*
I’ll try again……
I will be building a room off the main house that is octagon shaped. The measurement across the new room from outside of wall to outside of wall is 11′ 6″. The exterior walls will go out from the main house wall at 90* for 6′ 6″ before we make the first 45* angle. The wall (after the start of the angle) is 4′ 4 13/16″ before it hits the next 45* angle. That wall runs parallel to the main house wall for 4′ 4 13/16″ to another 45* angle, then goes another 4′ 4 13/16″ to another 45* angle, then back 6′ 6″ into the main wall of the house.
We will be using trusses with a 6/12 pitch across the 11′ 6″ way out to where the first 45* angle starts. Then we would like to somehow stop the gable type roof and switch to a hip roof (with 4 hips). I’m not sure how to accomplish this. And I’m not sure where to stop the gable part and tie the hip part in so that the soffit and fascia all line up.
Can anybody offer some help? Is this enough information?
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Replies
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check my response in const techniques. It may be what your looking for.
jim
*jim is a very good source, see his post. Also JLC and FHB have both done articles on framing octogons and bump out bays which will give yo some help.
*Ray,I'd like to give you some help, but I just can't seem to understand your post. I'm attaching a drawing to this post showing what I think you are trying to describe. But notice that neither of the dimensions add up to 11' 6" as you claim. So either I didn't draw it correctly, or you need to tweak your math.I'll let you look my diagram over and comment on it before going any further.Ken
*Nice drawing Ken, however most octagon roofs have a run of 13 instead of 12. so where you listed 6/12 it should be 6/13 but the person framing the roof should calculate the run first to make sure it is correct. I purchased the Advanced roof framing videos from Peters building videos and he covered a section of a roof exactly like the one in this post, well worth the money. His web site is http://www.roofbuilding.com
*b.loc, The hip itself runs on a 6/13. The rest of the roof is 6/12.
*So another words, the hip would run at 6/17 off of a 90 degree corner, and 6/13 off from a 45 degree corner FOR a 6/12 roof. It's just the hips themselves and nothing else.Billy
*AllysonThanks for clearing that up i left that out
*b. loc,The topic of octagon roof framing seems to appear in Breaktime, as well as other topics like crown molding, about every 2 weeks. I've explained the relationship between the common rafters and the hip rafters probably a couple of dozen times over the past 2 years. If you do a search for both octagon roof framing as well as framing other types of polygons ( hexagons, decagons, dodecagons,...), you'll find a tremendous amount of information on the subject.I've saved some of my drawings from previous posts. I'll repost one of them for both Ray and yourself to look over, as well as any other interested posters.Ken
*Here's another one that I've posted in the past.The first column shows the number of sides of a regular polygon. If you are using a framing square to cut the hips, instead of using 12 on the blade of the framing square, as you would for cutting common rafters, use the number in column 2 instead.So for a regular octagon( 8 sides), if the commons are cut at 6/12, then in column 2, you see to cut the hips at 6/13.If the polygon had 10 equal sides( a regular decagon), and the roof pitch were 6/12, you would cut the hips at 6 / 12 5/8Ken
*Mr Drake,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe,I suppose that's a possibility. Maybe Ray will get back and clear this up for us.Ken
*Thank you all so much for the responses!!I am so sorry I haven't responded back to your questions promptly. I have been out of state to a funeral and am still trying to catch up. I will answer all your questions tonight.Ray
*Ray T Have you thought of putting this question to a truss supplier. If he's any good he should be able to build everything you need as well as tell you where to put them.jim
*Ken,I must have read my math book wrong! This is how I came up with the measurements --- I was told that to find the length of one side of an octagon, you take the sine of one half the angle (45*) times the diameter of the octagon. So...the sine of 22.5* x 11'6" (the diameter). That is 0.3827 x 11'6" = 4'4 13/16". That is how I got the octagon side length. Maybe I misunderstood the formula. The constants in this project are: 1) the outside to outside measurement of the new room is 11'6", and 2) the first 45* angle starts at 6'6" from the house.
*Honestly....no I hadn't thought of that. Good idea. But you know, I would really like to learn how to to figure it out the right way, too.
*Ray,Welcome back.I'm attaching a diagram to help you understand the mathematics of an octagon. Each interior angle of an octagon contains 135º. If you draw a line from the center of the octagon, to any vertex, it divides the angle into 2 equal angles, each containing 67 1/2º, as shown. This leaves 22 1/2º for the other angle of the triangle that is not the right angle.We know that the span of the octagon is 11' 6" = 138"Therefore, half the span = 69". So, if we use the tangent function, and let "x" = 1/2 the length of a side of the octagon, we find that x = 28.58". Therefore, the length of a side would be 2x=57.16", or a little less that 4' 9 3/16"In general then, for ANY regular octagon, the length of a side = tan 22 1/2º times the span.or, .4142 x span = .4142(138")=57.16"
*RayT,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Ray,Once the walls are built and braced, it's a piece of cake locating where the last truss should go. Just take 1/2 the length of a side of the octagon, and mark it off from the corner as shown in the diagram below. Put the CENTER of the truss on that mark (assuming the truss is 1 1/2" wide)
*what does "inscribed octagon " mean?
*Ray,Do you have a reason for wanting to frame this little addition using BOTH trusses and conventional roof framing? If so, fine, but why not just frame the whole thing with rafters 16" on center? It's quite easy, and I'll be glad to help you out.Ken
*Ken, Just out of curiosity, what would happen if you moved the last truss forward all the way to the first 45* angle and let the hips fall short of coming to a point? I just wonder what that would look like.Ray
*Ken,No actually, I probably won't use trusses. But I thought it might be easier to explain that way. I would much rather frame the whole thing the way you described.Ray
*Ray,I wouldn't recommend moving the last truss or rafter out to the corner as you mentioned. If you do, you end up cutting down the run of the common rafters out on the end sections, forcing the roof pitches to become steeper and unequal. See diagram below.The section of roof out on the end would have a new roof pitch = 10 1/4 / 12 and the 2 side sections would have a pitch of 8 1/2 / 12. The last truss, or rafter, actually turns into an irregular hip, and the other two hips become irregular also. This in turn causes the overhangs, (which are not shown) to be unequal for each section of the roof. There are several other problems that you will face but perhaps I've already convinced you not to go this route.Ken
*Ray,I've got to work 1/2 a day tomorrow, but later tomorrow, and on the weekend, I'll spend some more time with you on this, if you'd like. Right now, I need some sleep.There are also others who post here that may have alternative suggestions for you.Talk again tomorrow.Ken
*Yeah, Ken...I don't want problems with the fascia lining up. Although, I was trying to describe making the hips go to a point only in theory, but in reality, cutting them short and making them run into a "gable end" formed by the last truss or rafter (which would have to be moved forward to make that happen). Maybe that's too complicated and I should just leave the last truss or rafter where you suggested. Good night! Unfortunately, I have to work all day tomorrow to get caught back up.Thanks for your help. I'll check back tomorrow evening. Ray
*RayT,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe,That's a good way to show the relationship of a side of the octagon to the span of the octagon. Let me restate the rule, and repost the diagram "cleaned up" a little.GENERAL RULE: To find the length of a side of a regular octagon ( all sides equal ), multiply the SPAN of the octagon by .4142If s = a side of the octagon,then s = .4142 x SPAN
*Mr Drake,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe,I'm not sure what you are talking about.Here are my exact words from my post #16:"In general then, for ANY regular octagon, the length of a side = tan 22 1/2º times the span. or, .4142 x span = .4142(138")=57.16" That's exactly what I said in post # 28.So what exactly is it that you claim you are clearing up for me?
*Mr Drake,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe,I never used the words Inscribed or Circumscribed in any of my posts. Those words imply that a circle is involved in the discussion. There is absolutely no need to bring that approach into the picture.I said that the length of a side of a regular octagon is equal to .4142 times the SPAN of the octagon. I'm using the word SPAN in the same way we use it in roof framing discussions. The measurement from outside wall to outside wall of 2 parallel walls of the octagon, the same manner in which you would use the word in framing a gable roof.What would you consider the Span of an octagon to be, the diagonal measurement?
*Mr Drake,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe, In your previous message you stated, and I quote: "as the diameter of the circumscribed circle, making his walls (sides) to short. He did this by using the sine function." I think you should have used the word "too" as in "too short" rather than "to" which you did. - Peter
*Would I have the same unequal hip problem and non-matching fascia if I made the hips go to a point only in theory, but in reality, cut them short and made them run into a "gable end" formed by the last truss or rafter (which would have to be moved forward to make that happen)?Ray
*Ray,I've read your last post a few times. Is this what you mean?
*pm....to is too in Joes posts...Ya got to know the lingo of each around here....not to(o) far from da stream,ajAnd as ya all can see...Joe and Ken speak there own math yak to(o)!!!Great graphics you two...
*Jack,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Boy...I can sure see an old thread topic coming back to haunt!!!!!!!near the twelve ways to skin a cat or turn a turret...ajor cut a porch corner...or build a bay roof...or half an octagon or two thirds of a palatypus..
*Mr Drake,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Snow!>?Where...When...I got the skiis ready to rip!near the stream looking up,ajWe have 5" fresh from last night.
*Jack,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe...Would you build it the way you said to build the porch a few tense threads ago?near the stream,ajJust checked the price on a returned snowblower at Lowes...13hp $1600 regular...repaired..clearance at $900. Only thing is it is wicked heavy.
*My way too!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!?????????????????Pullin up the weather.com site....The stream gonna get plowed under,oh..and I was out watching my nephews play hockey in there end of the year Gazilla tournament...Also stayed to watch Glens Falls Indians hand a downstate team their butts back!...Our man scored four goals in a row...What a hat trick!
*Joe...You are in the track...I am above the heavy snow it looks...nearer to the 6" of snow over the stream,aj
*Oh well...I might get lucky if it turns North!would love to be stuck on the slopes under 3'...andunable to get back to the stream,aj
*Ray,If you find my last post, I showed a roof plan of what I think you were talking about in post 35. Here's what it would look like (roughly) from the front. Is this the look you want?
*Jack,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Jack,
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Yes, Ken. I was hoping to be able to do something like that rather than a regular octagon hip. Ray
*Ray,It's a little unusual to frame it that way out on the end of an octagon, but I see no reason why you can't, if that's what you'd like to do. The way I have it drawn, with all roof surfaces = 6/12, the fascia would have the same overhang on all sides. By the way, How much overhang do you want on this little addition, and will the fascia be plumb, or square to the rafter tails? In other words, will you have a flat soffit, or a 6/12 sloped soffit? Normally, you do what exists on the main house.Also, will the walls be 2 x 4 or 2 x 6?Ken
*Ken,The reason I wanted to frame it that way is because the main roof is a gable roof and there are a couple of gable dormers, and the room with the octagon end would be the only hip style roof on the house. I thought it might just help tie the addition into the rest of the house. But tell me if you think it would look wierd, because I don't know for sure. Seems like I have seen it framed that way before and it looked OK, but I have driven all over the country lately looking for one and can't seem to find one now!The rafter tails on the main house were cut at 16 1/2" with a 2x4 for subfacia, making an 18" soffit. The tails were cut plumb, so the fascia is plumb and the soffit level. The exterior walls are 6".Another question now arises.....would an 18" soffit look too large on the little gable end that the octagon hips rest against? Maybe I should cut that soffit back to 12" or something? What do you think of this whole idea? You don't have to be nice -- just tell me.Ray
*Ray,Let me start by letting you know that the telephone company technicians came by this morning and completely screwed up the phone lines on this street, so I won't be posting much today. They're supposed to fix things tomorrow morning, so be patient. When are you scheduled to frame the roof?In the meantime, let me comment on your last post.I frame roofs for a living Ray, and I must say that I don't recall ever having framed an octagon end in the manner that we have discussed. I'm not saying that it will look bad, just that its unusual to do it that way. It's sort of like a Dutch Octagon Hip, if you will. It boils down to a matter of choice, and that choice is yours.Either way, it's a fairly easy roof to frame, and I'll be glad to help you with it.As far as the overhang goes, typically when small dormers appear on a roof, or small additions are added to a house, the architect often will show less overhang on these little structures so that the large overhang doesn't overwhelm the little frames. Since the fascia won't tie into any other fascia on the house, the final appearance might be more pleasing to the eye if you cut down the overhang to about 12", as you mentioned.I have to get off line for awhile to free up the phone, but in the meantime, I'll let you take a look at a roof plan that I drew up if you decide to chooses "Option A" with the hips running all the way to the ridge. I want to stress something. This is only one way to frame the roof. There are a variety of other ways to cut the individual rafters to get the same result. But notice that the hip rafters are all exactly the same length, and are cut the same way, except for the fact that the short point of the 22 1/2º bevel at the top is on opposite sides for 2 of the hips.Any bevels that occur on the header blocks are also 22 1/2º. The little 4 1/4" blocks that occur at the top of the hips are beveled at 45º. So you don't have to make ANY bevels beyond 45º using this method.
*Ray,There's one thing that may be a problem with "Option B", where the hips terminate against the gable end.When you put the fascia on the gable end, at the top, it will look like any other gable end. But what will it look like at the bottom end of the fascia? There's nothing to let it die into at the bottom end.Also, depending how much overhang you gave it, you might have to make a long tapered cut on it which wouldn't look very good.Try to imagine what I'm talking about, and see if you have a solution that would make the fascia look good.
*Thank you Ken. I know that this sort of stuff takes time, and I appreciate the fact that you are so willing to help. I would have this thing ALL screwed up! I would even have built the foundation wrong, because I used the wrong formula to determine the octagon side lengths. Then the walls would have been wrong, etc. all the way to the roof. Then I would have wondered why the roof angles didn't work right. Again, thanks!And Joe taught me about inscribed and circumscribed circles. Never had any idea.....Thanks to Joe also.I will start construction on the room the first part of April, so I have some time yet. I may go ahead and frame it like you drew in "option A" (maybe), but I am not the only one involved in that decision, so we may still want to do the "Dutch Octagon" style.(probably).I look forward to your posts.Ray
*Ray sent me this picture and I just wanted to share it. It's a great rendering!
View Image © 1999-2001"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe,I'm glad you posted it. Ray sent me the same "shot" to look at. I was going to ask him to post it but you took care of that.Maybe you have a suggestion for him as to how he can make the fascia look as good as it appears in the rendering, if he frames it similar to that.I've already described my thoughts to him. Since he doesn't have the valley to return the fascia to, I'm concerned about how he can finish it out and have it look good. It seems to me that he would have to rip a small piece of fascia from zero to whatever, to finish it out How would you do it?Anyone else have any ideas for Ray??
*I think Ray started out with intentions of a carousel roof, and has now made it into a (almost) dutch gable. To me the fascia dying out into the soffit like that will look like a mistake, no matter what you do. Make it a dutch and the fascia will sit neatly on the front slope. Just my opinion, since you're asking.
*Mike,That could be right. How would I go about making it sit neatly on the front slope?Ray
*Ray,I think what Mike is suggesting is that you let the fascia that is on the front parallel wall extend out in both directions until it meets the fascia from the 2 sides ( extended ) at square corners.Then you just put in 2 regular 6/17 hips and create a true Dutch Hip roof. I'll draw it for you later.Mike,If I'm misinterpreting what you're saying, please correct me.
*Ken,I'm not sure I would like that because it leaves a huge soffit at the corners. If I'm thinking what you're thinking.....it would be a 90* fascia & soffit even though the walls cut across at a 45* ?? I would rather have the fascia/soffit follow the walls.Ray
*Lots of goofy roof lines in the last twenty years...I have seen this new fandangled stuff so much that it is normal for todays tract homes...I like the lines of the old Victorians much better but for some reason they are not being built anymore.the times are a always a changing...near the stream in three feet of heavenly perfect powder...skiing till someone cries uncle..and I don't want to here it!aj
*Ray,I don't think it's a good option either, but maybe Mike was thinking of something different.If it was what he was thinking, I'd suggest going with Option A instead, for a much cleaner look. I don't like that huge soffit look on the sides either, but it's a matter of personal choice.I suppose you could consider framing the addition as a rectangle and then putting a Dutch Hip on it, but it's probably to late for that.
*Ken,You understood perfectly. It would create large soffit corners, but this approach is more "common" than the other method Ray has in mind. Like you said, it's all personal preference. Usually when a dutch hip is used on a bay like this the 45's are 2' corners (34" long). The large soffit corners aren't nearly as big as they would be on Ray's roof.
*Mike,That's just what I was thinking. More often than not, that front parallel wall is longer than the 2 side 45º walls anyway, at least down here.Ray,Take a look at the diagram I'm attaching that shows what Mike is describing. If you cut down the lengths of the 2 45º side walls, the soffit decreases with it. Looks a lot better, and the area of the gable end that shows increases as the hips are shorter. Just something else to think about Ray
*Ken,I agree, that would make the soffit smaller and not so objectionable. However, that would leave only 2' 10" or so across the diagonal wall and we would like to be able to put a 30" window in those angled walls. I'm really sorry. I'm sure it seems like I'm finding fault with every suggestion you folks make. But I haven't decided which way I'll end up framing it yet. I just have to let you understand why we were wanting it the other way. I guess we could always put smaller windows in the angled walls, and maybe 2 small windows in the wall parallel to the house. Still thinkin'....Ray
*Ray,I took one of my earlier drawings that I posted here and added the gable fascia. Now it looks like the Cad rendering that you sent Joe and I and which Joe posted earlier I believe in post #56You'd have to make the overhang at the gable end large enough so that the gable fascia clears the octagon fascia. Then you'll basically end up with what you saw in the rendering.What would you do about the area I've got marked with a question mark? Box it in with more soffit? Or leave it open?Something to chew on....Ken
*Ken,If I didn't make the gable overhang that big would the gable fascia just have to be angle cut to sit just above the octagon hip roof? It appears in your drawing that the gable overhang must be 2' or more to be able to clear the octagon fascia. I can see though, that if it wasn't done that way that the fascia wouldn't appear as in the rendering. Hmmmmm, still thinkin'......Ray
*Ray,It's just a sketch. You probably could make it work if the overhang was about 21" beyond the gable end, but I didn't work out the math.But look at it this way. The gable fascia is on a 6/12 pitch. So in 16" of run, it would rise 8". The plumb cut on a 2x8 ( 7 1/4") fascia board is about 8 1/8".So, if you go 16" beyond the point where the outside of the octagon fascia meets the inside of the level side fascia extended , you should clear by about 1/2",( the top of the gable fascia board is 3/4" above the outside edge of the level fascia at the inside corner where the gable fascia meets the level extended side fascia)But there's still the problem of the double soffit to deal with. You'll already have a soffit inside the octagon fascia. Now you'll have a second soffit running down the gable end. Won't that soffit land on top of the octagon roof as you move back towards the gable end? And then when you got by the octagon fascia, how would the soffit finish out in that little triangular section that I marked with a question mark?Chew chew chew
*
I'll try again......
I will be building a room off the main house that is octagon shaped. The measurement across the new room from outside of wall to outside of wall is 11' 6". The exterior walls will go out from the main house wall at 90* for 6' 6" before we make the first 45* angle. The wall (after the start of the angle) is 4' 4 13/16" before it hits the next 45* angle. That wall runs parallel to the main house wall for 4' 4 13/16" to another 45* angle, then goes another 4' 4 13/16" to another 45* angle, then back 6' 6" into the main wall of the house.
We will be using trusses with a 6/12 pitch across the 11' 6" way out to where the first 45* angle starts. Then we would like to somehow stop the gable type roof and switch to a hip roof (with 4 hips). I'm not sure how to accomplish this. And I'm not sure where to stop the gable part and tie the hip part in so that the soffit and fascia all line up.
Can anybody offer some help? Is this enough information?