Saturday, January 2, 2016

Divers Hip Rafter Boucher

This method of drawing out the divers hip rafter was shown to me by Olivier Phojo. He said the French compagnon-Professor J.D. Boucher (1890?), developed it. This method of drawing out the diverse hip rafter using the Sauterlle method, bevel square, is brilliant. Boucher may have developed the method, but Olivier drew it out were I could easily understand it. I looked through Boucher's book , L'art Du Trait of Charpente, yesterday and I couldn't find this method in his book.


This method of drawing out the bevel square angles for the divers hip rafter only takes a couple of minutes. 5 minutes at most. It's something Billy and I should teach in our roof framing geometry classes.  






Start off by drawing 2 perpendicular lines. You can draw this on a piece of paper 24" x 18". Then place the framing square on the vertical line and the end point of the framing square on the horizontal line. Trace the framing square for the profile rafter roof slope angle. In this task model I use and 8:12 pitch (33.69007°).


Next draw a perpendicular line to the roof slope line. This line will represent the eave line. I used 12" in this task model for an equal pitched roof. Then connect the eave line to the rise of the roof slope triangle. This line will represent the hip rafter on the roof surface.


At the intersection of the hip rafter on the roof surface with the horizontal line draw a perpendicular line equal in length to the roof slope triangle's tangent. 6 21/32", or 6 11/16" in this task model.


Then draw the diverse hip rafter bevel square lines connecting back to the roof surface triangle.




The red angle is used for the miter angle on the side of the diverse hip rafter. The blue angle is the top bevel on the diverse hip rafter.

The orange angle is used for the miter angle on the side of the diverse hip rafter and the blue angle is used for the bevel angle on top of the divers hip rafter for the first face cut at the head of the divers hip rafter. For the second face cut use the brown angle on top of the diverse hip rafter and the miter angle on the side of the hip rafter will be 90°.




Another drawing using a different roof slope angle. The DP line is easier to understand in this drawing. You don't need to draw the DP line, but you can check your cuts with the DP line.













Here's a picture of laying out the miter and bevel angle on the foot of the hip rafter using the red and blue angles. The cut will be a parallelogram, so you use the same angles on the top and bottom of the foot cut.





Here's a picture of the layout for first face cut at the head of the rafter.


Bottom view of the rafter layout.




The cut at the foot of the hip rafter is complete and the first face cut is complete.



Checking to make sure the foot cut aligns wit the eave line and DP line in elevation view.



Checking to make sure the first face cut is plumb to the horizontal plane.



For the second face cut you use the brown angle or 90° to the first bevel cut on top of the rafter.


Second face cut laid out.













I checked the accuracy of my drawing using a digital bevel square.




I then used a skill saw for all of the cuts. You could align the blade for the saw blade bevel angles on the timber, but using some math makes somewhat easier.

For the divers hip rafter foot cut I used.
Miter Angle 27.1°
Saw Blade Bevel Angle  = arctan(sin(27.1) ÷ tan(50.24) = 20.7 °

For the divers hip rafter face cut #1  I used.
Miter Angle 49.07°
Saw Blade Bevel Angle  = arctan(sin(49.07) ÷ tan(50.24) = 32.1 °


For the divers hip rafter face cut #2  I used.
Miter Angle 90°
Saw Blade Bevel Angle  = 39.7 °

Here's a link to a PDF file that you can print out for this task model layout.
Boucher 8:12 Pitch





Here's a wire frame drawing of the Boucher technique. Your folding the canted plane flat to the plumb plane of the hip rafter. I'm guessing you can use this same technique for just about any canted rafter.



Another example of folding the purlin rafter (frieze block, bird's block) plane flat. Pretty easy, only 3 triangles.






9 comments:

  1. Sim,


    I always find your roof framing models interesting, but I often miss the rationale.

    If each hip roof surface is framed independently, and had rotated hips, and the eaves were square to the pitch, plus eliminate the Birds-mouths (foot cuts), then all the face angles of the framing members will be square (90*)and all the bevels will be sheathing angles.

    This is how lightweight steel framing was done, using computer driven roll-form machines, back 16 years ago when I took classes to learn how to use this new technology that was developed in New Zealand. *(Exception being that No Bevels were required with Lightweight Steel since the channels overlapped. System used computer punched holes with stainless steel pop rivets and screws for fasteners.)

    Even though this technology was new and exciting back in the year 2000, In the end I felt the technology was still in its formative years and I could not justify the personal expense of the pioneering required to iron out all the bugs to complete this light-duty innovative residential framing process. All the affordable and available tools and materials in the USA are geared for Wood Framing.

    Other than for this, what is the purpose for rotating Hips square to the sheathing? Are there any examples of Hip roofs having been framed like this? Are they doubled up?

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  2. Richard, here's an example of rafters with no birds mouth and some sprocket rafters.
    https://picasaweb.google.com/104523684702206530180/DumasResidenceWoodside#5407502590136792754

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  3. For the rational of the roof framing I'm studying.
    For the most part, the United States roof framing carpenters are third rate and I want to change that. The European carpenters are building roofs using techniques that are centuries old that we should have known in our prime. Like I've said before I've cut and stacked somewhere between 5,000 and 10,000 roofs. Half of them were truss roofs with continental stacking and the rest were full cut and stack. I thought I was pretty good at roof framing until I saw what the European carpenters were building. The Canadian carpenters have classes being taught by Patrick Moore on complex roof framing techniques that are centuries old. In his class he covers the four different types of hip rafters. The four different type of hip rafters are, the waled, slatted, furring, and diverse. So, yeah I wanted to study the diverse hip rafter as well. I have an 11,000 sqft house I'm framing and I want to try to add the diverse hip rafters to the house. However, the diverse hip rafters will have rafter tails. Something else I need to study.

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    Replies
    1. I am 100% with you on this Sim. North American carpenters are a laughing stock in comparison to the Europeans. I'm with you Sim in that I want to change that!! I want North American carpenters to be the best in the world. I truly believe that we can and we want to without even knowing it. I've been dedicating my life to this art form known as Art du Trait. Throughout all my time studying in various universities, colleges, and private institutions across North America, I've never came across this knowledge until I went to France and studied it intensively for years with the Compagnons. Recently I've been dedicating myself to the creation of the School of Practical Stereotomy, like the C:. Pierre Francois Guillon.

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  4. I've studied with Patrick and found it fascinating and am working my way though your equally enlightening blog.
    As for the rationale behind diverse hips; cutting long backing angles on the top of rafters prior to electric saw would have been very time consuming. Far less shop time involved in rotating the hip into one of the roof planes. This leaves one set of jack rafters very easy to cut, and one side more difficult, but if you can determine the necessary alignment, plumb and birdsmouth angles and locations, it is still less work than ripping the back of the hip by hand. An added bonus could be that the hip member can be slightly smaller, as the necessary structural depth is achieved along the diagonal of the member. But I am no engineeer.
    More importantly, everyone I show a diverse hip to is intrigued by it, which gets them interested in hiring me.

    Sean

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    Replies
    1. Sean, yeah I agree with everything you said about the diverse hip rafter. Most of the carpenters today don't know what it's like to frame a roof without using a circular saw. The first circular saws came out about 1930. At $125.00 , that was more than the carpenters made in a month. So all the hip rafters that were edge beveled prior to the 1930 were edge beveled with a draw knife and hand plane. With the diverse hip rafters, no edge bevel was needed. I have a hard time edge beveling my small task models. I couldn't imagine edge beveling a 30' hip rafter. Chappell has a picture of a diverse hip rafter in one of his books. He said the jack rafters were spiked, instead of mortised.

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  5. Sim,
    This method is known as 'Herse de Pente' and the Compagnon Joseph Denis Boucher developed it in 1837 when he was only 21 years old. C:. J.D. Boucher became the chief architect for the town of Buenos Aires, Argentina, and the urbanist of Mentevideo, Uruguay. He studied under the world famous C:. Pierre Francois Guillon. You can find an entire article dedicated to Pierre here ---> http://www.historicalcarpentry.com/pierre-francois-guillon.html

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    Replies
    1. Thanks for the info on Boucher Patrick. I added a wire frame drawing to this page. I'm not sure if it makes any sense, but I might call this technique of Boucher's, the "folding flat" technique. Your taking a canted plane and folding it flat against a plumb plane. Then drawing it on a 2D plane. I haven't checked it yet, but I'm guessing this technique can be used for any canted plane.

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    2. There are a couple 'folding flat' techniques. The most common method is known as the 'Net method', that is literally folding any plane flat on the neutral plane to be able to view it from 90 degrees. This other method 'Herse de Pente' directly translate into 'Net Pitch'. Both of which are different and have advantages and disadvantages. There are a many different methods of drawing to solve any problem. Each method has its pros and cons and acts like a tool in your tool box. The carpenter will use a specific method based on what is needed to be accomplished. That being said, you wont use a very complex method for a simple problem, nor would you use a simple method for a complex problem. Although you can still use one method to solve any problem, but it can take a lot longer and can be less accurate. It's nice having the knowledge of many methods because you can pick and choose what method best suits the problem.

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