Hip, Valley, & 18 Jack Rafters - Mr. Wilsons Technology Site

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Section 18.1 Hip Rafters

Section 18.2 Valley Rafters

Section 18.3 Jack Rafters

Hip, Valley, & Jack Rafters

Chapter Objectives

After completing this chapter, you will be able to:

? Explain how to lay out a hip rafter for a given roof.

? Explain how to lay out a valley rafter for a given roof.

? Determine the rafter overhang for a hip or valley rafter.

? Define a dormer. ? Explain how to lay out

a jack rafter for a given roof.

? Summarize why the intersection of two roofs calls for more complex framing.

Discuss the Photo

Rafters Rafters are made up of geometric shapes. What shapes and types of angles do you see in this picture?

Writing Activity: Categorizing Information As a class, observe or find photographs of at least sixteen different roofs on houses in your community. Place like roofs together. After you have finished reading the chapter, categorize each roof by type: gable roofs, hip roofs, and intersecting roofs (including dormers). Create a brief description of each type of roof.

502 Chapter 18 Hip, Valley, & Jack Rafters

Photodisc/Getty Im ages

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Before You Read Preview

Roof framing with hip, valley, and jack rafters is more complex than framing entirely with common rafters. Choose a content vocabulary or academic vocabulary word that is new to you. When you find it in the text, write down the definition.

Content Vocabulary

hip rafter valley rafter jack rafter

seat cut backing the hip dropping the hip

addition dormer doghouse dormer

Academic Vocabulary

You will find these words in your reading and on your tests. Use the academic vocabulary glossary to look up their definitions if necessary.

hypotenuse

significant

ensure

Graphic Organizer

As you read, use a chart like the one shown to organize information about the three types of rafters.

hip rafter

forms a raised area, or hip, usually extending from the corner of the building diagonally upwards to the ridge

valley rafter

jack rafter

Go to for this book's OLC for a downloadable version of this graphic organizer.

Academic Standards

English Language Arts

Use information resources to gather information and create and communicate knowledge (NCTE 8) Participate as members of literacy communities (NCTE 11)

Mathematics

Measurement: Understand measurable attributes of objects and the units, systems, and processes of measurements (NCTM) Geometry: Analyze characteristics and properties of two- and three-dimensional geometric shapes and develop mathematical arguments about geometric relationships (NCTM)

NCTE National Council of Teachers of English NCTM National Council of Teachers of Mathematics

Science Science and Technology: Abilities of technological design (NSES) Industry Standards Framing in Wood Roof, Ceiling, and Wall Framing

NSES National Science Education Standards

Chapter 18 Reading Guide 503

Hip Rafters

18.1

Understanding Complex

Roofs

When is a hip rafter called for?

A simple gable roof can be built entirely with common rafters. However, a carpenter must also know how to lay out and cut hip, valley, and jack rafters. These rafters, shown in Figure 18-1, are required when framing complex roofs, such as hip roofs and intersecting gable roofs (for more on roof types, see Chapter 17, "Basic Roof Framing"). A hip rafter forms a raised area, or hip, usually extending from the corner of the building diagonally upwards to the ridge. A valley rafter forms a depression in the roof instead of a hip. Like the hip rafter, it extends diagonally from the top plate to the ridge. A hip

rafter is called for only when framing a hip roof, but a valley rafter is needed on both hip and gable roofs whenever roof planes intersect. A jack rafter is a shortened common rafter that may be framed to a hip rafter, a valley rafter, or both. Thus, there are hip jack rafters and valley jack rafters.

The total rise of hip and valley rafters is the same as that of common rafters. They are also the same thickness as common rafters. However, they should be 2" wider in their nominal dimension. For example, if you use 26 common rafters, use 28 hip rafters to provide full bearing for the end of intersecting jack rafters, as shown in Figure 18-2.

A mastery of roof framing with hip, valley, and jack rafters is what distinguishes the true

Hip rafter

Main roof valley jacks

Ridge board

Addition valley jacks

Ridge board Common rafter

Ridge

Hip jacks

Valley rafter

A

B

Figure 18-1 Hip, Jack, and Valley Rafters Roof Anatomy A. The roof framing plan. B. The general arrangement of rafters shown in the larger drawing.

504 Chapter 18 Hip, Valley, & Jack Rafters

Doubled valley rafters

Valley jack rafter

Common rafter

Common rafter with overhang

Top plate

Figure 18-2 Width of Hip and Valley Rafters How the Parts Fit The doubled valley rafter in this drawing has been cut off at the top plate. Normally it is extended to become part of the overhang. Doubled valleys are sometimes used to provide more bearing for the roof sheathing.

professional from the casual carpenter. This chapter describes how to figure rafter layouts manually using a standard framing square. On the job, construction calculators and triangular framing squares are often used for this purpose. A calculator works quickly and with great precision. This makes it invaluable when laying out hip, valley, and jack rafters. Most construction calculators have built-in functions to make roof calculations even easier.

total run of the rafter, but not its actual length. On a hip roof framing plan, the lines that indicate the hip rafters (EC, AC, KG, and IG in Figure 18-3) form 45? angles with the edges of the building. You can see from the plan that the total run of a hip rafter is the hypotenuse of a right triangle. The two shorter legs of this triangle are each equal to the total run of a common rafter, or half the span of the roof.

Length of building

E

D

H

I

Recall What tools are used to figure layouts?

Hip Rafter Layout

What is a hypotenuse?

Any of the methods for determining the length of a common rafter may be used for determining the length of a hip rafter (see Chapter 17, "Basic Roof Framing"). However, some of the basic data used is different.

Part of a framing plan for a hip roof is shown in Figure 18-3. Remember that a line on the framing plan indicating a rafter represents the

F

C

G

A

B

L Run K

Figure 18-3 Hip Roof Framing Plan Framing Plan This is the framing plan for a small rectangular building with a hip roof.

Span of building Run

Section 18.1 Hip Rafters 505

In Figure 18-4, one corner of the roof framing plan (ABCF in Figure 18-3) has been drawn in perspective. This shows the relative position of the hip rafter to the common rafter.

The unit run of a hip rafter is the hypotenuse of a right triangle with the shorter sides each equal to the unit run of a common rafter, as shown in Figure 18-5. The unit run of a common rafter is 12". Using the Pythagorean theorem, a2 b2 c2, the unit run of a hip rafter is the square root of 144 144 which is 16.97" (which can be rounded up to 17"), as shown in Figure 18-6A.

Like the unit length of a common rafter, the unit length of a hip rafter may be obtained from the rafter table on the framing square. In Figure 18-6B, the second row in the table is headed "Length Hip or Valley per Foot Run." This means "for every 12" of a common rafter in the same roof." Another way to state this would be "per 16.97" run of hip or valley rafter." For example, the unit length for a unit rise of 8" is 18.76". To calculate the length of a hip rafter, multiply the unit length by the number of feet in the total run of a common rafter.

Cutting Compound Angles The cuts made on hip jack and valley jack rafters are typically made at compound angles. To make such cuts, tilt a portable saw at a bevel angle. Then guide it across the rafter stock at a miter angle. Secure the stock so it will not move during the cut. To prevent the blade guard from binding, retract it to get the cut started. Then release it to complete the cut. Never disable or remove the guard to make a compound-angle cut.

Go to for this book's OLC for more on job safety.

Look again at Figure 18-5, which shows the corner of the building shown in Figure 18-3. In this example the total run of a common rafter is 5'. The unit rise is 8" and the unit length of the hip rafter for this unit rise is 18.76". The unit length multiplied by the total run in feet is the length of the hip rafter in inches (18.76" 5 93.8", or 7'-913/16"). As in the case of common rafters, this is the theoretical length. To obtain the actual length, the ridge board shortening allowance and the rafter tail length will have to be calculated and laid out.

Square prism

Common rafter Rise

of roof 3'? 4"

Corner of building

A

Figure 18-4 Comparison of Hip and Common Rafters Hip and Common Rafters Here, the position of a hip rafter is shown relative to a common rafter. Which one is longer?

C' F Hip rafter

Run of hip rafter

C

Portion 5'? 0"

of

plate

9 0? B

Run of com5'?m0o"n rafter

506 Chapter 18 Hip, Valley, & Jack Rafters

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