Tuesday, September 3, 2013

Shiften or Swanson's Blue Book

Richard Birch and I are having a discussion on Shiften. He's proclaimed for years that the best method for finding the correct lengths for hip rafters and laying out the back bevel angles, hip rafter side cut angle, was in the Swanson's Blue Book that you get when you purchase their SpeedSquare. So, I went out into my garage yesterday and found the Swanson's Blue Book that came with the last Swanson's Speed® Square I purchased.

Shiften = Transfer the dimension in plan view to elevation view.
Shiften = Transfer the dimension in plan view to profile view.
elevation view = profile view

After studying the Shiften - Shiftungen roof framing geometric layout techniques I see no difference in the layout techniques between the Swanson's Blue Book and Shiften.  They never mention the word shift or shiften in the Swanson's Blue Book, but it's the same technique that's been used by the French and German carpenters for centuries.

I'm actually impressed with the Swanson's Blue Book for describing this technique no matter what it's called.

I just thumbed thru "A Roof Cutter's Secrets", by Will Holladay, and even thou Will Holladay does not use the word shiften he still uses the same technique as shiften for the location of the second plumb line on the side of the hip and jack rafter.

We've all used the second plumb line on the side of the rafters with the dimension taken from plan view and drawn each of the views separately, but by combining the the two drawings it's called  the Shiftungen layout technique like the drawing above.

Richard and my discussion on the Swanson Blue Book


Swanson's has evolved. This is a much better explanation than the earlier versions.

Their diagrams still only refers to the Hip length applied at the outside shoulder. Fig. 11 & 13

The "Explanation of Shortening of the Hip" (p.23) is new. This is the stuff I recognized from the meager instructions of my older version. And as I remember, their earlier versions were better than the one I have too. They (cheap bastards) obviously have had some user feedback. (or maybe they read my online posts from years back?) For myself, this method is still the best, as I gather from other books or articles, on the same subject. Less confusion once you get it.

This book is still my top pick for recommended reading. The geometric principles laid out in their regular Hip explanation work for every roof I have encountered. There are additional considerations when applying it too Valleys and Broken Hip Rafters. You just need to visualize the shoulder lines breaking the plane of the effective Ridge height. (This is the real secret to understanding the side-cuts/length applications! *No Ridge, then project thru the total Height) *(rotated rafters too? Footprint geometry at Ridge plane? useful?)

*Additional Considerations;

1) Valleys are essentially upside down Hips, Cheek bevels reverse directions. (I will drop the unbacked Valley to plane away from the shoulder but short of center. An even reveal for tighter sheathing cuts. )

2) The Irregular Broken Hip rafter may need extra considerations for calculating the length, depending on the relative directions of the two ridges. If they are parallel, [Effective Run = (difference in spans /2) - ridge thickness]. If the ridges are perpendicular, then the hypothetical parallel ridge is (plan-view ratio) proportionate to the lower Ridge. Depending on which is Major or Minor, the ridge thickness deduction affected. (It will be > r/t or < r/t, but not equal to lower r/t)

*On my Hips, Reg/Irreg, I mark the Hap plumb lines on both sides of the Heel to make setting it on the corner precise. When both lines are aligned with their wall line, that's where they go. No footprint layout needed.

*yes, thicker lumber will need modified approaches. I calc the bevel short points at each shoulder, and cut to the center.

I hope you have found this exchange of information beneficial, as I have. I have taken this Swanson's concept to new levels, far beyond where they leave off. (but they're getting better.) And this is why I post the stuff I do. The H/V- drop/shift issue is not a dead horse, it's a simple-stuff Thoroughbred. =) (as concepts go . . . . )


Text from the Swanson's website
Speed Squard
Includes markings for Swanson's® One-Number Method™ of rafter layout, and is packaged with the Swanson® Blue Book of Rafter Length and Roof Construction. 

One-Number Method™ of rafter layout

So what does that statement mean?
of determining the angular pitch of a roof 

Swanson® History
The Swanson® Speed® Square and the One-Number Method™ of determining the angular pitch of a roof were first developed in 1925 by a carpenter named Albert J. Swanson. As his fellow tradesmen began to appreciate the ingenuity of his idea, they wanted their own Speed® Squares. Swanson began to hand-make the squares to fill requests for the tool. Demand for the work-saving tool continued to grow, and in 1930 the Swanson® Speed® Square was first sold in interstate commerce. By 1945, Swanson started Swanson® Tool Company, Inc., to manufacture and sell the Swanson® Speed® Square through recognized channels of distribution. His son, Ronald C. Swanson, assumed control of the company in 1971 and added other quality tools to the line.


I was reviewing the page scans you posted and I got confused by the 1/4" line spaced at the ridge. (( Line A,A)   Figs. 11 and 14)  (not in my book?  missing text?)

If Figs. 14 and 15 are overlaid, there is a discrepancy.  See below.

After editing I realized:  The discrepancy is . . . not a discrepancy.  They are showing the Hip length to the center of the Ridge.  Sort of unnecessarily confuses the illustrated explanation.  I have overlaid the effective rafter length lines (plan-view).  The plane of the effective ridge height is "greeted" by the Hip at the perpendicular red "head-cut" line location.

Maybe this is not very important. (above)

One thing that is important;  Swanson's "Shiften" method shifts the effective H/V Rafter line length(s) to the shoulders of the H/V Rafters.  Performing the cuts with a modern circular saw effectively shifts them back to "Center".  Therefore, to process the H/V rafters, all that is necessary to do is to mark the length on the shoulder, mark the plumb lines *(w/Hap @ Heel),  Perform saw cuts, w/bevels, and/or Heel clearance, as required. 

Once you get it, it's like cracking the code, Snap!  Simple Stuff!


I was interested in that ¼” as well. They show it 2 times. One for the center line of the ridge meeting the hip in plan view. The book also said mark off a line about ¼” long of the plumb cut line and cut on that line.  The width of the teeth of the saw blade?

Richard Birch's method,One Length Method that he developed from the Swansons Blue Book. Measure from the plumb line shifted at the foot of the hip rafter using the hip rafter length to ridge dimension, 29 1/4", to the long point of the hip rafter. Then use the Adjacent Plan Angle as the Saw Blade Bevel Angle to cut along the long point of the hip rafter plumb line shifted forward .

One Length Method© Richard Birch


  1. Sim,

    Our exchange was respectful and polite. I enjoyed it. Thanks


  2. The "One Number Method" refers to the unit pitch number. One Number, two scales, Common and H/V.

  3. Sim,

    It's their method, you'd think they'd know how to explain it better! I like it though, keeps the stuff I write from infringing on any copyrights. Lol =)

  4. The Swanson® Speed® Square was first developed in 1925 by carpenter Albert J. Swanson. It would be fun to find the original Blue Book that came with the Swanson® Speed® Square in 1925.

    The current Swanson® Little Blue Book describes using a circular saw set to 45°. In 1925 I doubt 1 in 100 carpenters had a circular saw. I think the price of a circular saw was about $100.00 in the 1930's. Pretty pricey for a carpenter that only made about $100.00 a month's in wages.

  5. Sim,

    The last illustration you posted is spot on! Looks Familiar too. =)

    Geometry is Geometry. It is the approach that I have that is different. Simplifies things big time!

    The Modern Circular saw just makes it that much easier.