Roof Framing
Roof Types
Gable Roof
Assembly
The Anatomy of
a Common
Rafter
Common Rafter Layout
To lay out a common rafter, you need the pitch of the
roof, expressed in units of rise per foot of run. a rafter
with 6-in-12 pitch rises 6 in. for every foot of run. Run
is the horizontal distance that the rafter covers. For a
gable roof, the run is measured from the centerline of
the ridge board to the outside edge of the top of the
wall.
Framing Square Pitch
Rafter Length
“Stepping Off”
Stepping off the rafter
Start at the ridge. Clamp stair gauges to the framing
square to align rise and run measurements with the
rafter’s top edge. Mark the first plumb line near the
end of the rafter to locate the ridge cut. Then mark
the first 1-ft. increment of run. Now you can “step
down” the rafter to complete the total run.
Rafter Length
Using…
RISE
Pythagorean Theorem
A2 + B2 = C2
RUN
Example: If A=3 , B=4 then what would c=?
16 + 9 = 25 then C= sq root of 25 which is 5
Plumb cut
 Trim the plumb cut to
account for the ridge
board. Half of the ridge
board’s thickness must
be removed from the
plum cut of the rafter.
Seat Cut
 Plumb and seat cuts complete the bird’s mouth. The
right-angled notch that fits over the top of the wall is
called a bird’s mouth. Measuring from the plumb cut,
make the level seat cut equal to the thickness of the
wall assembly.
Speed Square “Birds Mouth”
Eave / Overhang
 Mark the overhang.*Some framers prefer to leave the
tails long, then snap a line and cut them in place.
Cut, Rinse and Repeat
Cut the first one with extra care. This rafter will serve as
a pattern for all the others, so it’s important to make
precise cuts.
The Common Rafter
Eave Blocking
Shed Roof
Shed Roof
Cripple Wall
16”
8’
Cripple Wall
Hip Roof
Hip Roof
Trusses
Installing Trusses
Lookouts / Outriggers
Collar Ties
Gable End Bracing
Rafter Support
Ceiling Joist
Ceiling Joist
Supports
Ceiling joist DON’T