Saturday, September 22, 2012

Saillies De Toit

I thought this might be a good book.

La CHARPENTE en bois de Gilbert Emery ( RELI - 1 avril 2005)

I draw out page 148, .Saillies De Toit.

Roof projections
With regular projection,  = equal overhang

The ground plan is a trapezoidal ground plan with equal overhang. The book does not explain how to calculate the hip offset from the corner of the ground plan. Disappointing!!!
Back to the drawing board to see how to draw or calculate the hip offset for roof eave angles that are not at 90° and have unequal roof slope angles.

This drawing was generated by my Google SketchUp plugin using the Trapezoidal Ground Plan function.

Irregular Hip Rafter Ground Plan With Equal Overhang
It easy to draw out the tetrahedrons at the hip overhang when the roof eave angle is 90°.
It's also, just a simple math equation to find the hip offset from the corner of the fascia line.
Major Pitch Overhang Run / tan(minor plan angle) = Offset Run on fascia line
24 ÷ tan(36.8699) = 32

Here's a drawing with the math for the trapezoidal ground plan with equal overhang to find the hip rafter offset from the corner of the building plate line.


  1. Sim ,
    Draw a line tangent to the hip run , then measure along the tangent line from the center the thickness of your hip . From that point draw line parallel
    to the opposite eave into the eave, this point becomes the side of the shifted hip . This works with any plan angle . In all the Mazerolle drawings if you look carefully you can see this operation . I will look for that book next week while I am in the Compagnon book store in Paris . Try drawing that on the scan I sent you last week very simple

  2. Billy,

    I'm not sure if we're taking about the same hip rafter offset. I uploaded another drawing of the trapezoidal ground plan with equal overhang with the hip rafter backing offset drawn in. I was dissapointed in the book not explaing how to draw out the hip rafter offset from the eave line -- ground plan corner.


  3. Sim ,
    Nice next step is to use the drawing of the backing to give a view or the hip in section looking either up or down showing the view of the shifted hip with the differing backings

  4. Sim, Now I see what you are talking about . I have rarely seen it explained it is only drawn . In one of my Manfred Euchner books written in French ,there is a very good example of the offset .However the book is not with me ,I have lent it out to someone and I will not get it back for a few weeks . To late to scan for this conservation