How to Design Eaves for Your Home
This article will provide some useful information to help you in designing eaves for your home. Specifically, it will explain the proper technique for designing and constructing the overhang created by the extension of the rafter “tails” beyond the exterior wall, otherwise known as the eave. The method discussed in this article relates to conventional wood frame construction. If you’re able to do basic carpentry, you’ll find that designing and building the eave is a simple and straightforward procedure.
Step 1 - What is an Eave?
The modern eaves that are found on traditional residential structures have evolved over time to provide multiple functions. Overhangs can extend horizontally anywhere from a few inches to greater than 2 feet. The larger overhangs can provide overhead cover from precipitation as well as sun shading. The eaves extend outward beyond the wall to ensure the ice, snow and water that is shed from the roof falls clear of the exterior wall.
Step 2 - Eave Design Basics
The style or form that the eave takes is a matter of preference, but is directly related and inversely proportional to the pitch or slope of the roof. A shallow roof pitch will result in a larger overhang, but one that has a higher elevation above the grade (ground) level. A steep pitch will result in a smaller overhang, but one that is closer to the ground. Stated in another way - if you wish to maintain the horizontal distance of the overhang, decreasing the roof pitch will increase the eave elevation (above ground level), and increasing the roof pitch will decrease the eave elevation. Furthermore, if the objective is to keep the eave at a specific height above ground level, decreasing the roof pitch will increase the horizontal overhang and vice versa.
Step 3 - Other Considerations
It is important to understand how the three design components – horizontal overhang distance, vertical height above grade level, and roof pitch – are inter-related. This will become obvious when designing other exterior wall elements. For example, if a window is to maintain a particular height above floor level, the eave cannot extent down below the designated window height. Another consideration is that it is often desirable to align the height of the fascia and trim that is installed onto the eave with adjacent roof sections.
Step 4 - Design the Eave
The eave itself is designed by laying out and cutting a rafter pattern. All that is needed for this is the roof pitch and the horizontal overhang. Using a framing square set at the desired pitch, trace the plumb cut and level cut for the rafter tail. Measure the horizontal overhang distance and trace the plumb cut and level cut for the bird’s mouth. Step off the run of the rafter in one foot horizontal increments and scribe the plumb cut for the ridge board. Using this original as a pattern, trace and cut the remaining rafters. When the roof is assembled, your eave will look just as you envisioned it.