Andrew Fischer of BuildZoom Master Series class Pictures

Here's some more pictures taken by Andrew Fischer of BuildZoom at their  Master Series class on traditional roof framing geometry.

Ancient Knowledge Tour of Roof Framing Geometry Class

BuildZoom Master Series class on traditional roof framing geometry was taught by Billy Dillon and Sim Ayers at BuildZoom's office in San Francisco California. This class on Traditional roof framing geometry , Art Du Trait - Schiftung, is the geometrical knowledge and techniques used for drawing out complex cuts of solid objects, on 2 dimensional planes on paper or wood drawing boards. It's a simplified technique developed from the ancient art of stereotomy. You can use trigonometry to layout a lot of compound joinery, but transferring lines from a drawing board makes makes a lot of the  compound joinery quite simple.

One of the questions that came up before the class began was, what books to buy on traditional roof framing geometry for carpenters wanting to learn Art Du Trait - Schiftung, that's in English. Our answer, none. It's definitely something that needs to be addressed. There's plenty of advanced books in French and German on this subject, but there are no books written in English that explain the theories of laying down the lines on paper for developing complex cuts on a 2 dimensional plane for beginners.

Billy and I decided the easiest way to teach  someone traditional roof framing geometry was to start with the roof framing kernel. It's not the geometrical drawing technique used for  Art Du Trait - Schiftung, but it's an easy way for American carpenters to comprehend the laying down of planes in a one day class. The main difference between the  roof framing kernel and Art Du Trait - Schiftung, is that the roof framing kernel does not use a depth or width for the profile rafters. 

Billy drawing out the geometry for the roof framing kernel. With the roof framing kernel you can use the grasshopper method, bevel square, to transfer angles from the drawing to the timber.

The roof framing kernel folded out  with the real roof surfaces developed and the technique used to draw out the hip rafter backing angle. Everyone in class draw out the kernel and then cut and folded the roof framing kernel drawing to have a better understanding of folding planes.

Everyone trying to draw out the hip rafter backing angle as well. I was quite impressed with some of the student drawings. I checked Tim's hip rafter backing angle on his drawing and it was right on the money.








Billy drawing out the geometry for Dachausmittlung, Geometric Roof Design, roof averaging. This drawing technique is used to locate the hip run lines on complex roofs that don't have eave lines meeting at a 90°.

After lunch Billy draw out some of the geometry for the eyebrow roof dormer. 

Billy explaining the direction of the edge bevel of the elliptical valley rafter to Brian Copper.

After lunch I explained the hip rafter plumb line shift for the edge bevel on the hip rafter. Developed from the intersection of the level plane line and the hip rafter plumb line shift.  Jason Smith then used his draw knife   and hand plane to edge bevel the hip rafter in this picture. 

We moved on pretty fast after lunch. We were all pretty much burnt out from the morning geometry session .  Or at least I was. The morning session went really well for the amount of information that the students were presented with.  After explaining how to draw out the TE (top edge) and BE (bottom edge) of the rafters on the fold down roof surface, I had all of the students lay a block of wood on the folded down roof surface drawing board and transfer the miter and bevel lines to the purlin rafters. In this picture Greg is cutting his purlin rafter with Jason and Eric installing the purlin rafter Eric cut, with Scott looking on.

Tucker transferring the lines on the fold down roof surface to the purlin rafter with Scott cutting his purlin rafter.

Here's a picture of Jason at my house on Friday transferring the lines from the fold down roof surface to the purlin rafter.

Everyone in the class cut a purlin rafter from the fold down roof surface drawing. Jason and Eric cut the timbers for the Saint Andrews cross on the right side of this Octagonal  task model.

Many thanks to Andrew Fischer at BuildZoom for putting the Master Series class together.

Off Angle California Valley Framing

Off Angle California Valley Rafters can be calculated using one of my RafterTools+ apps.

On this house the main roof slope is an 4:12 pitch and the off angle California framing is at an 6:12 pitch. First enter 4:12 for both the Main and Adjacent Roof Pitches, with an Eave Angle of 90°. The calculated results will give you the Main Roof Hip Rafter Slope Angle = 13.26268° and the  Main Roof Hip Rafter Back Angle = 12.92097°. 

To calculate the California Jack Rafter Foot Miter Angle and Saw Blade Bevel  Angle for the Off Angle California Valley Framing  can be accomplished by entering an Eave Angle of 45°, Main Roof Slope Angle = 18.43495° (4:12) and Adjacent Roof Slope Angle = 26.56505° (6:12)

Roof Eave Angle = 45°

Main Roof Slope Angle = 18.43495° (4:12)

California Valley Roof Slope Angle = 26.56505° (6:12)

Main Roof Hip Rafter Slope Angle = 13.26268°

Main Roof Hip Rafter Back Angle = 12.92097°

With the RafterTools+  calculated results you get an 

Valley Sleeper Saw Blade Bevel Angle = 48.46304°

For the Jack Rafter Foot  Miter Angle you add the California Valley Roof Slope + Main Roof Hip Rafter Slope Angle.

Jack Rafter Foot  Miter Angle = California Valley Roof Slope + Main Roof Hip Rafter Slope Angle

Jack Rafter Foot Miter Angle = 26.56505 + 13.26268 = 39.82775°

For the Saw Blade Bevel Angle used on the Jack Rafter Foot Cut

Saw Blade Bevel Angle at Jack Rafter Foot Miter Cut = Main Roof Hip Rafter Backing Angle

Saw Blade Bevel Angle at Jack Rafter Foot Miter Cut = 12.92097°

 The  RafterTools+ has the California Jack Rafter Length Difference  or use the following Trigonometry formulas.

Roof Sheathing Angle = arctan(sin(Jack Rafter Foot  Miter Angle) ÷ tan(Main Roof Hip Rafter Back Angle)

Roof Sheathing Angle = arctan(sin(39.82775) ÷ tan(12.92097) = 70.29288°

California Jack Rafter Length Difference = O.C. Spacing ÷ tan(Roof Sheathing Angle)

California Jack Rafter Length Difference = 24” ÷ tan(70.29288) = 8 5/8"

The Valley Sleeper Miter Angle is not built into the RafterTools+ apps. You can use the following formula for the miter angle at the foot of the Valley Sleeper.

Valley Sleeper Miter Angle = arccos( cos(Sheathing Angle Angle) × cos(Jack Rafter Miter Angle at Foot))

Valley Sleeper Miter Angle = arccos( cos(70.29286°) × cos(39.82772°)) = 74.99102°

With a Valley Sleeper Saw Blade Bevel Angle of 48.46304°, you can use this formula for the snap line dimension on the Valley Sleeper for the edge bevel.

Edge bevel width = Valley Sleeper Thickness / tan(Valley Sleeper Saw Blade Bevel Angle)
1.69323 = 1.5 x tan(48.46304°)
or 1 11/16" = 1.5 x tan(48.46304°)

Set the saw bevel angle to 48.46304° for the Valley Sleeper edge bevel.

After you have edge beveled the valley sleeper you can use the Valley Sleeper Miter Angle (74.99102°) for the Valley Sleeper foot cut.

This porch has trusses and I aligned the valley sleeper with the edge of the truss for the location of the valley sleeper.

The ridge cut has a 4:17 miter angle to set on top of the main roof valley rafter. I scribed the miter angle for the valley sleepers at the peak. 

For the Off Angle California Valley Jack Rafters I laid out the 6:12 level cut, then used the 39.82 angle for the Jack Rafter Foot Miter Angle.

For the Off Angle California Valley Jack Rafters length difference I used the 8 5/8"  from the RafterTools+app.

The extra blocks at the ridge are for a CS14 strap that runs the full length of the roof. The second row of blocks are for plywood sheathing edge nailing.