Glencoe: Sections 67 A: Flashcards
Before cutting rafters, a carpenter must determine what kinds of rafters are needed X
to frame the roof.
Laying out a roof framing plan:
Gable Roof:
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The gable roof framing plan is the simplest to develop.
- X
- Determine the direction in which the X
- Draw the centerline at right angles to this direction (B). The centerline determines the X
This corresponds to the location of the ridge board. - Determine the X and lay out the roof frame plan D.
Lay out the outline of the building (A)
rafters will run
location of the ridge line (C).
distance between the rafters
Laying out a roof framing plan:
Gable and Valley Roof:
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A gable and valley roof is simply
two gable roofs that intersect
Laying out a roof framing plan:
Gable and Valley Roof:
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1. X
- Draw the centerline of the X (B, arrow 1)
- Draw the centerline of the X (B, arrow 2.)
- Draw 45deg lines from the X to where the centerlines intersect (C).
- Draw the X (D).
- Determine the distance between the X and lay them out on the roof framing plan (E).
Lay out the outline of the building (A).
larger rectangle
smaller rectangle
interior corners of the building
ridge lines
rafters
Laying out a roof framing plan:
Hip Roof:
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The angle at which the hip extends from each corner is usually Xdeg. However, other angles are possible. A Xdeg angle will insure that each X
If the angle is something different than 45deg, the slope will
45deg
surface of the roof will have the same slope.
not be the same.
Laying out a roof framing plan:
Hip Roof:
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1. X
- Locate and draw a X
- Start at each corner, draw a 45deg line from the corner to the centerline (C). This establishes the location of the X
- Draw the X between the intersecting points of the hip rafters (D).
- Determine the distance between X and lay them out on the roof framing plan (E).
Lay out the outline of the building (A)
centerline (B)
hip rafters.
ridge line
the rafters
Laying out a roof framing plan:
Hip Roof:
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A hip and valley roof can be quite complex. It is created when one or more hip roofs X, as shown in on page 473.
intersect at 90deg
Laying out a roof framing plan:
Hip Roof:
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1. X
- Outline the X inside the building outline (B).
- Draw centerlines for every X formed inside the building outline (C).
- Draw a 45deg line from each X. Extend these lines to intersect with the centerlines (D). The lines indicate the location of the X on outside corner and x on inside corners.
- The centerlines drawn in (C) connect the X, Draw these as solid lines where the ridges will be located (E)
- Figure the distance between the X and lay them out on the roof framing plan(F)
Lay out the outline of the building (A).
largest rectangle
rectangle
inside and outside corner
hip rafters
valley rafters
hip valley rafters
rafters
Laying out a roof framing plan:
Hip Roof:
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During the layout and assembly of a roof frame, a great volume of lumber is handled. Due to their size and length, rafters are X
Organize the work to minimize the back strain. For example, have lumber delivered close to where it will be cut. Work with a helper to lift rafter into position.
much heavier than wall studs and far more unwieldy.
In conventional roof construction, carpenters assemble the roof from individual ceiling joists and rafters.
The rafters should not be erected until X. The ceiling joists act as a tie to prevent the rafters from X.
the ceiling joists have been fastened in place
pushing the exterior walls outward
The rafters form the X. They must be carefully made and fitted if they are to support the roof’s weight. The top of the rafter rests against the X, as shown in Visualizing Rafter Cuts.
skeleton of the roof
ridge board
Plumb cut:
The cut made in the rafter so its fits against the ridge is called a
The bottom of the rafter rests on the
plate.
Level cut or seat cut:
The cut at the bottom of the rafter that rests on the top plate
Laying Out Common Rafters:
Plumb cut:
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A line for the plumb cut can be drawn using a framing square as a guide.
The unit run (12” mark) on the blade of the square is aligned with the X.
The unit rise on the tongue of the square will correspond to the X of the roof. The unit rise is aligned on the same edge of the rafter. The line for the plumb cut is then drawn along the edge of the tongue.
edge of the rafter
pitch
Laying Out Common Rafters:
Seat cut
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A line for the seat cut is drawn with the square in the X on the rafter but with the square in a X. The line is drawn along the body of the framing square as shown in B making Plumb and Seat Cuts.
same orientation
different location
Theoretical rafter length:
The shortest distance between the outer edge of the plate and a point where the measuring line of the rafter meets the ridge line.
The theoretical rafter length may be calculated in the following ways:
By using X
By using the X obtained from the rafter table on the framing square
By X with the framing square
By entering the X.
Pythagorean theorem
unit length
stepping off the length
rise and run into a calculator designed for solving construction problems
Laying Out Common Rafters:
Builders: Tip
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Another type of framing square.
Some carpenters find a triangular framing square easier to use and more convenient to carry. Another advantage is that the thickened lip along one side allows it to be used to X when crosscutting lumber.
One brand of triangular framing square is called a X. To make a plumb cut with a triangular framing square, hold the square’s X against one edge of the rafter stock.
Pivot the square until X. As shown here, the rise is 6-in-12 mark the rafter from the pivot point along the top edge of the square. This is the plumb line.
guide a circular saw
speed square
pivot point
the appropriate rise number on the “common” scale of the square lines up with the same rafter edge
Laying Out Common Rafters:
Pythagorean Theorem method:
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How to calculate the rafter from Pythagorean theorem.
A = unit rise
B = unit run
C(rafter unit length) = sqrt(A^2 + B^2)
Laying Out Common Rafters:
Unit-length method:
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The unit-length method uses the X.
rafter table on a framing square
Laying Out Common Rafters:
Unit-length method:
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Unit length:
Unit length is the length of a rafter per foot of run. It can be expressed as the hypotenuse of a right triangle.
Laying Out Common Rafters:
Unit-length method:
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The unit run is the X of the rafter,
and the unit rise is the X of the rafter.
base
altitude
Laying Out Common Rafters:
Unit-length method:
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How to read a framing square.
The inch marking along the top that reads “common rafters per foot run” represent:
If you X to the figure under 6 (for a unit rise of 6”) you will find the number 13.42
The inch marking along the top respresent the unit rise.
follow across the top line
Laying Out Common Rafters:
Unit-length method:
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Unit run is always Xin
12” inch
Laying Out Common Rafters:
Unit-length method:
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How do you get the total length:
Remember that X must be added to the calculated rafter length, and X must be subtracted to determine the true total length.
The unit length times the total run.
overhang
half the ridge width
Laying Out Common Rafters:
Step-off method:
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A third method for finding the theoretical rafter length is by using the framing square to “step off” the length, as shown on page 478.
Place the square on the rafter with the tongue along the X. Step off the length of the unit run on the rafter stock as many times as there are feet in the total run.
plumb cut
