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You will see most everything you need to know about doing an eyebrow dormer. At least from the outside. The front arch frame is made from layered plywood, the roof rafters lay onto the roof above, and layered thin plywood is used to sheath. Look at the pics of the sheathed dormer, and not the orientation of the ply. Bend it shortways and it is easier than bending it longways. Think handrolled cigarettes when bending 4x8 sheets to a roof curve.
With an arched ceiling lookout from the living space inside, these require more framing work if the ceiling arch intersects a sloped ceiling, rather than intersecting a vertical wall. The reason is clear . . . you need a curved header at your inside end that is the shape of the intersection.
I would take a different approach I like to have a series of curved and diminishing rafters going with the curved roof. The valley boards will look like a Napoleon hat when done. The sheathing is then done down the roof not across and can be done easily without the twist and bend that is required to cross a multi curved surface. If you want to cross the roof with the sheathing find a good boat-building book and learn how to spile a plank easy but lots of work. Here is a model I used for a class on eyebrow dormers . The drawing technique is simple but requires several drawings to get all the required angles and bevels. I have used large lvls and cut out the shapes. I have also done this with a curved ceiling underneathe which will reqquire a curved valley tricky. I have a hand held bandsaw to do this so it is fairly easy but will take some time. The valley sleepers are made with 2/12 or any dimenisonal lumber that works . The two curves must be fair to each other which means that they must have the same relationship to each other. If you e mail me I will send you a drawing on how to do this
thanks for the tips folks,i have been a joiner for forty years but i have never built an eye brow roof ,they will not be dormers as such ..the eyebrows will be supported by green oak window frames that go from ground level up to the eaves .the external walls will be built from random york stone and the roof will be Westmoreland slate with diminishing courses.by the way i am from the cheshire area of england
Hey chubbs Find a book written by Manfred Euchner called Fledermausgaube. It is the best book written on eyebrows. It is written in german but if you follow the drawing system there is no need to read the text He has several ways to layout the curves and how to deminish the dormers. I spent a week following the drawings and then just had at it. You must make a one to one drawing of dormer and the main roof in section in order to get the sleeper bevels and the curved valley exact . When you draw and layout the first one it seems like magic. You must be precise however and I color code the lines such as red top and black bottom. I will scan a drawing of how to relate the curves and how to develope the valley sleeper curves and bevels. As for the book check out abebooks.com
Bob Dylan and ollee, thanks again for the eyebrow dormer photo essay and the picture of the scale model. Very informative.
I see that I'm going to have to modify my definition of the angle of the "Main Roof", or "Main Roof Pitch", to an angle of intercept between the dormer ridge and roof slope as viewed in section.
chubbs, what's a joiner? Joinery as in timber framing?
"I cannot teach anyone anything; I can only make them think." - Socrates
Here's a sketch of what I meant by modifying the definition of the Main Roof Pitch Angle. The ellipse as seen in section defines the variable pitch of the eyebrow dormer. The combination of these angles determine the miter/bevel angles for the compound angles at each end of the purlins.
Purlin intercepts Main Roof Calculator Entries
Select Pitch Angle mode
Main Roof Rise = 10.85158°
(from Section View, third image from top of page)
Dormer Rise = 19.45623°
(the Backing Angle along the Dormer Ridge Line, fourth image from top of page)
Calculator Returns Face set in Dormer Roof
Saw Blade Bevel = 67.82502°
(complementary to the 2 × Backing Angle = 22.17498°, the Dormer Plane “Pitch Angle” with respect to 5/12 Roof Plane, fifth image from top of page)
Angle on the Stick = 29.92068°
(angle between Dormer Ridge and Valley trough, second, sixth and seventh images from top of page) Sheathing Angles on Main Roof Plane
Sheathing Angle = 61.94511°
(angle between Main Ridge and Valley trough, second, sixth and seventh images from top of page)
The angles at “prow peak” and the intercept of the dormer with the level plane of the deck may be similarly tested.
Thanks again everybody,the eyebrows are a few months away and with your advice i should not have any problems.In my experience to be a roofing joiner you need to be able to picture each section of the roof in your mind before you build it. right now i am having more problems trying to get a joinery manufacturer to make a window frame out of Green Oak,the frame is sixteen feet high and about thirty feet wide and is semicircular in shape.Does any body know of any suppliers in the UK.
PS I think a joiner in the uk is a carpenter in the usa but we get called all sorts of names.........thanks
I take pictures of eyebrow dormers all the time. I'm too tired now to find all of my own photos so I thought I would post a bunch of web links from German roofing sites. Most of the eyebrows I have seen framed were done with the rib method, not the rafter type method. It all depends on the design I guess.
Thanks for the links Jeff ... they ought to keep me busy for a while.
Yeah, I caught the meaning of "Fledermaus" or "flying mouse". From German classes a looonnngg time ago, and much of the language forgotten now due to lack of practice.
Thanks for the links I have tried both methods the rafter and the rib type and found the sheathing on the rib type more economical to build . Although there is nothing economical about building one. Have you ever tried sheathing either type? I will take some pictures of both and post them.
You may want to try the french" Compagon" site they may have a link to an eyebrow. The bat wing refers to the shape of curved valley board which in one variation of the eyebrow is shaped like a napoleon hat. Manfred Euchner's book has many variations on the dormers.
No snow but lots of wind and no power for 14 hours