How to use a framing square.

A framing square is a lot more than a simple square-cut saw guide. This simple device is crammed with tables, data and tricks that allow a carpenter to lay out roof rafters, stairs, or other building features.

A carpenter's framing square includes tables stamped right into the tool itself. This article explains how to make quick use of a framing square and its imprinted data to get some basic roof measurement data like roof pitch or slope, rafter lengths, and end cuts, stair stringer cuts, lengths of braces and other construction measurements.

What is the Essex Board Measure on the Back of a Framing Square Blade: Board Feet

Here we describe the Essex Board Measure tables found on some framing squares - data allowing you to determine the number of board feet in lumber.

On both the long and short arms of the framing square are marked various framing tables giving rafter lengths, roof slopes and the proper angle of cuts for various roofing connections such as a rafter end abutting the ridge board, the birds' mouth cut at the rafter segment that rests atop a wall plate, hip and valley rafter cuts and other information.

Found on the back of some older framing square blades - but not on most modern framing squares, the Essex Board Measure will tell you the number of board feet for lumber of various lengths, widths, thicknesses.

Definition of board feet

One Board Foot is the volume of wood that is found in a one-inch thick square that is 12x12 inches in length and width. In other words one square foot of wood that is one inch thick is one board foot.

How to Read & Use the Essex Board Foot Table

1. Find the length of your board, e.g. 14 feet long, under the 12-inch mark on the blade back top edge.
2. Look left or right in the same table row, still reading along the top of the blade, to find the width of your board, look. e.g. under the 8" mark is data for boards that are 8-inches wide
3. Read down under the 8" mark from the blade top to same (14 foot length) row that you chose earlier and note the pair of numbers there giving Board Feet and Fractions-of-a-board foot-in-twelfths, such as 9 4 that would indicate 9 and 4/12 board feet

If your board is just 1" thick you've got the answer, 9 4/12 board feet in a 1" x 8" x 14' board.

If your board is 3" thick you need to measure and add the feet and inch figures from the table by three.

For a 3" thick board, 3' x 9bf = 27 (board feet) to which we must add 3" x 4 (twelfths of a board foot) = 12 board inches

So our 3" thick board is 27bf and 12/12ths board feet or, by careful planning in this example we can round up to 28 board feet or bf.

Below for clarity, using the same board example as above, we illustrate how & where to read board width, board length, and board feet on the Essex Board Measure table on framing squares.

Today few people care about board feet but that used to be a way that lumber was sold. The Essex Board Measure tables would allow you to convert a conventional framing member, such as a 2x4 into board feet.

Watch out:

• Before 1924 a 2x4 was usually a true 2" thick by 4" wide. Or slightly less than 4".
• Then up to 1970 the size of a 2x4 was 1-5/8 x 3-5/8
• In 1970 the minimum dressed size was related to moisture content and this lead to a dry (19% MC or less) 2x4 being 1-1/2 x 3-1/2

Details are at FRAMING AGE, SIZE, SPACING, TYPES where we explain how and why the actual physical dimensions of framing lumber have changed over time.

History of the Essex Board Measure Tables

Watch out: Some texts re-phrase the Essex Board Measure table as giving the correct number of square feet in boards - a phrasing I find confusing. To keep things straight in your own more-clear mind, just remember that

One Board Foot = a 12" x 12" x 1" thick piece of wood.

The purpose of board feet was to provide a standard volumetric measurement or quantity of wood when the wood could be in various forms.

For example an expert logger could look at a tree or measure its diameter and height and come up with an accurate estimate of the number of "board feet" that tree would yield.

It made not one whit of difference to the logger whether the tree was going to be sawn into one giantic beam or into 2x4s or into lath strips.

• Sigmon, Dallas L. COMBINATION SQUARE [PDF] U.S. Patent 2,251,208, issued July 29, 1941. Ilustrates that Sigmon continue sophisticating framing square designs for many decades.
• Sigmon, Dallas L., A Framing Guide and Steel Square, a practical treatise giving shortest methods on roof framing and how to use the steel square. Rafter tables, square root tables, sash tables, shingle tables, and various tables,... Birmingham (1908) on carpenters' squares and roofs.
• U.S. Army, CARPENTRY [PDF] (1995) retrieved 2019/09/10 original source: https://www.marines.mil/portals/1/MCRP%203-17.7C%20z.pdf
• U.S. Navy, ROOF FRAMING [PDF] NAVEDTRA, Naval Education & Training, includes detailed examples of using the framing square and framing square tables
• U.S. Navy, ROUGH CARPENTRY [PDF] NAVEDTRA, Framing Sills, Framing Floors, Framing Walls, Framing Roofs, Using the Framign Square, Laying out and Installing Roofs, Roof Trusses, Framing Stairs, retrieved 2019/09/10, original source: http://navybmr.com/study%20material/14043a/14043A_ch10.pdf

 

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Continue reading at HOPPUS MEASURER for another early board measurement guide, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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Suggested citation for this web page

FRAMING SQUARE ESSEX BOARD MEASURE at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ROOFING

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