Transcript Unit 48 — Hip Roofs

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Unit 48
Hip Roofs
Hip Rafters • Hip Jack Rafters •
Constructing Hip Roofs
Unit 48 — Hip Roofs
A hip roof has four sloping sides. Four hip rafters run
at a 45° angle from the exterior walls. Hip jack rafters
frame the space between the hip rafters and the top
of the exterior walls.
Unit 48 — Hip Roofs
Side cuts are
required at the
ridge and tail of
a hip rafter.
Unit 48 — Hip Roofs
The unit run of a hip
rafter is 17″, which is
the 45° diagonal of a
12″ square.
Unit 48 — Hip Roofs
To calculate the actual hip
rafter length, one-half the
diagonal thickness of the
ridge board that fits
between the rafters is
deducted from the
theoretical length. When
shortening the hip rafters,
make the measurement
perpendicular to the
plumb line, not along the
length of the roof member.
Unit 48 — Hip Roofs
When laying out a hip
rafter, the angles for side
cuts and ridge plumb cuts
are marked first.
Unit 48 — Hip Roofs
The rafter table on a framing
square can be used to determine
the exact angle for the side cut of
a hip rafter. The roof in this
example has a 7″ unit rise.
Unit 48 — Hip Roofs
A hip rafter overhang
runs 1.42″ for every
1″ of common rafter
run. In this example,
the run of the
common rafter is
10″. To find the run
of the hip overhang,
multiply 1.42″ by 10.
The result is 14.2″,
or 14 1/8″.
Unit 48 — Hip Roofs
A framing square
can be used to
calculate the run
of the hip rafter
overhang. In this
example, the run
of the roof
overhang is 10″.
Unit 48 — Hip Roofs
Backing a hip rafter
allows roof sheathing to
lie in the same plane as
common and jack rafters.
Unit 48 — Hip Roofs
Dropping a hip
rafter is faster than
backing a rafter
and accomplishes
the same purpose.
Unit 48 — Hip Roofs
When calculating lengths of
hip jack rafters for layout
beginning from the common
rafter at the end of the
ridge, the common length
difference must first be
determined. In this
example, the roof has a 6″
unit rise and a 20′-8″ span.
The length of common
rafters is 11′-6 5/8″. The hip
jack rafters are spaced 24″
OC. The common length
difference is 26 13/16″.
Unit 48 — Hip Roofs
Hip jack rafter layout can begin from a common rafter
located away from the end of the ridge board. In this
example, the roof has a 5 unit rise and 23′-0″ span.
The hip jack rafters are spaced 24″ OC. The common
length difference is 2′-2″.
Unit 48 — Hip Roofs
When calculating hip jack rafter
length beginning from the corner
of a building, the length of each
succeeding hip jack rafter length
is increased by the common
length difference. In this
example, the roof has a 6″ unit
rise. The hip jack rafters are
spaced 24″ OC. The 26 13/16″
or 2′-2 13/16″ common length
difference shown in the rafter
table is the length of the first hip
jack rafter placed 24″ OC from
the corner of the building.
Unit 48 — Hip Roofs
Hip jack rafters
require a single
side cut where
they fasten to the
hip rafter. In this
example, the roof
has a 4″ unit rise.
Unit 48 — Hip Roofs
A hip jack rafter has plumb
cuts where it fastens to the
hip rafter as well as cuts at
the heel and tail.
Unit 48 — Hip Roofs
When calculating the theoretical ridge board length of
a hip roof, subtract the total span from the total length
of the building. In this example, the total span of the
roof is 22′ and the total length of the building is 45′.
Unit 48 — Hip Roofs
Different calculations are used when a common rafter
is installed at the end of a ridge board than when a
common rafter is not installed at the end.
Unit 48 — Hip Roofs
When constructing a hip
roof, the main framing
members should be precut
before construction begins.