How To Calculate, Layout And Cut Jack Rafters For Hip Roof Framing Without Difficult Math Formulas

in this video i will show you how to cut the jack rafters or the fill rafters and these are going to be the raptors that connect to the hip and for those of you who are looking for more information about figuring out the hip and common rafters i will put links to those videos that i have already made in the video description box and cutting the jack rafters isn't going to be much different than cutting the common rafters you're going to use the same seat cut and angle as you did on the common rafter so here i just took a few extra common roof rafters and just kind of extended them to provide you with an idea of how everything is going to connect together and one of those examples will be that the seat cuts on the raptors will be the same the only difference between the two is that the jack rafters will be incrementally smaller than the common rafters and instead of a square cut they will have a 45 degree angle cut on them but i thought this might help i know sometimes a few pictures can really make a difference and since i can throw as many as i want into these videos then why not do it so here we have the 45 degree angle cut on the jack rafters along with the measuring lines that you're going to be using after you figure out the spacing for each jack raptor and in our case we are going to be spacing them 24 inches on center and then measuring and marking them accordingly to that layout pattern and what i usually do is measure from the corner of the top wall framing to the top of the angle cut on the jack rafter and i also refer to this point as the long point and often we'll write lp here so that i don't forget what side of the roof rafter i need to cut when laying it out and i'll explain more about that here in a little bit now another thing you might want to do if this rafter is not nice and straight will be to install some type of a support brace to make sure that you can straighten it out and that it will not be moving because you're going to use this rafter to measure the location of the rafters where they will intersect into the hip and that can simply be done by hooking the tape measure over the common rafter and then measuring 24 inches making a mark and then working your way down until you have marked each one of the jack rafter locations at the top so that you'll know exactly what to measure and where that point will be intersecting into the hip and of course if the hip roof rafter is not straight then you will need to install a brace and of course both the hip and the common rafter will need to be perfectly straight before you do any measuring or layout next up let's go ahead and take a look at the top point where you will be measuring from and again i have the jack rafters in here we're just trying to give you an idea of why or where you're going to be measuring so let's go ahead and remove the jack rafter so that we can have a more realistic situation of what you're going to be dealing with and you can see here where the measurement is 8 foot 7 and 3 16 to the long point of the rafter and to the other side of the framing plate and now let's take a look at the layout here two foot on center and let's go ahead and zoom in here so we are going to be hooking over the right side of the rafter and then marking the raptor location on the framing plate and i would also recommend placing some type of a symbol like an x or just even a line that can be used as a reference point so that you attach the framing rafter on the correct side of the line and i know that sounds like something i'm not going to make that mistake well then my advice to you would be to mark it anyway and here is a close-up of where you're going to be measuring each point two so that you can figure out how long the jack rafter is going to be and now that we have the measurement we need let's go ahead and lay out one of the jack rafters and even though you won't be doing this i'm going to use two common raptors in our example along with the jack raptor that we are going to be laying out however you will not need to use a common rafter all you will need to start with will be a piece of lumber with the measurement for the roof overhang along with the seat cut and you will not need any type of cut on this end because you're going to be laying that out for each individual jack rafter next let's take a look at how i have the seat cut on this rafter facing in this direction and the seat cut in this rafter and this one facing in this direction and this is another thing you're going to need to figure out before you lay out the rafter because all of the rafters that will be going on the right side of the hip will have a long point and a 45 degree cut like this and all of the jack rafters that are going to be going on the left side of the hip in our example will be laid out with the seat cut facing in this direction and if this doesn't make sense it will make sense to you when you cut your first rafter a little short if you don't have it laid out in the right direction and the reason why i'm pointing this out is because i've made this mistake myself before so again we're going to be starting with a seat cut and an overhang measurement and then we're going to be laying out the same angle that we used on our common rafter at the top that's the same that's going to be on the jack rafter and here you can see where we have a square cut on the common roof rafter and a 45 degree angle on the jack rafter and by now you should have a pretty good idea what the jack rafter is going to look like when it's finished so let's go ahead and lay one out with our line that is going to go from the edge of the seat cut corner here all the way to the long point on our rafter so let's go ahead and make sure that we're all on the same page here that line to this line now for those of you who might be having a difficult time figuring out how you're going to get this or the fact that you could be off a quarter of an inch a half inch or an inch if it's not done right however you should be able to get an accurate measurement if you start by hooking to the corner of the seat cut and then pulling the tape tight or in a straight line until the measurement you're looking for lines up with the top of the board or the edge of the board here and this might require you to have somebody else hold the other end of the tape measure and if you're off a quarter of an inch or a half inch it might not be a big deal however that's going to depend upon all of the measurements you took and how accurate everything is that you're working with next up let's go ahead and place the framing square and since our rafter pitch is a 4 and 12 ratio we're going to line up one side of the framing square with the 4 inch mark and the other side with the 12 inch mark as shown here and don't forget that your measurement might be different and you'll have to change the ratio to match the roof pitch you're working with then mark the line that you need that you're going to cut at a 45 degree angle and make sure that you are going to cut that angle in the right direction and that might require you to put an lp or some type of a reference for the long point and even an arrow maybe pointing to the corner so that you don't cut it in the wrong direction now this won't be a big deal if you cut it in the wrong direction for example you have the 45 degree angle running this way because you're going to be able to re-cut it in the right direction without wasting very much lumber however if you make the mistake and cut the rafter a little short you'll just simply use that for your next rafter or in some cases see if it will work for the rafter on the other side of the hip and to cut the rest of the rafter simply repeat the method that i just provided you with to finish cutting the raptors on this side and of course the measurements from this side should match to this side and to the jack raptors or fill raptors that you're going to use on the other side for example these rafters here will work for this side as well as the rafters that are going to be here should work fine for this side and of course you can double check all of these measurements as you're cutting cut a rafter install the rafter double check it cut the next rafter double check the measurements for that if you're off a little bit then you should be able to make minor adjustments along the way because the last thing you want to do is cut three more jack rafters with the same measurement and of course if all of that makes sense then my job is done and by now you have a pretty good idea on how you can cut your jack or fill rafters without using any complicated math formulas you

Channel: gregvancom

Views: 26,492

Keywords: how to, calculate, figure, length, layout, cut, jack rafters, roof framing, construction math, methods, measuring, installing, carpentry, do it yourself, learning

Id: UbGTW8d7-mA

Length: 10min 4sec (604 seconds)

Published: Sat May 08 2021