Saturday, March 29, 2014

Les Haras Strasbourg

Patrick Moore, Le Canadien 'L'Ami du Trait', the first North and South American Compagnon Passant Charpentier. , helped with the restoration of the Les Haras Strasbourg, horse stud farm in France, and shared some pictures of the restoration. The roof framing  design is intriguing with the rotated purlin plates and the purlin wind braces.  As I was going thru the pictures of the roof framing I decided to draw out some of the roof framing design to see if there was something that I didn't understand about the roof framing. It's an overlay roof  with the purlin rafters supporting the roof rafters. The roof design didn't present anything that I didn't understand geometrically, except for the horizontal joist with the notch for the purlin plates where the hip rafter is located.

Patrick Moore's Historical Carpentry Website

The first time I dimensioned the angle at this location I thought I had the wrong angular dimension. However, after using the trigonometric formula for rotating vertical planes the angular dimension is correct. This is a new angle for me. The notch in the common rafter joist is the angle of the roof slope, 33.69007° in these drawings. Rotating the vertical plane by 45°, or the plan angle results in a vertical plane angle of 43.31386°. This would have been drawn out using traditional layout geometry by the French carpenters and they wouldn't have cared what the actual angle was. As long as the geometry was correct. However, this angle is not present in the Timber Framing Angles.

Maybe, we could call it R8?

Seat cut layout on horizontal timber for purlin rafter following the hip rafter run line.

Timber Framing List of Angles

arctan(tan(33.69007°) ÷ cos(45.00°) = 43.31386°

Geometric development for the notch in the hip rafter run line joist.

Joist with notch for Purlin Plates.

Purlin Plates installed.
The typical purlin rafter angles.

Added some jack rafters with a claw to position the hip rafter.

The rotated purlin wind braces can be drawn out on the roof surface using the fold down or draw down layout technique.

The overlay rafters in position. 

While your at Patrick's website be sure to watch the restoration of the Les Haras Strasbourg videos. Here's a screenshot of some pretty big crown-gutter molding. I wonder if they have any eave to rake cut miters on this building? Look at the end grain of the crown-gutter molding. It doesn't get any better than this for 250 year old timbers.

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