Structure Inspection Section#4 Roof Framing Quiz#2

You should have finished Study Session 1 and Quick Quiz 1 before starting this Study Session. This section introduces our discussion of rafters and roof and ceiling joists.

The estimated completion time is 45 minutes.

Objectives
At the end of this Study Session, you should be able to:

• List five functions of rafters, roof joists, and ceiling joists.
• Define in one sentence each rafters, roof joists and ceiling joists.
• Describe in one sentence each hip, valley and jack rafters, and ridge boards and ridge beams.

Ceiling joists are often not continuous from one side of the building to the other. In this case, they are spliced over a central bearing wall. Why do they have to be securely tied together?

Ceiling joists help prevent rafters and the tops of walls from being pushed outward by live loads on the roof. Ceiling joists are often in tension, running from the bottom of one rafter to another. They must be continuous to resist these forces.

Define hip rafter, valley rafter, and jack rafter.

A hip rafter is a rafter that forms a roof hip and supports the jack rafters on either side. The hip rafter follows the line of the hip. A valley rafter follows the line of the valley in a roof and supports the jack rafters on either side. Hip and valley rafters are typically one size larger than other rafters in the roof structure. Jack rafters are short rafters that either have their top end at a hip rafter or their bottom end at a valley rafter.

Define rafters, roof joists, and ceiling joists

Rafters are sloped structural members on steep roofs that support sheathing and run from the roof peak down to the eaves. They may be 2 by 4 to 2 by 10?s and are typically spaced 12 ? 24 inches on center. Roof joists are horizontal or nearly horizontal framing members on low-sloped roofs that carry the sheathing, roof covering and live loads above to walls or beams. Roof joists can be thought of as low-sloped rafters. Some roof joists also carry ceiling finishes. Ceiling joists are horizontal members that support insulation and ceilings. They are used with rafters and may support attic floors. Ceiling joists often tie the bottom ends of opposing rafters together to make a structurally sound triangle of the roof assembly.

How is the span of a rafter measured?

The span of a rafter is determined by its horizontal projection.

List five functions of roof framing members.

1. Carry the live loads of wind, rain, snow and people

2. Carry the dead loads of roof sheathing, roof covering and roof-mounted equipment

3. Support the dead loads of insulation and ceiling finishes

4. Laterally support the walls of the building, preventing racking and wall or roof spreading

5. Create an attic space, a ventilation space and support for soffit and fascia

What is a typical, chronic problem with flat and cathedral roofs?

One of the chronic problem with both flat and cathedral roofs is a lack of ventilation. Where insulation is between the roof joists or rafters, there should be a space above to allow moist air and heat to be removed from the roof space. 

What is the difference between a ridge board and a ridge beam?

A ridge board does not carry rafter loads. A ridge beam does. A ridge beam will prevent rafter spreading. A ridge board will not. A ridge board is typically 1 by x material. A ridge beam is typically at least 2 by x material. Ridge beams require vertical supports below. Ridge boards do not.