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17 Basic Roof Framing
Section 17.1
Planning a Roof
Section 17.2
Roof Framing with Common Rafters
Section 17.3
Ceiling Framing
Section 17.4
Roof Trusses
Chapter Objectives
After completing this chapter,
you will be able to:
• Identify the basic roof
styles.
• Understand the basic
terms relating to roof-
framing carpentry.
• Explain the layout of a
common rafter, using
at least one of the four
basic methods.
• Describe the layout
ceiling joists.
• Name the three basic
parts of a roof truss.
• Demonstrate how to
install roof trusses. Discuss the Photo
Building a Roof Roofs are constructed in many different shapes. What
are some things to consider in determining the shape of a roof?
Writing Activity: Research and Summarize
Contact a manufacturer of residential wood trusses. Find answers to
the following questions. Then summarize your fi ndings in a one-page report.
1. How long does it take to design a truss, and how far in advance should
a builder order them?
2. How are computers used in the design of trusses?
464 Chapter 17 Basic Roof Framing
Peter Salartos/Getty Images
17
Before You Read Preview
Roof framing is the last major framing activity in the construction of a house. Choose a
content vocabulary and academic vocabulary word that is new to you. When you fi nd it in
the text, write down the defi nition.
Content Vocabulary
●● rafter ●● unit run ●● pitch
●● ridge board ●● total rise ●● chord
●● span ●● unit rise ●● web
●● total run ●● slope
Academic Vocabulary
You will fi nd these words in your reading and on your tests. Use the academic vocabulary
glossary to look up their defi nitions if necessary.
■ benefi t ■ distributed ■ access ■ specify
Graphic Organizer
As you read, use a two-column chart like the one shown to organize content vocabulary
words and their defi nitions.
Content Vocabulary Defi nition
rafter A rafter is an inclined framing member that
supports the roof.
Go to glencoe.com for this book’s OLC for a downloadable version of this graphic organizer.
Academic Standards
Mathematics English Language Arts
Measurement: Apply appropriate techniques, tools, and Use different writing process elements to communicate
formulas to determine measurements (NCTM) effectively (NCTE 5)
Geometry: Use visualization, spatial reasoning, and Science
geometric modeling to solve problems (NCTM)
Algebra: Understand patterns, relations, and functions Science and Technology: Abilities of technological
(NCTM) design (NSES)
Geometry: Apply transformations and use symmetry to Science in Personal and Social Perspectives: Personal
analyze mathematical situations (NCTM) and community health (NSES)
Geometry: Analyze characteristics of two- and three- Life Science: Behavior of organisms (NSES)
dimensional geometric shapes and develop mathe- Industry Standards
matical arguments about geometric relationships (NCTM) Framing in Wood
Roof, Ceiling, and Wall Framing
NCTE National Council of Teachers of English NSES National Science Education Standards
NCTM National Council of Teachers of Mathematics
Chapter 17 Reading Guide 465
17.1 Planning a Roof
Roof Styles “Engineered Wood”). This and following
Which roof styles are most common chapters describe roof framing using con-
where you live? ventional lumber. Using I-joists requires the
same basic understanding of rafter layout
Roof framing is considered the most and roof design. Truss roof framing is cov-
complicated frame carpentry in a house ered in Section 17.4.
because of all the angles involved. It may The main purpose of a roof is to protect the
also seem diffi cult to learn because of the house in all types of weather with a minimum
many special terms. However, it is important of maintenance. The roof must be appropriate
to understand that even the most complex for the climate in which the house is being
roofs are based on a few standard designs. built. A roof must be strong to withstand
Roof framing begins after the house walls snow and wind loads. A roof should provide
have been framed. In most cases, the walls a continuous downward slope to shed rain
have also been sheathed to increase their water and snow melt. The parts must be
strength and stiffness. Nominal 2" lumber is securely fastened to each other to prevent
generally used for roof framing but I-joists them from coming apart in high winds or
are increasingly common (see Chapter 13, collapsing under a heavy load of snow.
Gable roof Gable roof & dormer Gable & valley roof
Gable roof with shed roof addition
Hip roof Hip & valley roof Low-slope (flat) roof
Shed or lean-to roof Gambrel roof Mansard roof Dutch hip roof
Figure 17-1 Common Roof Styles
Shape Determines Style Each style of roof has advantages and disadvantages.
466 Chapter 17 Basic Roof Framing
Geometry
Calculating Rafter Length Lawford
Construction is building a house with a
gabled roof that has a 24' span. The total
rise of the roof is 9'. How long should the
rafters be if the design calls for a 10" tail?
Starting Hint Use the Pythagorean
Theorem to fi gure the length of the rafter
from the ridge board to the top plate. Then
add the length of the rafter tail.
reduced. The hip is also a very strong roof
Figure 17-2 Two Styles of Roof and is often found in regions where severe
Multiple Styles Gable roofs and hip roofs are common storms are common.
styles in homebuilding. Which roof styles do you see on Low-Slope Roof
this house? Sometimes called a fl at roof, a low-slope roof
A carpenter must understand and be able to is not perfectly fl at. Instead, the rafters are
frame roofs in different styles. The basic roof laid at a slight angle to encourage water to
styles used for homes and small buildings drain. A rafter is an inclined framing mem-
are gable, hip, low-slope, and shed, as shown ber that supports the roof. Sheathing and
in Figure 17-1. Variations are associated with roofi ng are applied to the top of the rafters.
architectural styles of different regions or The ceiling material is applied to the under-
countries. Some of these include the gambrel side of the rafters. Because a fl at roof can be
roof, the mansard roof, and the Dutch hip roof. diffi cult to waterproof, it is found most often
A roof should also add to the attractiveness in dry climates.
of the home. Roof styles are used to create Shed Roof
different effects. A house may have more than Sometimes called a lean-to roof, the shed roof
one style of roof, as shown in Figure 17-2. slopes in one direction only. A shed roof is
Gable Roof often used for an addition to an existing struc-
The gable roof has two sloping sides that ture. In this case, the roof may be attached to
meet at the top to form a gable at each end. the side of the structure or to the roof.
A gable is the triangular wall enclosed by Gambrel Roof
the sloping ends of the roof. A gable roof The gambrel roof is a variation of the gable
may include dormers (upright window roof. It has a steep slope on two sides. A
projections) that add light and ventilation second slope begins partway up and contin-
to second-fl oor rooms or the attic. The gable ues to the top. It is commonly used on barns.
roof is the most common type of roof. A gambrel roof allows for more useable attic
Hip Roof space than a typical gable or hip roof. This
A hip roof slopes at the ends of the build- space can also be used as a second fl oor.
ing as well as at the two sides. The slope Mansard Roof
on all sides results in an even overhang The mansard roof is a variation of the hip
all around the building and gives a low roof. It has steep slopes on all four sides.
appearance. Because there is no siding Partway up, a shallow second slope is devel-
above the overhang, maintenance needs are oped and continues to the top where it meets
Section 17.1 Planning a Roof 467
Arnold & Brown
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