Roof framing is the most complex aspect of wood frame house construction and the most difficult to master. Getting the geometry of a roof frame to fit together, especially if it involves intricate roof elements like turrets or crickets, requires the skills of an experienced framing contractor. But the design process will need lots of input from the homeowner.
A key decision must be made regarding the roof style – gabled, hip, and gambrel are some common types. Secondary considerations such as roof pitch, overall building height, overhang, and dormers are influenced by aesthetic preferences and code restrictions, and are often interdependent.
Say for example, it is preferable to have an eight-inch pitch on the main gable. But due to height limitations, the pitch must be decreased to lower the elevation of the ridge or “peak.” Doing so will alter the width of the overhang and/or the distance of the eave (soffit and fascia) above ground level. This can result in an unsightly three-foot overhang or fascia boards that don’t align with other sections of the roof. If you plan to construct a large, complicated roof, it is advisable to retain the services of a licensed architect to work out such details. Here are the primary steps in the planning and construction of a roof frame.
Step 1 - Aesthetic Appearance and Practical Considerations
What is the roof pitch? What is the width of the overhang? Is an overhang along the gable end (a rake) desirable? Adding dormers to the roof will create additional head room or living space in the attic and will also provide natural daylighting. What style dormers would be appropriate – gable, hip, shed, and how much would dormers add to the cost of construction?
Step 2 - The Structural Design
The actual construction of the roof frame should be undertaken by licensed professionals (general contractor, engineer, architect). The selection of the dimensions and material, which determine the bearing capacity of the various framing members is based on pre-calculated data listed in tables from structural design manuals.
Step 3 - Purchase the Materials
Once the design has been finalized, you can proceed to tabulate the quantity, the dimensions and the lengths of the framing members by consulting the framing plans in the construction documents. This will provide you with a cost estimate and will enable you to place an order at the local lumber yard. You will need asphalt roof shingles and felt roofing paper to cover the surface area of the roof. Roofing shingles come in units called squares which cover an area of 100 square feet. You will also need to purchase material for the fascia, soffit, and trim.
Step 4 - Layout and Cut the Rafters
When the lumber arrives at the jobsite, the rafter material is gathered and a single pattern rafter is laid out from which all other rafters will be traced and cut. Accuracy is critical; a minute error in the pattern can result in a three foot difference in building height.
Step 5 - Assemble the Frame
Lean the cut rafters along the wall’s top plate so they will be easily accessible. Install the ridge board and attach the rafters one at a time; nail first at the ridge and then at the plate. Install any secondary members – gable ends, hips, valleys and jack rafters. Install collar ties, purlin and bracing as needed for the rafters and ridge to prevent sagging. The last stage of the roof framing is the installation of lookout blocks at each rafter tail along the overhang for the soffit.
Step 6 - Finish the Roof
Finally, apply the drip edge, roofing paper, roof shingles, fascia, soffit and trim.