One of the strongest ways to frame a roof is using a hip-roof design. The planes of the roof slope up from every side, so the framing braces the roof from all sides. If the building is square and the sides are of equal length, the roof planes will meet at a point, as in a pyramid. On a rectangular-shaped building with a hip roof, the roof planes on the two longer sides meet at a ridge, as shown in the illustration below.
The key structural member is the hip rafter, which spans from the building corner to the peak or the ridge. Before we explain hip rafters, you need to understand how to lay out and cut common roof rafters; this is covered in “Cutting Common Rafters” (Mar/17). There are many variations on hip roofs and their construction, but for the purpose of this article, let’s assume that the roof planes are all the same slope (6:12) and that they meet at a ridge. For simplicity, we will make all of the framing out of 2-by stock.
Spoiler alert
If you were to show the method I describe here to many seasoned framers, they would dismiss it as the work of a weekend warrior or a newbie. But given that this column is for tradespeople just starting out or those who may not frame roofs on a regular basis, I wanted to present a simple foolproof approach that anyone can follow for laying out a hip roof. This method is a great fallback that eliminates having to go through the mathematical machinations that the traditional methods for laying out a hip rafter typically require. For an excellent article on the traditional way to frame a hip roof, take a look at Tim Uhler’s Framing a Hip Roof, Sep/13.
Objective:
To understand how a hip rafter functions in a hip roof and to understand this particular method of calculating and cutting the hip rafter
Prerequisite skills:
- An understanding of basic roof framing and rafter cutting.
- Familiarity and basic skills with a circular saw.
- Ability to take accurate measurements and record them.
- Familiarity and basic skills with a framing square.
Tools:
- Measuring tape
- Framing square
- Stair gauges
- Circular saw
Vocabulary:
- Common rafters: Roof framing members that go from the top wall plates to the ridge.
- King common rafters: Common rafters in a hip roof that meet at right angles on either side of the hip rafter.
- Height above plate: Distance on a rafter measured in a plumb line from the top outside edge of the plate to the top edge of the rafter.
- Hip rafter length (or line length): The length of a hip rafter based on calculations from a framing square or a construction calculator.
- Plumb cut: A cut on a rafter or other angled framing member that will be plumb vertically when the member is installed.
- Seat cut: A cut on a rafter or other angled framing member that will be level when the member is installed.
- Bevel cut: A cut made with the saw blade set an angle.
- Birdsmouth: The triangular cut at the bottom of a rafter where it sits on the plates.
