How to build an Octagon Roof

hey guys have you ever built one of these today we're going to show you how to build an octagon roof now a lot of people look at these and think they're very difficult to frame but actually any regular polygon is fairly simple so what is a polygon it simply means an enclosed figure and a regular polygon is an enclosed figure with equal sides now the easy way to build these is with roof framer's Bible I wrote this book some years ago and it's loaded with information on how to frame practically any kind of roof and I put a link in the description below so you'll know where to get one now for roof framing the two most common polygons are hexagon and octagon now roof framer's Bible includes charts for five different regular polygons Pentagon which is a five side hexagon which is six sides an octagon like we're going to do today with eight sides a decagon 10 sides a do deagon 12 sides today we're going to use it to show you how to build an octagon and we want to start by going to the drawing on page 204 of rof framer's Bible okay here we have the drawing on page 204 and also combined with it the Octagon chart from page 209 just like a circle every polygon has 360° total all the way around it so to get the angle of any particular side we simply take the 360° and we divide it by the number of sides now this is an octagon so it has eight sides so 360 divided by 8 gives you 45° on each of these corners now half of that is going to be the working angle 22 1/ 12° and you'll see that down at the bottom of the chart over here for each of these polygons it will give you the working Angle now the two most important elements when working with an octagon is the common rafter run that's from the outside to the center here and the length of side and if you look at the top of our chart it says common rafter run time 828 equals the length of the side and inversely if we already have the length of side we can divide by 828 and that will give us our common rafter run so quick and easy to switch from one to the other now the great thing about this chart here and all the polygon charts in rof framer Bible is that it uses factors and that's basically a one number method so whatever value you have you can multiply by a single number or factor and get the value that you need quick and easy and you don't have to do a big long string of mathematical calculations with a bunch of trigonometry you simply take what you have multiply it by the one number factor and it will give you the value that you need so here in the chart we've got all the information we need to frame any octagon from a 312 all the way up to a 312 okay let's take a look at some of these factors often times you will need to know the run of the hip Raptor so that's from the outside corner here back to the center that's the horizontal run of the hip rtor and we can quickly get that by going the bottom of our chart here and it says common rafter run times 1.82 will give us the run of the hip rafter and we see that right here now we also have the pitch of the hip rafter now Carpenters know that on a regular rectangular type hip roof the pitch of the hip will always be the pitch over 17 so if you were doing 812 pitch the hip pitch would be an 8817 now on an octagon roof this is all standardized across all octans the pitch of the hip Raptor would instead be the roof pitch over 12 and 78 so if you had an 812 roof the hip pitch would be 8 12 and 78 now in the model that we're going to build today we're doing a 1412 and that's highlighted here on our chart so our hip pitch would be a 14 over 12 and 78 for the hit pitch now this drawing for the book is for a different size and Pitch than the model we're building today so to illustrate what we're doing for the model it's a 1412 pitch so let's take a look at how we get our rafter lengths for the model today so to get our common rafter length we simply go here to this 1412 line and we multiply our common rafter run which in our model is 18 in times 1.53 7 and that will give us our common rafter length in the same fashion to get our hip rafter length we use this hip length Factor right here we take our common run of 18 in times 1.59 one and that gives us our hip rafter length for the model today now here lastly in this right hand column it gives us the sheeting Cuts it's 12 and 7/8 and that's from the long to short point on a 4 bit sheet of plywood so you can see that this one chart quickly get you all the information you need your your Raptor length your hip length your hip run your sheating Cuts everything you need very quickly for any Octan from any pitch of 312 to 312 super quick and easy all right here on our model we've got an octagon that is 36 in wide so from here to here 36 in and of course it'll be the same top to bottom as well so to start framing this we need to get the length of our side and we know from the top of the page on ref framer Bible that we use the common rafter run to get that so half of our overall width we had 36 in so half is 18 in that would be our common rafter run and we simply take that 18 in and we multiply it by the factor that's at the top of our Octan page 828 and that will give us 14 and 78 of an inch as the length of our side so every side is 14 and 7/8 in Long all the way around exactly the same so it's really pretty easy so all we've got to do is cut eight pieces 14 and 78 in long with a 22 1/2 Dee angle on each end now as we talked about an octagon has 360 degrees for the whole we divide that by the number of sides this is an eight-sided octagon that will give us 45° so this angle here is 45° all the way around half of that will be our working angle of 222° so cut eight pieces that length and that miter and we assemble them in a circle Arrangement and we've got our octagon super easy okay the Octagon is assembled and we've got these joints at each point and having them all the same makes it easy to assemble these and properly align them but this is weak you've got a joint here at Each corner so you always want to reinforce that with a top plate so you want to lap a top plate on here and run it long so that overlaps the piece on either side so that when you nail it it locks of these Corners together to make a strong roof typical use of a top plate so that completes our top plate we're ready to set some Rafters all right we need to layout for our common rafters and we're going to have uh eight common rafters there'll be one in the center of each side of the Octagon so since our length of side was 14 and 78 of an inch that means that the center of that common will be seven and seven 76 to the center so we want to go 3/4 each way that's the layout Mark for our common rafter and we'll just repeat the same thing all the way around the roof well now we're ready to set some Rafters but we got a decision to make you see one of the most complicated elements of these octagon roofs is the center point we've got so many things coming together in the center it gets a little crowded up there there's more than one way to do this and we're going to take a look at a couple of them okay here's the first way of going about doing this this is a plan view drawing of our octagon that's looking down straight from above and we want to look at how these Rafters will come together in the center right here so if we look at it closer we've got a common rafter on this side and a common rafter on this side and we'll allow them to butt straight in the middle now the common rafters on the top here and the bottom will deduct 3/4 of an inch from each of them so they can butt into the side now the four remaining common rafter that's here here here and here will have a double cheek cut on them so that they fit up into the corners of these other common rafters now all of the hip Raptors there'll be eight of those they will have to have these sharp cheek cuts on each side and each of these hip rafter shown in yellow will be have to be put all the way around right up in between the common Afters so that's one way of doing it as you can see it gets really crowded up here in the center of the octagon and uh there is an alternative way of doing that we'll show you in just a second okay here we have the same plan VI drawing showing the second way of doing this so as we zoom up here closer you'll see that we have this blue octagon that's around here and this is representing our Ridge pin and so each side of the Octan will be an inch and a half wide so this common rafter can butt to this face this common rafter here can butt to this face and so forth and so on all the way around and that makes it a little easier than having quite so many of these competing Rafters right up here in the center now a way to do this which we're going to use today is to have for a ridge a little mini octagon and that way we've got an inch and a half flat spot all the way around for each common Raptor to butt against it as you can see here now if you remember before we used the common rafter run to get the length of the side of our larger Octan in this case we know the length of side is going to be an inch and a half the width of our common rafters so if we use the factor in Reverse we take the inch and a half divided by 828 and that will give us the common rafter run of our little mini octagon here so if we double that it will give us three and 5/8 in across the whole thing so that tells us what we need in order to make a deductions from our common rafter so quick and easy to set this up there and have each common rafter but these inch and a half wide facets here at the ridge okay if we want to lay out our rafter we need to know our adjusted run so that would be the 18 in which is half of our overall octagon minus the 1.81 in that half of our little octagon Ridge that will give us an adjusted common rafter run of 16.19% overall rafter length of 24.8 in and that would be along the top of our rafter here from this point down to the hap right above the plate and there's our common rafter I'm not going to go into how you lay out these Tails or how to position a square on the rafter for that you want to go to our first video a beginner's guide to roof framing so we just go ahead and cut these and we position all the common rafters right around the roof [Applause] so that's all of our common rafters and now we're ready to set some hip Rafters now the hip Rafters are longer because they run on an angle the common rafters are Square from the plate but the hip runs on an angle which means it it has to run longer now if you're doing a larger Octan and you need to calculate the run of the hip Raptor that's very easily done you simply go to the bottom of the octogan chart and it's got a factor you take the common rafter run times 1.82 and that will give you the horizontal run of the hip rafter from here back to there the same point as the common and that works for any pitch regardless as long as it's an octagon that factor will work to get your hip rafter run now because that hip is running longer than the common rafter it changes the pitch just like you have on a regular hip roof where the hip rafter will be uh whatever the roof pitch over 17 instead of 12 it's the same thing here on octagon so the hip pitch will be a little flatter than the common Raptor pitch it's going to be whatever the pitch is over 12 and 78 so so that's true regardless of any pitch if it's a 142 like we're doing here that uh hip pitch would be a 14 12 and 7/8 whereas the common rafter would be a 14 over 12 now to get the length of this hip rafter we go back to our chart and we take the common rafter run times the factor the the hip length factor of 1.5 91 and that will give us the overall length of our hip rafter so we cut our rafter and we' got some really sharp angles here on the top you see the way it sets up in the corner you know and that's really too sharp for you to cut with a skill saw but if you'll cut this Square on a plum cut of the 14 12 and 7/8 and then scribe a line right down the middle set your saw in 22 and2 de and cut it this way setting on that square end and you can cut that 22 and 1/2 this way yields this much sharper angle viewed from the side and that gives you the angle that you need need to jam right up there between them now on the bottom end of your little hip you need a double cheek cut of 22 1/2 deges on each side here at the end of your overhang that's so your fascia can run out here in a line now you also will need to put backing bevels on the top of the hip or as we did here drop the hip so the shoulders of the hip will flush out with the commons on each side we cut the bird's mouth here an extra 38 of an inch to allow it to drop down to plain these roofs out so we'll just set all these hip Rafters so there you have it pretty cool little octogan roof the only thing left is to put the roof sheathing on roof framer Bible makes that really easy too you just go to the same chart and over on the right side of the chart it gives all the sheathing cut so for the 1412 pitch we see our sheathing cut is 12 and 7/8 that's from long to short on a 4bit sheet but it gives the roof sheeting cuts for all the roof pitches from 312 to 312 see polygons are really pretty easy because they're standardized it's the same angles all the way around all the rafters are exactly the same length not bad pretty easy to do roof framer Bible is is a great book loaded with all kinds of information on how to frame practically any kind of roof it has all the rafter lengths and angles All pre-calculated For You in a compact pocket reference that you'll want to have in your nail bag or in your truck but there isn't space for an expansive explanation of every roof framing situation for that I want to recommend this companion book a roof cutter Secrets by Will holiday it is fantastic it gives detailed information on all kinds of framing situations will was a master Carpenter he built in the tracks doing production houses for many years and then he went into Custom Homes where he encountered just about any kind of framing situation that you can think of and he have detailed all of those in this great book including chapter 10 the expansive explanations of towers and polygons such as we did today you really want to get a copy of a roof cutter Secrets I put a link in the description below to be sure you know where to get one you don't want to miss out on this great book I hope you guys enjoyed this video and you want to hit that subscribe button so you don't miss out on our coming videos and to see all of our current videos please check out our playlist right here thanks for watching guys and we'll see you the next time

Channel: RoofFramersBible

Views: 9,117

Keywords: Octagon roof, octagon, polygon, gazebo, bay window, bay window roof, rafters, roof framing, carpenters, framing, framing square, speed square, jack rafters, hip rafter

Id: cxYmL5xp_MU

Length: 17min 28sec (1048 seconds)

Published: Thu Feb 15 2024