I hesitate to throw this out there, and I’m sure substantial threads exist already, but how in the heck does a guy make sense of framing a roof for a bay window? I’ll most likely have it squared away by the end of the day, but I guarantee it won’t have been easy, and I also guarantee that it won’t fall down, but it won’t be right, either….
Thanks,…
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Replies
a 45 deg. bay is a section of an octagon , frame it accordingly
the hips bisect the bay angles... they do not run perpindicular to the house lines
a good reference is "A Roof Cutter's Secrets" by Will Holladay
Hey Mike,You summed it up real easy for him ;-)http://www.josephfusco.org
http://joes-stuff1960.blogspot.com/
thanks joe... i think you straightened me out on bays about 4 years agoMike Smith Rhode Island : Design / Build / Repair / Restore
Well....He did leave out the part where he was supposed to say, Fusco can detail it for you to seven decimal spaces...;)
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Mike,As it been that long. . . . I'm thinking about going to Pete's next year. I might actually make that one ;-)Piffin,I think Joe Carola & Joe Bartok have taken over that job! I still like to draw on plywood ;-)http://www.josephfusco.org
http://joes-stuff1960.blogspot.com/
Edited 3/27/2008 3:38 pm ET by Joe
That is how I do it - which is why you don't see me explaining my methods here...
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I can do it, but damned if I could explain how!
Well, if we are both standing shoulder to should, and I have a framing square and a piece of plywood...But that doesn't translate to text in a forum very well.
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Okay. so it is part of an octagon. I got that figured out. How would one frame an octagon "accordingly"? More specifically, the common rafters were totally easy. I got those done yesterday afternoon. the issue is how do you know where to end the hips that run along the wall? I ended mine at the same place the face ends out front. Would it be easier to make them go to where the 22.5 angle intersects the wall, and end up with a longer hip?The other problem I'm having is that the single hip rafter I have built on either side looks too low. However, the distance from the top of the window to the top of the rafter is the same on the commons as it is on the hip rafters (I did that on purpose), and everything planes out on the top. Now, the 2 5/8 that I have overhanging the framing on the commons seems too short for the hip rafter....should I just bury that all under fascia and sheathing?Thanks in advance for your reply...I'll also look for fusco's book...
<<<<<I ended mine at the same place the face ends out front. Would it be easier to make them go to where the 22.5 angle intersects the wall, and end up with a longer hip?>>>this is fairly common..... but it always looks wrong.... you should have your hips meet the wall where the bisectors of the angle fallas for overhang... this is personal preferenceif there is a soffit.... or if it's open rafters... depends on the style of the house....i like as much overhang as i can get and still make it look rightHollady's book is good as to HOW to do it.... or ...once you have the bisectors, you can do it with string lines and straight edges..... i only do then about every two years or so... so i always have to go back to the bookJoe Fusco has an excellent site as to the math & geometry of the problemdo you have a cable support system ? what is holding up the bay ?Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 3/27/2008 6:48 pm ET by MikeSmith
bay windows look odd with more 12" overhang. imop
where is joe carola he should be able to explain.
It's been 2 yrs since I've done, I agree that the way he tried to do is wrong. Odd thing is I had a GC make me reframe a bay this way "becaouse all other houses in tract had it done that way"
What a struggle to get the facia level and the soffit the same all the way around.
boy, that's true... the wrong way seems easier, until you try to trim it"you can pay me now.... or you can pay me later "Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 3/28/2008 6:39 am ET by MikeSmith
Here are some links to bay window framing math. The bay windows in question are not necessarily octagonal ...
Bay Roof Bump Out No Hips
Bay Roof to a Point Double Bumpout 45°
Bowed Baywindow Roof Framing
Web based calculators (sorry, the precision is only six decimal places) ...
SBE Builders Online Tools
Bow Window Calculator
Joe Bartok
Hi there,
You may find this article useful. 'Framing a Bay-Window Roof' by Scott Mcbride in the 'For Pros by Pros' book called 'Framing Roofs'.
Be cool to see a photo of it when done.
Cheers
Follow this thread. I posted several drawings and explanations how to frame this roof.
http://forums.taunton.com/tp-breaktime/messages?msg=87201.1
All the advice given so far is correct. Technically, you could spend a lot of time to make it perfect and the buyer might want it different.
I've built dozens of them and at some point in my career I learned to simplify the process by scaling the elevation details. If the ridge was drawn 36" above the fascia, that's what they'd get. If the width of the upper ridge was 35", that's what they'd get.
Using that theory, I'd simply nail my ridge against the wall and run it long on both ends. I'd then find center and trim each end. With that ridge defined, I'd measure for total run and total rise. This became the "pitch". I'd usually divide the totaled numbers by some divisor so I could fit the numbers onto my framing square.
I'd use the same process for the hips, as well as the commons and jacks (if any).
Total layout and thinking time: one minute to calculate all pitches. (30 seconds for the hip, and 30 seconds for the common).
Understanding the theory is a good thing to do in your home studies.
Bob's next test date: 12/10/07
Thanks again to you all for posting. All the information and links and book resources have been helpful, and I really appreciate it. Last night I decided to let the sub-fascia drive EVERYTHING. So, I installed the front sub on the common rafters, ran the ends wild, and from there I got plumb/level points for where to end the sub at the wall. This allowed me to re-define where the wall-hips ran and dictated the angle to bevel them at, and gave me a spot to make a REALLY nice rafter to split the short run of sub-fascia. It also showed me why it is so important to take the wall hips to the spot where the bisectors meet the wall....Now I'm wondering what I'm in for when I go to install the soffit. But, one thing at a time. As an carpenter I used to work with always said, "the knowledge is in the doing"...I'll post some photos when it's done. Thanks again.Steve
"Last night I decided to let the sub-fascia drive EVERYTHING."Thats an interesting statement....interesting to me because I've operated that way on every house, every overhang for that last three decades! In fact, I've never done it any other way...so it just seems natural to me. When I start a house, I usually scribble one or two key bits of information in a prominent place on the plans. For me, the most important point it the fascia line. It is my governor for everything associated with it. I derive all my other lines mathematically from this point. I qualify this fascia height with the following information: the heel (HAP) and projection. I jot this info down so I don't have to re think it on every wall. If there are multiple height fascia lines, I list them all near there locations. We then go about our business calculating the elevation of the frieze line. The frieze is the first component installed on the wall. We then add the soffit and finish it up with the subfascia and fascia. All rafter calculations and the roof plain starts at the sub fascia line.So...our bays will get their entire overhang installed before the first rafter is cut. We also use this technique for the entire roof. For me....knowing the fascia height is one of the most critical pieces of information that I need to effectively frame the house. Often, I have already calculated and double checked it in relation to our truss package before we start our first wall or finished the deck. Bob's next test date: 12/10/07
Edited 3/28/2008 9:48 pm by Jim_Allen
jim: very interesting point of view.
Have never thought of this before.
As far as installing subfacia first, that also is interesting, never done that
before on a bay window.
Heres a picture (the pictures are the same file...one is full size and the other much smaller for our dialuppers) of a "bay" that we assembled lying down on the deck. It was going to be too unwieldy to hoist so we opted to build it and tilt it. I mentioned that the first item nailed to the wall is the frieze. In this case, the frieze had to be projected out for the brick, therefore, the first components of the assembly is actually the brick rack. We will later nail the frieze onto this. All of these elements are calculated and installed from the mathematical calculations starting from the height of the fascia. It is critical for us to know exactly how far down from the top plate everything lands. In the olden days, some guys would create a story pole, much like they do with siding calcs. I've done those story poles myself in the early days of my figuring but in later years, I simply jotted down the height of the fascia, as a number and used my $4.99 dual power calculator to establish every height from there. The entire thing would look like any numerical graph using the top of the wall as the baseline. Typically, the height of the fascia would be noted as "1.625" down" or something like that. In most cases, we always wanted our window brick molds to meet the bottom of the frieze perfectly, so it was always critical to know exactly how much header we needed to get things to work out without awkward slivers of pine outside to fill gaps that might occur. Bob's next test date: 12/10/07
You realize, of course, that is a full bay, while the OP was asking about a roof on a bay window only?
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That is one of the key elements I work from with my CAD design, but somehow, I never really considered it a hands on item of importance for whatever reason.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
That sounds like a normal reaction to me too. The computers automatically are forced to assign mathematical heights to all horizontal points on a drawing, just like they do for vertical lines . When you think it all the way through from the theoretical perspective, there really isn't any other way to do it. As a builder from an area that sets their roof first, then attaches the cornice system, it's only natural that the builder would consider it of secondary, or cursory, information. In our case, since we install the overhangs before the roof, we have to know every element and make decisions to get it all to fit before we frame the first outside wall! I learned my lessons the hard way in my earliest years when I've had to reframe bearing headers because I had them installed too low and couldn't fit the cornice system to my headers. I didn't have the luxury of changing the projection because that becomes a fixed design element. Bob's next test date: 12/10/07