn't matter this this theory is still going to apply now what I need to know is that I already know this right here this is nine foot in my application okay I know that's nine feet because I've already measured it and I also know the pitch of my roof is 4 12. now if we remember back in math if we know a couple of these Dimensions we can figure out what this diagonal Dimension I I know what to cut that at I know what this height is so I know where to set this on the wall exactly and I'm going to show you how I do that so we're going to open up the Construction Master Pro now like I said I know that my this is what it's called okay we're going to give you a couple more terms so that you understand what I'm doing this I think that's spelled right I don't know that is called diagonal okay that is this bench in here and then this nine foot this is called our run and this is our rise now those are just like mathematical terms and also that is the terms that we have here to use and the buttons in our Construction Master Pro so what I'm going to do is enter in nine feet run and I know that I have a 412 pitch so you see that so what I'm going to do is I'm going to type in 4 inch pitch so it's a four inch out of 12 inch rise run okay that is going to give me a diagonal dimension of nine foot five thirteen sixteenths so now I know nine foot five thirteen sixteenths is this dimension and my rise is three feet all right so basically the important thing to note here guys is that once you have either two of the four dimensions run rise diagonal or the pitch of this triangle you can figure out the other two with the calculator app so I definitely recommend having that but now that we know basically the simple side of coming up with the dimensions just to put it into a little bit of actual practice you know this is really what you want to have is a square this will also work but I promise you especially on larger Lumber this just doesn't work as good because it's never going to be big enough so we know that we're doing a 412 pitch right these squares have dimensions on both sides coming out from the corner and so what you can do is if you've never done a 412 pitch cut it's very simple and in the most simplest of ways you're going to put one side on four and you're going to put the other side on 12 or I can even come on to the inside and I can go for and 12 because we've also got numbers coming from the inside right once you've set this up at 4 and 12 hence the four inches of rise for one foot of run this is my triangle so I think that's pretty visible you can now make a mark and you could cut your 4 12. now what I would typically do here is I might come on down here and I might put my 4 and 12 like so just because I'm going to get more distance with a nice straight measurement and then you know you can always either take another straight edge or something if you really wanted to be precise line it up and then make a full cut or if you don't have a rafter Square you can use just a regular what I would call my framing square and you're just going to put the heel of the square against your material and you see it even says pivot and I'm going to Pivot to my common measurements this common rafter com and I want a 4 12 so I'm just going to pitch it up to the four where that lines up and boom now I have a 412 pitch okay so that's how you get this one right here this is the easy one to get it's usually a lot less steep so when you're cutting it's it's nice and easy this guy down here this is basically what we call like our I call it a reverse 412. it's basically the remainder of the 412 and I'm not going to get into all the specifics you get 90 degrees and if you split it in half you're going to get this is about 18.4 degrees 90 minus 18.4 I think it's like 71.6 so I would come up here to 71.6 this would be the other side of my triangle so I'm going to go ahead and cut one by the end of this video I will cut one and I will show you how it fits but this is for the people that are specifically wanting to build a post frame porch like we do where we use purlins this is good if you're going to do a rafter every two feet and then she's right directly on top of it we don't do that we actually build a rafter that supports basically every eight feet and then we run purlins there's a lot of reasons we do that but that's not for today's video but I am going to show you real quickly how I calculate the rest of this rafter because there is some more calculation to do so let me draw this again real quick and remember this is probably not perfectly to scale all right so we've got our beam here this is our six by six Cedar all right we've got our 2x6 fascia on this end and then this is our sheathing that's going to sit on top of it but what we're doing is we're dropping down our rafter so I'm going to have a rafter that sits just like this this is our two by twelve okay then we're going to have our purlins that go up on top of this rafter and our sheathing is applied directly to that so these are two by fours okay this is our two by twelve so hopefully this is making sense and then this is our sheathing and we do sheathing on a porch because we just want to help support snow load coming off giving the steel a little bit of extra strength now this is still a four 12 pitch so we know that we also know that this is still going to be nine feet but what we don't know is how do I get this because now if I'm measuring out to nine feet at a 412 all the way up here is three feet and all the way out here is nine feet I only want to know this to this okay so what I need to do is and once you understand triangles this is super easy so the first thing we're going to do is we're going to figure out this Dimension here so that I can subtract it from three feet that will give me the height from this point to this point so we're just going to take this little cross section okay and I'm going to draw this very quickly over here so this is my 2x4 this is my rafter this is my sheathing what we know is that a two by four is three and a half inches tall right now if I were to slide this 2x4 all the way up to this corner right here it's going to be the same this is still three and a half inches and what I'm going to do now is because I know this is three and a half I know I'm working with a 412 pitch this triangle now has shown me that this is my run this is my rise this is the diagonal and you know that because this is your 90 degree corner so it always is based off of your 90 degree corner 90 degree Corner my pitch cut I always basically consider my long measurement my run my short measurement my rise because in a 4 12 pitch it's obviously very skewed as you get to uh let's say a 12 12 now your rise and run are the exact same so we're going to take the calculator we're going to enter in three oops three and a half inch run and a four inch pitch that is going to mean that this is one and three sixteenths in my diagonal is three and 11 16. so now what I can do is back over here I now just learned that this is 3 and 11 16. I'm going to subtract that from three feet three feet minus three inch 11 16. so now this is two foot eight five sixteenths and the reason that matters is because when I put my rafter in I'm going to measure up from the top of my six by six and I'm going to set it at two foot eight and five sixteenths but I still need to know what's my diagonal how do I cut this because it's not the full nine feet well now that I learned this I don't need my nine foot because I have my 4 12 pitch and I have my rise of two eight and five sixteenths so we're gonna go two foot eight inch 5 16 rise four inch pitch that's going to give me a run of eight foot zero inch 15 16 and that is going to go right there so what that gives me now also is a diagonal of eight six and three sixteenths because like I said now that I know two of the dimensions I can get the other four so this from this point to this point is eight six three sixteenths pretty cool right math is literally when you understand it when you know the concept you can use it to figure out all these dimensions in fact I'm not going to show you because it's all the same math but I can also use the math to figure out right where this two by four goes and you might just say well just go up two feet from the end yeah that's that's fine but I need to mark it from this point here so I can use math to determine this triangle right here which basically I think is 11 and a quarter and then I can subtract 23 and a quarter so I get centered on this 2x4 from 11 a quarter from 23 and a quarter I don't remember the exact dimensions I think it's oh no sorry this is ten and a half I'm going to get 12 and three quarters the story being I can use the this trigonometry and a calculator very easily to determine all these measurements and the reason that this is super important okay I was the guy 15 years ago that just took his tape measure out and I would put it up on the roof I would have somebody hopefully hold it otherwise I'd set a nail because I was working by myself and I would go way down to the bottom where that rafter was going to end and I'd be like ah eight foot one and a quarter that is totally fine you can do that problem is a you're not going to be super accurate things aren't going to be consistent you're going to take a lot longer it's a lot harder to be accurate and the name of the game is making money now I just took all this time to do this I'm not making money right now because I'm not getting work done but in an average porch build I come to the job site these are very standard dimensions for me I can whip this out and cut all these right here at the saw horses and then go install them so it's super efficient and once you understand this guys I think it's it'll go a long way for you and even if you're not doing post frame just the concept of a right angle triangle in building and using the math to square something to get a dimension to frame something it's invaluable so I definitely recommend if this all was somewhat made sense but you're still confused just watch it again or ask questions and there's probably a lot better resources out there than what I just did this is how my brain works I don't know if it's going to be how your brain works but let's go ahead and cut one of these and we'll actually show it going up and making sense with all these numbers that we just made all right so for making my cuts on my rafter what I always like to do is make the long hard cut first because it seems like that's the most inaccurate cut to make and that once I have that point established which by the way we are talking about this long cut here once I have this point I can very easily hook it and get my Dimension measurement of my 8 6 3 16. so to make that cut I think I told you guys we can take our Square we can go 12 inches and we can go four inches like so and I can make my my mark right that's awesome my good buddy Mark and I've shared this before he made this Square he only made a couple I really wish he would make him more because I think contractors would really benefit I literally love this thing and the reason it's so valuable is because I take these little gauges slide them to a dimension I lock them in they're kind of like a stair gauge that allows you to do repetitive Cuts very easily however these ones are Next Level because they have these little I don't know they point to a number on each side so this one is pointing to six this one is pointing to 18. now if you think about it 6 to 18 is the exact same ratio as 4 to 12. basically what I did was I went 1.5 times 4 is 6 and 1.5 times 12 is 18. that way I have a 412 pitch still on this thing when I set it up but what it's doing is I'm maximizing the distance of my my framing square so I can be as accurate as possible that is why I do not use this because it's only a seven inch Mark so this thing is invaluable it will work on any pitch I could change this very easily to a 912 a 412 whatever so all I have to do is set this up it slides right on my material and I also because I like to be accurate I do grab a straight edge we're just going to grab the Stabila and I line it up on my square and that is because I want a nice straight line cut all the way through I can very easily also do this and then watch this flip it over and I can finish it on this side I don't find that to be as accurate always because Lumber has some inconsistencies and going down a two by like this if my stair gauge is not in the exact perfect like actually right here I've got a uh look at this see this little inconsistency right here if my stair gauge goes on that it now changes the pitch so I just try to stay consistent and I do one straight pitch so let's go ahead and make this cut if you don't have one of those squares you can come in here and I could set this at 71.6 degrees because that's 90 minus 18.4 which is my 412 and that's going to give me my reverse pitch but we don't have to do that everybody probably has one of these or maybe their grandpa does in his Workshop all right let's go ahead and make this cut real quick [Music] foreign so we're starting to see our rafter see that 4 12 pitch that's going to sit down on top of my ceiling framing now what we need to do is cut this top pitch this is going to go against the wall we know 8 6 3 16 from this point to this point so we're going to hook it eight six three sixteenths now we're going to grab our Square and once again this is where if we just have one of these we're going to line it up on the edge we're going to go to 412 and this is going to be our line luckily we have this nice Martinez once again and I'm just going to take it on my mark and actually well we'll just do this for now normally I wouldn't need to do this I would probably change this to a 412 it's going to shorten this up to about here and I can usually get this whole thing but for the sake of time let's just go ahead and do this okay let's go ahead and make this cut okay so now we have a rafter just like that this should go right up against my wall over here and it should sit nice and flush on the top so let's go ahead we'll put it up I'm also going to go ahead and make I'm going to make these marks this eight foot zero fifteen sixteenths and my 2 8 5 16 on the wall so that I can ensure that these are sitting right where they're supposed to go now disclaimer all of this stuff is great math never lies but when you're doing framing work with wood in humans there's always bound to be minor air now if you do your best during the framing stage of the building that you're attaching this rafter to or setting your walls that you're building a roof system on top of it should be very close but there's a good chance and I would say 95 of the time we are very close to perfect to hitting these marks but it's not exact and that's okay because the goal is always to aim for perfection and I guess settle for probably better than better than most so let's go ahead and we'll put this up all right so first thing that I'm going to do is make a Plumb line where this rafter is going to go on top of my ceiling joist here all right now what I need to do is remember that 2 8 5 16 yeah two eight five sixteenths if it's 3 16 I'll check before I go but whatever so I've got that Dimension that is where the top of my rafter should go and then I need to get my eight foot 15 16 out here at the end and that is where the point of my rafter should go come on tape measure so eight foot 15 16. what I like to do is I'm just going to set a little shingle nail here and it just helps keep my point from sliding out on me so now in theory if everything is good I can set this to that nail and that sucker will sit in perfectly you guys see my 5 16 right here see the Mark I don't know if you can see if I hit this down you'll start to see it but it's right where I want it right there so the other thing to note is on the bottom here this cut to me that really matters because not only do I want them to look good but the more that this is set in a perfect seat on top of this board the stronger it's going to be if it's only sitting on the tip and the cut is maybe at the wrong pitch it's not going to be as strong you know the problem with this oh thanks buddy the problem with this is that sometimes you saw that you saw how that may be sucked in tight we always Crown our lumber on our ceiling so there's a crown coming up in here which means that probably the middle here is a little bit higher hence why this is tight I know the math is right I know that this is good and that is now a nice seated rafter here and we will be perfect up there so now this is a simple rafter I'm set back so that when I do my purlins on top of this rafter it will plane in perfect to my fascia and that was all figured using the same exact mathematical theory that I showed you back on the saw horses so I just wanted to do a simple video I've had a lot of people request how I cut the rafters and if this was super confusing obviously drop something down below in the comments and I can try to do a better one I mean I don't have a problem doing a two hour long live video showing every minute detail but I feel like that's not for everybody it's a very small select few people and if it's really something that people would want a more in-depth but I feel like this is in depth enough to show you guys the theory that you can then use I mean to build anything I use my calculator app with rise run pitch cut to cut my Steel on the sides of my buildings to cut the roof on a hip or a um a valley we use it to frame and to check Square across the building it is literally the number one thing that I use to make sure we build as efficient and accurate as possible so I hope this helps somebody out there whether it's a a DIY first time Builder or maybe somebody who's been a seasoned Builder who just has never really known or understood the math to apply to their building and maybe this will help them do just a little bit better so with that if you guys enjoyed this at all hit the thumbs up and you know if you haven't already and you feel inclined to subscribe and make sure you're tuned in for more construction content that would be awesome too so with that I'm gonna go ahead and I'm gonna get the rest of this ports built

Channel: RR Buildings

Views: 166,281

Keywords: cut rafter, how to cut a rafter, rr buildings, how to frame a roof, how to cut a roof rafter, construction pro, learn how to, diy rafter framing, cut perfect rafters, how to cut a birdsmouth, cutting rafters for a porch, cutting rafters, using math in construction, why learn math, how to use math in construction, do it yourself, speed square, using the right tools for the job

Id: DCo66jj0dA0

Length: 25min 12sec (1512 seconds)

Published: Wed Sep 27 2023