1. Rafter Marking Information Technology and Communication Services
By Dave Wilson
Information Technology and Communication Services
ITCS Instructional Materials
College of Agricultural, Consumer and Environmental Sciences
University of Illinois at Urbana-Champaign
Copyright ® University of Illinois Board of Trustees
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2. Table of Contents III. Gable rafter marking steps IV. Collar tie
A. Marking a collar tie
V. Shed Roof Rafters
VI. Shed rafter marking steps
VII. Parts of a Building
I. Purpose
II. Gable Roof Rafters
A. Ridge piece
B. Plate
C. Roof slope
D. Marking line
E. Length of rafter
F. Birdsmouth
G. Overhang
H. Fascia and Soffit
I. Types of tails
J. Roof pitch table 03 04 05 06 07 10 12 14 15 17 21 22 23 39 40 43 47 61
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ITCS Instructional Materials College of Agricultural, Consumer and Environmental Sciences University of Illinois at Urbana-Champaign

3. The purpose of this presentation is to identify rafter parts,
building parts, and one method of marking gable and shed
style rafters. The presentation will focus on:
identifying gable rafter parts
parts of the building required to mark a rafter
roof pitch
marking a gable rafter
identifying shed rafter parts
marking a shed rafter
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4. Gable Roof Rafters Rafter Rafter
Gable rafters are normally equal in length, each spanning an
equal distance of the building. Exceptions to the rule exist and
require only small adjustments to be marked.
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5. Ridge Piece Ridge piece
Ridge piece lumber is normally two inch lumber and wide enough
to receive the full depth of the rafter.
dressed - 1 1/2 inches thick
nominal - full cut or 2 inches thick
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6. Plate
Most buildings are constructed with double plates to tie the corners
of the building together. The plate directly supports the rafters and
will commonly be nailed to the top of the wall studs.
Upper plate
Wall stud
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7. Roof Slope Rise Slope triangle C L Span Run Roof pitch is normally
given as a triangle, stating
the number of inches of rise
per foot of run.
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8. Run, Span & Rise of a Gable Roof
Run is the horizontal distance under the rafter extending from
the outer edge of the building to a plumb line from the center
of the ridge piece. Total run of a rafter is 1/2 the span of the
building.
Span is the distance from one outside wall to the outside wall
on the other side of the building. The span is the width of the
and is two times the length of the run.
Rise is the vertical distance from the top of the plate to the
marking line at the ridge piece.
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9. Rise, Run & Span 09 Rise Run Span Centerline
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10. Marking Line
Marking line
The marking line is located 1.5 inches from the bottom of a 2-inch
x 4-inch rafter and 2 inches from the bottom of 2-inch x 6-inch
or larger rafter.
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11. The marking line is drawn onto the rafter pattern prior to
marking rafter parts. A common tool used to draw the marking
line is the framing square and a lead pencil. The tongue of a
framing square is 1.5 inches wide and the blade is 2 inches wide.
The marking line is always drawn on the lower side of the rafter,
preserving the largest amount of rafter to support the building roof.
The marking line can be used as reference line to mark the upper
and lower plumb cuts and the depth of the bird’s mouth.
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12. Length of Rafter 12 Rafter length Rafter tail
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13. Length of Rafter
The length of the common rafter is the shortest distance between the outer edge
of the plate and the centerline of the ridge piece.
The length of each rafter must be adjusted to allow room for the ridge piece.
Adjusting rafter length subtracts one-half the thickness of the ridge from
each rafter. (Caution is recommended to avoid errors when correcting the
length of the gable rafter.)
The actual length of the rafter is a bit shorter than the theoretical length of the
rafter.
The rest of the rafter is called the rafter tail.
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14. Birdsmouth Plate level Birdsmouth 14
Birdsmouth is the name given to the notch cut
into the rafter where it is to sit on the plate.
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15. Overhang Outside wall Overhang Fascia line
Overhang is measured on a horizontal line.
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16. Overhang The overhang is sometimes called the projection.
Overhang is the horizontal distance from the outside wall to the fascia line.
When the rafters overhang the building, the overhang helps to form the eaves
or cornice and this sheds the water away from the building.
The overhang also provides shade to keep the sun from shining on the upper
part of the side wall of the building.
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17. Cuts for Trim Fascia Fascia Cut Soffit cut Soffit Plancher level 17
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18. Cuts for Trim
The vertical cut on the end of the rafter is the fascia cut. The fascia cut is
normally plumb. The fascia or trim board is nailed to the rafter along this
vertical cut.
If the cornice is to be enclosed, the horizontal cut on the rafter is called a
soffit cut.
The imaginary horizontal line is called the plancher level and sometimes the
board that is used to enclose the cornice is called the plancher or soffit.
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19. Gable Rafter Cuts Ridge cut (upper plumb cut) Heel Plumb cut Seat cut
Tail cut
(lower plumb cut)
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20. Gable Rafter Cuts
The ridge cut is sometimes called the upper plumb cut. This cut must be
perpendicular to the earth, hence the name plumb cut.
The cut at the lower end of the rafter is called the tail cut. There are different
styles of tail cuts.
The heel of the rafter sits on the plate and the cut that is parallel to the top of
the plate is called the seat cut.
The other part of the birdsmouth is a plumb cut and it is marked by applying
the square in a similar manner to the way the ridge and tail cuts are made.
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21. Types of Tail Cuts Parallel to Plumb cut Parallel to Seat cut
Combination cut
Square cut
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22. Roof Pitches This table gives the pitch for various rises
Blade
This table gives the pitch for various rises
of roof from 1 inch to 24 inches per foot
of run. It can be seen from this table that
a rafter rise of 12 inches per foot of run is
equivalent to 1/2 pitch (12 over 24). This
is the same as a 45-degree angle.
12 = 1/2 45º 0´ 1/2
Tongue
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23. Marking a Gable Roof Rafter
Step #1
The example problem will be marked with a 6-inch rise
per foot of run.
Mark here
Dot goes here
The dot marks the length of the
overhang, 16 inches.
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24. Marking a Gable Roof Rafter
Step #1
In this example we have a slope triangle with a 6-12 slope.
Step one includes placing the marking line onto the rafter lumber.
When marking a rafter using a framing square be alert to use both numbers
on the outside of the square or from the inside set of numbers on the square.
Starting at the bottom, rafter tail, end of the rafter place the framing square
onto the marking line so that the 6 inch mark and the 12 inch mark intersect
with the marking line. The 6 inch mark needs to face the outside of the
building (lower end of the rafter).
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25. Marking a Gable Roof Rafter
Step #1 Continued
Mark the lower plumb cut using a pencil and checking to be sure the square
numbers both on the outside or inside of the square and properly aligned on
the marking line.
While holding the square in this position the back of the birdsmouth or
overhang length can be marked. Remember this distance is always horizontal and
perpendicular to the plumb line of the outer wall.
In the example problem the overhang is 16 inches and marked with a dot
on the rafter. It is important to mark the overhang length using the same side
of the square as the pitch, 6-12 are being aligned.
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26. Marking a Gable Roof Rafter
Step #2
Marking the back of the birdsmouth.
Mark here 12 6
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27. Marking a Gable Roof Rafter
Step #2 Continued
Step 2 marks the back of the birdsmouth and can be done without lifting
the square from the rafter.
The square is slid toward the center of the rafter keeping the pitch, 6-12,
lined up on the marking line until the blade of the square intersects the
dot from step #1, marking the back of the birdsmouth.
Draw a line from the marking line to the bottom of the rafter to create the
back of the birdsmouth, this will be a plumb cut and parallel with the lower
plumb cut. This can be checked visually.
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28. Marking a Gable Roof Rafter
Step #3
Marking the seat cut. 6 12
Mark here
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29. Marking a Gable Roof Rafter
Step #3 Continued
Marking the seat cut creates a horizontal line parallel with the top of the plate.
Rotate the square so the tongue is facing the center of the rafter.
Align the 6 on the tongue and the 12 on the blade of the square with the marking
line.
Slide the square on the rafter until the outside of the tongue aligns with the
intersection of the marking line and the plumb line at the back of the birdsmouth.
Draw a line from the back of the birdsmouth to the lower edge of the rafter.
This marks the heel of the rafter and is called the seat cut. The triangle created
should look similar to a door wedge.
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30. Marking a Gable Roof Rafter
Step #4
Dot
Calculating rafter length 12
Rafter length
3/4” 6
The dot marks rafter length.
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31. Marking a Gable Roof Rafter
Step #4 Continued
Gable rafter length is determined using the slope triangle, rafter table (from the
framing square), the run of a building, and the thickness of the ridge piece.
Rafter length = (Square reading x run) minus 1/2 the thickness of the ridge piece.
Look at the framing square and locate the rafter table, front side of the blade.
The top line should be labeled “LENGTH COMMON RAFTERS PER FOOT
RUN.”
Follow the common rafter line to the right to the column of numbers under the
6-inch mark on the outside edge of the blade. The first number should be
13 42, this represents inches of rafter length per foot of run.
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32. Marking a Gable Roof Rafter
Step #4 Continued
The column under the 6 was selected because 6 inches of rise per foot of run
equals the pitch of the roof in the example problem.
The means for each foot of run, the rafter is inches long.
Calculate the rafter length (for building run) by multiplying times
the number of feet of run in the building.
Measure the rafter length with a steel tape from the corner of the birdsmouth
along the marking line. Mark the length with a dot.
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33. Marking a Gable Roof Rafter
Step #4 Continued
The length of the rafter must now be adjusted for the thickness of the ridge
piece.
The ridge piece is parallel with the upper plumb cut, therefore the adjustment
to the rafter must be parallel to the upper plumb cut. Use the framing square
to mark this adjustment.
Place the square on the rafter aligning the 6 and the 12 with the marking line.
(The tongue, 6-inch mark, should be toward the center of the rafter.)
Slide the square along the rafter until the blade intersects the dot marking the
length of the rafter.
The blade of the square should be parallel with the heel of the birdsmouth.
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34. Marking a Gable Roof Rafter
Step #4 Continued
With the blade of the square lined-up with the mark indicating rafter length,
follow along the blade of the square 3/4 inch toward the center of the rafter,
for dressed ridge lumber, marking the rafter with another dot.
The rafter was shortened by 1/2 the thickness of the ridge piece.
The new dot will represent the adjusted length of the rafter. Mark the
spot on the rafter to draw the upper plumb cut.
The mark representing the adjusted length of the rafter will not be located on
the marking line. The new dot should be located above the marking line
toward the top of the rafter.
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35. Marking a Gable Roof Rafter
Step #5
Marking the upper plumb cut
Mark 6
3/4 inch 12
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36. Marking a Gable Roof Rafter
Step #5 Continued
The square should be placed on the rafter with the blade toward the center
of the rafter.
Align the 6 and the 12 with the marking line, double checking to use numbers
on the same side of the square.
Slide the square on the rafter until the tongue intersects the mark indicating
the adjusted length of the rafter and draw a plumb line across the rafter
using a pencil.
Visually check to assure the upper plumb line is parallel to the lower plumb
line and the plumb line is marked at the birdsmouth.
The seat cut at the birdsmouth should be perpendicular to the plumb line.
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37. Marking a Gable Roof Rafter
Step #6
Marking trim cuts
Mark
Dot 6 12
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38. Marking a Gable Roof Rafter
Step #6
When a soffit is to be used and you wish to cut the rafters so that the soffit can
be nailed to the underside of the rafters OR if you wish to cut the rafter so that it
does not extend below the fascia board as shown in slide #37, then mark the
soffit cut line following the directions listed below.
Apply the square with the 6 and 12 marks on the inside of the square along
the lower plumb cut at the marking line.
Make a horizontal mark from the marking line to the lower edge of the rafter
this will be horizontal to the seat cut at the birdsmouth.
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39. Collar Tie
The function of the collar tie is to hold the two rafters together.
Collar tie
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40. Marking a Collar Tie Mark Dot 40 24 12 12 6
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41. Marking a Collar Tie
If the builder wants to locate the collar tie 12 inches below the ridge piece,
he/she would apply the square to the ridge piece or to the upper plumb cut on the
rafter. This way the 12 inch mark on the outside of the tongue of the square is
even with the lower edge of the rafter and the 24 inch mark on the outside of the
blade just touches the lower edge of the rafter.
Place a dot on the edge of the rafter at the 24 inch mark.
The carpenter then rotates the square and lines the 6 inch and 12 inch marks
on the outside of the square even with the upper edge of the rafter.
Slide the square up until the blade of the square is even with the dot on the
lower edge of the rafter.
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42. Marking a Collar Tie Continued
Place a mark across the rafter at this point.
This mark will be the horizontal to the heel of the rafter and will be 12 inches
below the ridge piece.
This is the location for the collar tie.
This mark should be made on both rafters and the collar tie can be nailed on
these two lines.
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43. Shed Roof Rafter Rafter length Front plate Overhang Marking line
Rear plate
Overhang
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44. Shed Roof Rafter
A shed roof rafter rests on two fixed points, the rear plate and the front plate.
Since the front and rear plates are fixed points, the length of the rafter is
measured from the upper edge of the rear plate to the upper edge of the front
plate.
The front and rear overhang of the rafters must be added to the length of the
rafter as shown in the illustration.
The rear overhang is measured from the outside of the rear plate while the front
overhang is measured from the inside of the front plate.
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45. Run, Span and Rise Shed Roof Rise Run Span 45
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46. Run, Span and Rise Shed Roof
The rise of a shed roof is the difference in height of the rear and front plates.
The run is measured horizontally from the rear edge of the rear plate to the
rear edge of the front plate.
Although a shed roof slopes on only one direction the run and the span of the
rafters are not the same quantities.
The span represents the entire width of the building, while the run of the rafter
is shown in the illustration.
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47. Marking a Shed Roof Rafter
Step #1
The problem for the illustration will have a 2–10 slope and an 8 inch
overhang on each end.
Dot
The dot marks the amount of overhang and the location
for the plumb cut in the birdsmouth.
Mark
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48. Marking a Shed Roof Rafter
Step #1
Draw a marking line on the rafter. This can be done by drawing along the blade
of the square which is held even with the top side of the rafter on 2-inch by 4-inch
rafter lumber. Place the square along the bottom side of the lumber if it is a 2 inch
by 6 inch or wider member.
Notice the pitch is a 2 – 10 slope. Multiples of the pitch ratio can be used with no
loss in accuracy. 4 and 20 will be used in the example problem.
Place the 4 inch mark and the 20 inch mark on the marking line and mark the
lower plumb cut near the end of the rafter.
Measure 8 inches over horizontally on the outside of the square and place a dot on
the rafter even with the 8 inch mark. This locates the birdsmouth on the rafter.
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49. Marking a Shed Roof Rafter
Step #2
Marking the birdsmouth
Mark
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50. Marking a Shed Roof Rafter
Step #2
Slide the square up the rafter with the 4 inch and 20 inch marks on the marking
line until the dot is just visible on the outside of the square.
Place a line from the marking line to the lower edge of the rafter using a pencil.
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51. Marking a Shed Roof Rafter
Step #3
Mark
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52. Marking a Shed Roof Rafter
Step #3 Continued
Rotate the square, to place the blade facing toward the bottom of the rafter,
and place the 20 inch mark and the 4 inch mark on the marking line.
Slide the square until the upper edge of the square intersects the mark locating
the plumb cut at the back of the birdsmouth.
Draw a horizontal line from the back of the birdsmouth to the lower edge of
the rafter. This marks the seat cut.
Visually check to verify that the birdsmouth is wedge shaped with the seat
cut line perpendicular to the plumb cut. All plumb cuts should be parallel.
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53. Marking a Shed Roof Rafter
Step #4
Rafter length
Mark here
Rafter
length
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54. Marking a Shed Roof Rafter
Step #4 Continued
Shed rafter length is determined by multiplying the square reading, length per
foot of run, times the building run in feet.
Square Reading x Run = Rafter Length (inches)
Measure the distance from the rear corner of the lower plate to the rear corner
of the upper plate with a tape measure. This distance is the length of the rafter
from one birdsmouth to the other.
Mark this distance on the marking line at the upper end of the rafter using a
pencil dot on the marking line.
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55. Marking a Shed Roof Rafter
Step #4 Continued
Mark the upper birdsmouth at the dot marked on the rafter.
Arrange the square on the rafter with the blade end facing the top end of the
rafter and the 4 inch and 20 inch marks aligned on the marking line.
The tongue should be parallel with all plumb cuts.
Slide the square on the rafter so the dot, top end of rafter length, is just
visible and draw horizontally from the marking line to the bottom edge
of the rafter.
This line represents the seat cut for the top end of the rafter.
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56. Marking a Shed Roof Rafter
Step #5
Marking the top birdsmouth
Mark
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57. Marking a Shed Roof Rafter
Step #5 Continued
Rotate the square, blade facing the center of the rafter, and place the 4 inch
and 20 inch marks on the marking line.
Slide the square on the rafter until the tongue, parallel to all plumb lines,
intersects the point on the marking line that indicates the inside corner of the
upper plate.
Draw a line on the rafter at this point marking the plumb cut for the upper
birdsmouth on the rafter.
Visually check to be certain that all plumb lines are parallel and the horizontal
lines are parallel.
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58. Marking a Shed Roof Rafter
Step #6
Marking the upper overhang
Mark
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59. Marking a Shed Roof Rafter
Step #6 Continued
Use the 2 inch and 10 inch marks representing the rise and run of the rafter
and slide the square until these inch marks are along the upper edge of the
rafter.
The overhang for this building is 8 inches from the outside of the plate/stud.
This distance plus the width of the plate/stud, 3.5 inches, will determine
where to mark the top end of the rafter. (8” + 3.5” = 11.5”)
The overhang for this building should be 11.5 inches from the rear of the
upper plate.
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60. Marking a Shed Roof Rafter
Step #6 Continued
Slide the square along the marking line keeping the 4 and the 20 aligned
on the marking line, until the distance from the plumb cut of the upper
birdsmouth is just visible at the 11.5 inch mark on the square.
Draw a plumb line across the rafter marking the upper plumb cut.
The upper plumb cut should be plumb and parallel with the lower plumb cut.
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61. Parts of a Building Rafter Plate Sill
The footing, foundation, sill, and
stud wall are the supporting structure
for the roof (rafters).
Foundation
Footing
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62. Prepared by Dave Wilson
This set of images was drawn by the Department of Agricultural Engineering,
University of Illinois. It may be used to supplement “Using the Carpenter’s Square,”
U3009a, available from ITCS Instructional Materials.
Prepared by Dave Wilson
QUIT
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GJA