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NO OF JOIST STUD & RAFTER N FT-IN table on the framing square blade back - explained here (C) Daniel Friedman at InspectApedia.comFraming Square NO OF JOIST STUD & RSFTER FT-IN Table Guid
Table giving The Number of Joists, Studs, Rafters Required

What is the table found on the framing square blade back that reads "NO OF JOIST STUD & RAFTER N RUN FT-IN " and how do we use it.

A carpenter's framing square includes tables stamped right into the tool itself. This article series 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.

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How to Use the NO OF JOIST STUD & RAFTER N RUN FT-IN Table

Number of joists, studs, or rafters N run (C) Daniel Friedman

The Number of Joists, Studs, Rafters N Run Ft-In Table on a Framing Square Blade Back

Found beginning under the 2-inch column on the back of a framing square blade and extending to below the 8-inch column of data is a table titled

NO OF
JOIST
STUD &
RAFTER
N RUN
FT-IN

I had a devil of a time finding details on this table - I have asked Empire who made this square, for help. Readers who have information are asked to contact us. Home Depot data for this Empire Framing Square shows this table described as "Conversion Tables for Common Application Needs" but gives no more detail.

It is disappointing that Empire, the framing square manufacturer never responded to any of our several requests on this.

Below we explain that we think this table gives The number of framing members N in a floor, ceiling, wall or roof of width (or "run") W.

Found under the 3-inch column on the black of the framing square blade we see

Under the 3" Column we find

5 5-4
6 6-8
7 8-0
8 9-4
9 10-8
10 12-0

Reading under the 4", 5", 6", 7", and 8" columns on the framing square blade back you'll see that data table continuing up to

40 52 0

These numbers appear to give the number of floor or ceiling joists, wall studs, or roof rafters in a distance (across the framing member) of Ft - In.

So the table is read as

Examples:

5 5-4 = 5 studs are required to frame a wall that is 5' 4" wide.

7 8-0 = 7 studs are required to frame a wall that is 8' 0" wide.

17 21-4 = 17 studs required to frame a wall that is 21' 4" wide.

 

Here are example calculations supporting this view, suggested by readers cited below

Matt said:

It may seem too obvious but it looks to me like it;s simply a calculation to determine the run based on number of studs, joists or rafters on 16" centre.

eg.

17 joists (16 joist cavities) would simply be 16x16" = 256"/12" = 21'4"

6 joists (5 joist cavities) would be 5x16" = 48"/12" = 6' 8"

Denis Hagy said:

The numbers in the "N-Joists" table are based on 16" centers....i.e., 7 8-0 for an 8 ft. 0" wall, end to end, 1 to start + 96" (8 ft) /16" = 6, thus 7 studs required;

Moderator offers calculation details:

Question: how many studs will I need to build wall that is 8 '0" long?

Answer from the table: 7 studs

Supporting Calculation:

Using 16" o.c. framing

N = Nr. Studs (or "framing members") in an 8' 0" wall using 16" o.c. framing.

W = Wall width in inches = ( 8 x 12) = 96"

D = Stud or joist or rafter on-center framing interval, normally 16" o.c.

We add 1 to W/D to get the number of framing members because we need one more member at the start (or end) of the framed unit = 1 more member than number of stud, joist, or rafter bays.

N = 1 + W / D

N = 1 + 96" / 16"

N = 1 + 6

N = 7 studs.

Try it for the other numbers:

40 52 0; 39 16" increments in 52 ft. + 1 starter = the 40 studs [or rafters]

At the end of this article atReferences or Citations you'll find more texts and articles on using a framing square and written by other experts.


...

Continue reading at FRAMING SQUARE USER'S GUIDE - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Building & Roof Measurement Articles

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FRAMING SQUARE N JOISTS RAFTERS N RUN FT-IN at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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