Jack Rafter

Definition

A jack rafter is a shortened rafter that connects a hip or valley rafter to the top of the wall plate.

Purpose

The jack rafter plays a critical role in the construction of roofs, particularly in areas where hips or valleys are present. It ensures structural integrity and aids in distributing the load evenly from the roof to the walls. By connecting hip or valley rafters to the wall plate, jack rafters help create the desired roof shape and support the roof covering.

Examples of Use

1. Hip Roof Construction: In a hip roof, jack rafters are used to fill the spaces between the common rafters and the hip rafter, providing a smooth transition and supporting the roofing material.
2. Valley Roof Construction: For valley roofs, jack rafters connect to the valley rafter, allowing for proper drainage and structural support where two roof planes meet.
3. Dormer Construction: Jack rafters can also be found in dormer structures, where they connect the main roof to the dormer roof, ensuring a seamless integration.

Related Terms

• Hip Rafter: A diagonal rafter that forms the intersection of two roof slopes.
• Valley Rafter: A rafter that forms the internal angle where two roof slopes meet.
• Common Rafter: A rafter that extends from the wall plate to the ridge board.
• Wall Plate: A horizontal timber member that sits on top of a wall and supports the rafters.

Notes

When installing jack rafters, it's important to ensure they are properly aligned and securely fastened to both the hip or valley rafter and the wall plate. This alignment is crucial for maintaining the structural integrity and aesthetics of the roof.