When someone says "framing square," we all probably think of the same object. But before it became a mass-produced tool in early 19th century America–and the tool we all think of–medieval European timber framers used framing squares to lay out bents and ribbed vaults for houses and cathedrals. It didn't originate with them either, though, because Roman carpenters used framing squares to build hip roofs and formidable warships. And before that, wooden squares dating back to 1500 B.C. have been found buried ceremoniously in the tombs of master Egyptian builders.

The framing square is as simple in design as it gets, yet its markings point to uses far more complex than its obvious appearance implies.

So what? you might be saying, a tool that does more than one thing. And really, who cares? In this era of computers, calculators, digital tools, and laser-guided layout, why bother learning this dead-language tool when instant answers to complex problems are just a button-push away? I can give you the answer in one word: Foundation.

The Keys to the Kingdom

I'll always remember the first tool kit I assembled as an apprentice carpenter and the old, well-seasoned carpenter who told me to buy it. He instructed me to show up with a 16-foot-long 3/4-inch-wide tape, 2-foot spirit level, 1-inch chisel, 22-ounce Plumb hammer, 10-point Disston handsaw, and that shiny L-shaped piece of steel–the framing square. Like the other apprentices, I thought the wormdrive and pneumatic nailer I soon acquired were the keys to the kingdom and I used my square mostly for marking wide boards and square-checking corners. Little did I know (or care) of the language this tool really spoke; I ignored the markings and scales until I started framing roofs myself.

It was only when I needed to learn the language of the framing square that I began to really pay attention to the square–and discovered what learning it really meant to me, my craft, and my bottom line.

To increase my roof-framing skill, I read books, used rafter tables and got handy with a speed-square. But after all that, it was the framing square that gave me the best and clearest window into the world of roof framing, where you need trigonometry and the understanding of compound angles to conceive, in 3-D, intersecting roof planes when there is only space before you. And, using the framing square really got me to believe in an important concept I eventually read in the 1923 book How to Use the Steel Square by Frank Graham: "The intelligent workman should not be satisfied with knowing which number to use but he should want to know why each particular number is used."

Basic Training

Just like a foundation supports a house, knowledge supports your trade. Understand the principles of basic construction and you will increase your current skill level; you will support an understanding for what you're currently building–and what you have yet to build.

I didn't really grasp the elements, the building blocks of roof-framing principles, until I spent some serious time with the framing square. It wasn't that I used it to figure out rafter lengths or lay out the rafter cuts; I used–and still use–a calculator and a speed-square, unparalleled for their speed and accuracy. My time spent with the framing square–and the true understanding of the geometry behind how to lay out rafters and rooms–was inspired by a section in A.F.J. Riechers' book Cuts for Steel Square. Practicing his examples in the book opened my eyes to the fact that I had missed an entire step in the learning process, which is the ingredient necessary for true understanding. It isn't easy to fully tame the framing square–truly a calculator in its own right–and it's a tool that supposes a good working knowledge of arithmetic and geometry. In the late 19th and early 20th centuries that wasn't a big concern, but today it's another story. That doesn't mean, however, that the knowledge–or the need for it–is extinct. On the contrary, to take your skill set and business to the next level, you have to understand the source code underlying all the modern calculators, rafter tables, and specialized tools you probably already use on site. It's the difference between reading a menu and understanding the ingredients of a recipe.

Learning the four basics detailed below unlocked what a framing square could do for me, and they will help you and your crew brush up on their dead-language skills.

Seeing Is Believing

The gift of using a framing square as a calculator, like carpenters did from 1500 B.C. until the middle of the 20th century, is that it gives you the ability to "see" in your mind's eye what you're building. To actually transfer the angles, pitches, and intersecting planes of commons, hips, and jacks found on a 2-D plane on plans into a picture of what it will look like in 3-D takes time at first, but that investment more than offsets any temporary slow-downs in production you may experience while scratching your head the first couple of times.

Exercise 1. Stepping-Off Full-Length Rafters.

As an apprentice, I thought this was a ridiculous method to use in laying out rafters–especially with instant access to a rafter table book and a tape measure. I eventually tried it and fooled around with the exercise in Riechers' book. While doing the steps detailed in that book and others, I grasped the concept of rise, run, and building span, with a clarity that no rafter table or calculator could possibly explain better.

Simply place the square on the rafter stock at a determined pitch and step the square up the rafter at each 12-inch increment of the building run (see "Exercise 1" illustration, page 66). This simple, repetitive action establishes a clear, visible connection to the function of rise and run. Doing this exercise demonstrates the principle of proper measurement and layout and its relation to the workpiece, a concept that is often misunderstood by beginners. Follow up this method by doing it with a calculator and a speed-square and it'll drive home the point and sense of learning from the foundation upward.

Exercise 2. Stepping-Off the Hip Rafter and Marking the Plumb Cut (Head Cut).

No other part of roof framing can befuddle a beginning carpenter more than laying out the standard hip rafter. But once it's clearly understood, a clear path is laid for tackling irregulars and bay roofs.

The hip roof is the intersection of three triangles, as opposed to the two triangles that make a gable roof (see "Exercise 2" illustration, page 72). Laying out a hip rafter with the framing square requires the square to be set on a unit run of 17 inches (16.96 inches rounded off to 17) instead of the 12-inch run used for commons. Seventeen inches is used because that's the unit length of any diagonal on a square whose sides are 12 inches (see top left corner, "Exercise 2"). As the process of stepping-off a hip is done, the carpenter is reinforcing the diagonal-to-square relationship, and this paves the way for other layout know-how. For example, the same method used to step-off a hip rafter can be used to lay out a 45-degree bay wall pop-out.

If the bay wall protrudes from the building line 2 feet, you can strike the bay angle line because now you know its length has to be two times the diagonal of a 12-inch square or 34 inches, (33-15/16-inches precisely). Learning the hip in this manner will open up the door to understanding irregular hips, roof designs requiring the diagonal of the hip to be other than square.

Exercise 3. Jack Rafter Side Cut.

One of the fun things about using the framing square is discovering hidden elements of framing, particularly a jack rafter side (or cheek) cut. The plumb cut on a jack is the same as the common but the jack must also bevel to sit snug to the valley or hip rafter. On a standard hip, the jack rafter comes from the plate at a 45-degree angle toward the hip. To make this bevel cut on the jack's plumb (or head) cut, you set your circ saw on a 45-degree bevel and cut through the plumb mark. This leaves an appropriately beveled side cut that can be nailed tight against the hip that fits perfectly. The interesting thing is that the bevel isn't really 45 degrees–and this is important to know because the first time you have to cut a beam roof, one that is beyond the capacity of a circ saw, you'll need to lay out a side-cut bevel greater than 45 degrees to get a snug fit. (Note: The true angle varies with each pitch, increasing in degree as the pitch gets steeper.)

The best way to understand this is to use the framing square to lay out the jack side cut. One way is to use the jack side cut setting found in a rafter table book, or if you are lucky to have a square with rafter tables stamped on it, look up the square settings on the tool itself. However, this number makes little sense unless you inquire about its origin.

The side cut is derived from the diagonal per foot of run of the common/jack. To really visualize this, lay out the side cut in the manner shown in the "Exercise 3" diagram on page 74. Once done you can see that the length of diagonal per increment of run creates the bevel angle. This really shows up elsewhere, too–when you're cutting plywood to cover a hip or valley. The angle needed to make the plywood sheathing fit is the same angle as that of the jack rafter side cut bevel.

Because I know this from the layout exercise, I can lay out and cut plywood sheathing to fit precisely along a hip or valley rafter. I use a calculator to do this on site, but it was the framing square that taught me how to make the calculator figure out the dimensions needed to do it on a full size piece of plywood. That insight has saved me time and made me money.

Exercise 4. Backing a Hip Rafter.

The framing square got its name during the Middle Ages when timber framers ruled the guilds. Back then the square was as powerful a tool to the skilled tradesman as a fully loaded laptop computer is to today's structural engineer.

It's not uncommon to run into a framed roof built with large-sized lumber, whether it's for strength, looks, or both. Roof framing with 4-by, 6-by, or 8-by has its own particular challenges and one of them is "backing" hips. Backing refers to a bevel or chamfer cut on the top edge of the rafter so plywood will lay snug to the beam (see "Exercise 4" illustration, above). In normal 2-by framing, backing isn't much of an issue as the hip is dropped at the seat cut in order to allow the sheathing to plane over the top edge; however, this can't be done with timbers and a carpenter must bevel-cut the top edge of the rafter beam so the sheathing can plane over the top.

Using a square to lay out a standard hip gives a carpenter practice for working with large framing members. The framing square setting figures are based on the pitch over the length of the hip per foot of run. It's helpful to master this, especially if the framing calls for a valley beam to be V-cut, required when exposed below.

Walk, Then Run

So why bother using a framing square when several modern tools–those designed for specific tasks–leave the square in the dust? I own most of the modern tools and wouldn't build without them. However, using these tools doesn't require you to understand the principles that guide them; in fact, they shortcut the knowledge that builds true understanding of the craft. Master the framing square and you'll make your construction calculator 10 times more powerful.

–Don Dunkley is a veteran framer and is the construction events manager for Hanley Wood's JLCLive! and The Remodeling Show. He lives in Dallas.